Internet Draft                             Electronic Signature Formats
Internet Draft                                       ETSI TC-SEC (ETSI)
S/MIME Working Group                                   D. Pinkas (Bull)
expires in six months                    J. Ross (Security & Standards)
Target Category: Informational           N. Pope (Security & Standards)
                                                              July
                                                          November 2000

                     Electronic Signature Formats
                  for long term electronic signatures
                  <draft-ietf-smime-esformats-02.txt>
                  <draft-ietf-smime-esformats-03.txt>

Status of this Memo

   This document is an Internet-Draft and is NOT offered in
   accordance with section of RFC 2026, and the author does not
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Abstract

The informational RFC defines the format of an electronic signature
that can remain valid over long periods. This includes evidence as to
its validity even if the signer or verifying party later attempts to
deny (i.e. repudiates, see [ISONR]) the validity of the signature.

The format can be considered as an extension to RFC 2630 [CMS] and RFC
2634 [ESS], where, when appropriate additional signed and unsigned
attributes have been defined.

The contents of this Informational RFC is technically equivalent to
ETSI ES 201 TS 101 733 V.1.1.3 V.1.2.2 Copyright (C). Individual copies of this
ETSI deliverable can be downloaded from http://www.etsi.org

1.  Introduction

This document is intended to cover electronic signatures for various
types of transactions, including business transactions (e.g. purchase
requisition, contract, and invoice applications) where long term
validity of such signatures is important.

Internet Draft                             Electronic Signature Formats

Electronic signatures can be used for any transaction between an
individual and a company, between two companies, between an individual
and a governmental body, etc. This document is independent of any
environment. It can be applied to any environment e.g. smart cards, GSM
SIM cards, special programs for electronic signatures etc.

An electronic signature produced in accordance with this document
provides evidence that can be processed to get confidence that some
commitment has been explicitly endorsed under a signature policy, at a
given time, by a signer under an identifier, e.g. a name or a
pseudonym, and optionally a role.

The European Directive on a community framework for Electronic
Signatures defines an electronic signature as: "data in electronic form
which is attached to or logically associated with other electronic data
and which serves as a method of authentication".  An electronic
signature as used in the current document is a form of advanced
electronic signature as defined in the Directive.

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase,
as shown) are to be interpreted as described in [RFC2119].

TABLE OF CONTENTS

1.  Introduction                                                    1
2  Overview                                                         4
2.1  Aim                                                            4
2.2  Basis of Present Document                                      4
2.3  Major Parties                                                  5
2.4  Electronic Signatures and Validation Data                      6
2.5  Forms of Validation Data                                       7
2.6  Extended Forms of Validation Data                              9                             10
2.7  Archive Validation Data                                       11                                       12
2.8  Arbitration                                                   12                                                   13
2.9  Validation Process                                            12                                            13
2.10  Example Validation Sequence                                  13                                  14
2.11  Additional optional features                                 18                                 19
3. Data structure of an Electronic Signature                       19                       20
3.1  General Syntax                                                19                                                20
3.2  Data Content Type                                             19                                             20
3.3  Signed-data Content Type                                      19                                      20
3.4  SignedData Type                                               19                                               20
3.5  EncapsulatedContentInfo Type                                  20                                  21
3.6  SignerInfo Type                                               20                                               21
3.6.1  Message Digest Calculation Process                          20                          21
3.6.2  Message Signature Generation Process                        20                        21
3.6.3  Message Signature Verification Process                      20                      21
3.7  CMS Imported Mandatory Present Attributes                     21                     22
3.7.1  Content Type                                                21                                                22
3.7.2  Message Digest                                              21                                              22
3.7.3  Signing Time                                                21                                                22

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3.8  Alternative Signing Certificate Attributes                    21                    22
3.8.1  ESS Signing Certificate Attribute Definition                21                22
3.8.2  Other Signing Certificate Attribute Definition              22              23
3.9  Additional Mandatory Attributes                               23                               24
3.9.1  Signature policy Identifier                                 23                                 24
3.10  CMS Imported Optional Attributes                             24                             26
3.10.1  Countersignature                                           25                                           26
3.11  ESS Imported Optional Attributes                             25                             26
3.11.1  Content Reference Attribute                                 25                                27
3.11.2  Content Identifier Attribute                               25                               27
3.11.3  Content Hints Attribute                                    27
3.12   Additional Optional Attributes                              25                              28
3.12.1  Commitment Type Indication Attribute                       25                       28
3.12.2  Signer Location attribute                                  27                                  30
3.12.3  Signer Attributes attribute                                28                                31
3.12.4  Content Timestamp attribute                                28                                31
3.13  Support for Multiple Signatures                              29                              32
3.13.1  Independent Signatures                                     29                                     32
3.13.2  Embedded Signatures                                        29                                        32
4.  Validation Data                                                29                                                32
4.1  Electronic Signature Timestamp                                30                                33
4.1.1  Signature Timestamp Attribute Definition                    30                    33
4.2  Complete Validation Data                                      31                                      34
4.2.1  Complete Certificate Refs Attribute Definition              32              35
4.2.2  Complete Revocation Refs Attribute Definition               32               35
4.3  Extended Validation Data                                      34                                      37
4.3.1  Certificate Values Attribute Definition                     34                     37
4.3.2  Revocation Values Attribute Definition                      35                      38
4.3.3  ES-C Timestamp Attribute Definition                         35                         38
4.3.4  Time-Stamped Certificates and CRLs Attribute Definition     36     39
4.4  Archive Validation Data                                       36                                       39
4.4.1  Archive Timestamp Attribute Definition                      37                      40
5.  Security considerations                                        38                                        41
5.1  Protection of Private Key                                     38                                     41
5.2  Choice of Algorithms                                          38                                          41
6.  Conformance Requirements                                       38                                       41
6.1  Signer                                                        38                                                        41
6.2  Verifier                                                      39 using timestamping                                   42
6.3  Verifier using secure records                                 42
7. References                                                      40                                                      43
8. Authors' Addresses                                              40                                              44
9. Full Copyright Statement                                        41                                        45
Annex A (normative): ASN.1 Definitions                             43                             46
A.1  Definitions Using X.208 (1988) ASN.1 Syntax                   43                   46
A.2  Definitions Using X.680 1997 ASN.1 Syntax                     52                     54
Annex B (informative): General Description                         61                         64
B.1  The Signature Policy                                          61                                          64
B.2  Signed Information                                            62                                            65
B.3  Components of an Electronic Signature                         62                         65
B.3.1  Reference to the Signature Policy                           62                           65
B.3.2  Commitment Type Indication                                  63                                  66
B.3.3  Certificate Identifier from the Signer                      64                      67

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B.3.4.  Role Attributes                                            64                                            68
B.3.4.1  Claimed Role                                              65                                              68
B.3.4.2  Certified Role                                            65                                            68
B.3.5  Signer Location                                             66                                             69
B.3.6  Signing Time                                                66                                                69
B.3.7  Content Format                                              70
B.4  Components of Validation Data                                 67                                 70
B.4.1  Revocation Status Information                               67                               70
B.4.2  CRL Information                                             67                                             71
B.4.3  OCSP Information                                            68                                            72
B.4.4  Certification Path                                          69                                          72
B.4.5  Timestamping for Long Life of Signature                     69                     73
B.4.6  Timestamping before CA Key Compromises                      70                      74
B.4.6.1  Timestamping the ES with Complete validation data         71         75
B.4.6.2  Timestamping Certificates and Revocation Information      72      75
B.4.7  Timestamping for Long Life of Signature                     72                     76
B.4.8  Reference to Additional Data                                73                                77
B.4.9  Timestamping for Mutual Recognition                         73                         77
B.4.10  TSA Key Compromise                                         74                                         78
B.5  Multiple Signatures                                           74                                           79
Annex C (informative):  Identifiers and roles                      75                      79
C.1  Signer Name Forms                                             75                                             79
C.2  TSP Name Forms                                                75                                                79
C.3  Roles and Signer Attributes                                   75                                   80

2  Overview

2.1  Aim

The aim of this document is to define an Electronic Signature (ES) that
remains valid over long periods. This includes evidence as to its
validity even if the signer or verifying party later attempts to deny
(repudiates) the validity of the signature.

This document specifies the use of trusted service providers (e.g.
TimeStamping Authorities (TSA)), and the data that needs to be archived
(e.g. cross certificates and revocation lists) to meet the requirements
of long term electronic signatures. An electronic signature defined by
this document can be used for arbitration in case of a dispute between
the signer and verifier, which may occur at some later time, even years
later. This document uses a signature policy, referenced by the signer,
as the basis for establishing the validity of an electronic signature.

2.2  Basis of Present Document

This document is based on the use of public key cryptography to produce
digital signatures, supported by public key certificates.

A Public key certificate is a public keys of a user, together with some
other information, rendered unforgeable by encipherment with the
private key of the Certification Authority (CA) which issued it (ITU-T
Recommendation X.509 [1]).

Internet Draft                             Electronic Signature Formats

This document also specifies the uses of timestamping services to prove
the validity of a signature long after the normal lifetime of critical
elements of an electronic signature and to support non-repudiation. It
also, as an option, uses defines the use of additional timestamps to provide
very long-term protection against key compromise or weakened
algorithms.

This document builds on existing standards that are widely adopted.
This includes:

     * RFC 2459 [RFC2459] Internet X.509 Public Key Infrastructure
       Certificate and CRL Profile (PKIX);
     * RFC 2630 [CMS] Crytographic Message Syntax (CMS);
     * RFC 2634 [ESS] Enhanced Security Services (ESS);
     * RFC 2439 [OCSP] One-line Certificate Status Protocol (OCSP);
     * ITU-T Recommendation X.509 [1] Authentication framework;
     * RFC (to be published) [TSP] PKIX Time Stamping protocol (TSP).

NOTE:  See clause 8 for a full set of references.

2.3  Major Parties

The following are the major parties involved in a business transaction
supported by electronic signatures as defined in this document:

     * the Signer;
     * the Verifier;
     * the Arbitrator;
     * Trusted Service Providers (TSP).

A Signer is an entity that initially creates the electronic signature.
When the signer digitally signs over data using the prescribed format,
this represents a commitment on behalf of the signing entity to the
data being signed.

A verifier is an entity that verifies an evidence. (ISO/IEC 13888-1
[13]). Within the context of this document this is an entity that
validates an electronic signature.
An arbitrator, is an entity which arbitrates disputes between a signer
and a verifier when there is a disagreement on the validity of a
digital signature.

Trusted Service Providers (TSPs) are one or more entities that help
to build trust relationships between the signer and verifier. Use of
some specific TSP services MAY be mandated by signature policy. TSP
supporting services may provide the following information: user
certificates, cross-certificates, timestamping tokens, CRLs, ARLs,
OCSP responses.

Internet Draft                             Electronic Signature Formats

The following TSPs are used to support the validation or
the verification of electronic signatures :

     * Certification Authorities;
     * Registration Authorities;
     * Repository Authorities (e.g. a Directory);
     * TimeStamping Authorities;
     * One-line Certificate Status Protocol responders;
     * Attribute Authorities;
     * Signature Policy Issuers.

Certification Authorities provide users with public key certificates.

Registration Authorities allows the registration of entities before a
CA generates certificates.

Repository Authorities publish CRLs issued by CAs, cross-certificates
(i.e. CA certificates) issued by CAs, signature policies issued by
Signature Policy Issuers and optionally public key certificates (i.e.
leaf certificates) issued by CAs.

TimeStamping Authorities attest that some data was formed before a
given trusted time.

One-line Certificate Status Protocol responders (OSCP responders)
provide information about the status (i.e. revoked, not revoked,
unknown) of a particular certificate.

A Signature Policy Issuer issues signatures policies that define the
technical and procedural requirements for electronic signature
creation, validation and verification, in order to meet a particular
business need.

Attributes Authorities provide users with attributes linked to public
key certificates

2.4  Electronic Signatures and Validation Data

Validation of an electronic signature in accordance with this document
requires:

     * The electronic signature; this includes:

        -  the signature policy;
        -  the signed user data;
        -  the digital signature;
        -  other signed attributes provided by the signer;
.       -  other unsigned attributes provided by the signer.

    * Validation data which is the additional data needed to validate
      the electronic signature; this includes:

        -  certificates references;
        -  certificates;

Internet Draft                             Electronic Signature Formats

        -  revocation status information references;
        -  revocation status information;
        -  time-stamps from Time Stamping Authorities (TSAs).

     * The signature policy specifies the technical requirements on
       signature creation and validation in order to meet a particular
       business need. A given legal/contractual context may recognize a
       particular signature policy as meeting its requirements.

For example: a specific signature policy may be recognized by court
of law as meeting the requirements of the European Directive for
electronic commerce. A signature policy may be written using a formal
notation like ASN.1 or in an informal free text form provided the
rules of the policy are clearly identified. However, for a given
signature policy there shall be one definitive form which has a unique
binary encoded value.

Signed user data is the user's data that is signed.

The Digital Signature is the digital signature applied over the
following attributes provided by the signer:

    * hash of the user data (message digest);
    * signature Policy Identifier;
    * other signed attributes

The other signed attributes include any additional information which
must be signed to conform to the signature policy or this document
(e.g. signing time).

The

According to the requirements of a specific signature policy in use,
various Validation Data may shall be collected and attached to or
associated with the signature structure by the signer and/or the verifier
and must meet the requirements of the signature policy.  Additional
verifier. The validation data includes CA certificates as well as
revocation status information in the form of Certificate Revocation Lists certificate revocation
lists (CRLs) or certificate status information provided by an on-line
service. Additional data also includes timestamps and other time
related data used to provide evidence of the timing of given events. It
is required, as a minimum, that either the signer or verifier obtains a
timestamp over the signer's signature.

A digital signature (not to be confused with an electronic signature)
is data appended to, or a cryptographic transformation of, a data unit
that allows a recipient secure time record of the data unit to prove the source
electronic signature must be maintained. Such secure records must not
be undetectably modified and
integrity of must record the data unit and protect against forgery, e.g. by time close to when the
recipient (ISO 7498-2 [12])
signature was first validated.

2.5  Forms of Validation Data

An electronic signature may exist in many forms including:

    * the Electronic Signature (ES), which includes the digital
      signature and other basic information provided by the signer;

Internet Draft                             Electronic Signature Formats

    * the ES with Timestamp (ES-T), which adds a timestamp to the
      Electronic Signature, to take initial steps towards providing
      long term validity;

    * the ES with Complete validation data (ES-C), which adds to the
      ES-T references to the complete set of data supporting the
      validity of the electronic signature (i.e. revocation status
      information).

The signer must provide at least the ES form, but in some cases may
decide to provide the ES-T form and in the extreme case could provide
the ES-C form. If the signer does not provide ES-T, the verifier must
either create the ES-T on first receipt of an electronic signature. The ES-T
provides signature or
shall keep a secure time record of the ES. Either of these two
approaches provide independent evidence of the existence of
the signature at the time it was first verified which should be near
the time it was created, and so protects against later repudiation of
the existence of the signature. If the signer does not provide ES-C the
verifier must create the ES-C when the complete set of revocation and
other validation data is available.

The ES satisfies the legal requirements for electronic signatures as
defined in the European Directive on electronic signatures, see Annex C
for further discussion on relationship of this document to the
Directive. It provides basic authentication and integrity protection
and can be created without accessing on-line (timestamping) services.
However, without the addition of a timestamp or a secure time record
the electronic signature does not protect against the threat that the
signer later denies having created the electronic signature (i.e. does
not provide non-repudiation of its existence).

The ES-T time-stamp or time record should be created close to the time
that ES was created to provide protection against repudiation. At this
time all the data needed to complete the validation may not be
available but what information is readily available may be used to
carry out some of the initial checks. For example, only part of the
revocation information may be available for verification at that point
in time. Generally, the ES-C form cannot be created at the same time as
the ES, as it is necessary to allow time for any revocation information
to be captured. Also, if a certificate is found to be temporarily
suspended, it will be necessary to wait until the end of the suspension
period.

The signer should only create the ES-C in situations where it was
prepared to wait for a sufficient length of time after creating the ES
form before dispatching the ES-C. This, however, has the advantage that
the verifier can be presented with the complete set of data supporting
the validity of the ES.

Support for ES-C by the verifier is mandated (see clause 6 for
specific conformance requirements).

Internet Draft                             Electronic Signature Formats

An Electronic Signature (ES), with the additional validation data
forming the ES-T and ES-C is illustrated in Figure 1:

+------------------------------------------------------------ES-C-----+
|+--------------------------------------------ES-T-----+              |
||+------Elect.Signature (ES)----------+ +------------+| +-----------+|
|||+---------+ +----------+ +---------+| |Timestamp   || |Complete   ||
||||Signature| |  Other   | | Digital || |over digital|| |certificate||
||||Policy ID| |  Signed  | |Signature|| |signature   || |and        ||
||||         | |Attributes| |         || +------------+| |revocation ||
|||+---------+ +----------+ +---------+|               | |references ||
||+------------------------------------+               | +-----------+|
|+-----------------------------------------------------+              |
+---------------------------------------------------------------------+

Figure 1: Illustration of an ES, ES-T and ES-C

2.6  Extended Forms of Validation Data

The complete validation data (ES-C) described above may be extended to
form verifiers conformance requirements of an ES with eXtended validation data (ES-X) to meet following
additional requirements.

Firstly, when the verifier does not has access to,

     * the signer's certificate,
     * all a timestamp of the CA certificates that make up
digital signature is defined in subclause 6.2.

The ES on its own satisfies the full certification
       path,
     * all legal requirements for electronic
signatures as defined in the associated revocation status information, European Directive on electronic
signatures. The signers conformance requirements of an ES are defined
in subclause 6.1, and are met using a structure as referenced indicated in figure
2:

+------Elect.Signature (ES)-----------|
|+---------+ +----------+ +---------+ |
||Signature| |  Other   | | Digital | |
||Policy ID| |  Signed  | |Signature| |
||         | |Attributes| |         | |
|+---------+ +----------+ +---------+ |
|+-----------------------------------+|

Figure 2: Illustration of an ES

Where there are requirements for long term signatures without
timestamping the ES-C. digital signature, then a secure record is needed of
the values time of these verification in association with the electronic signature
(i.e. both must be securely recorded).  In addition the certificates
and revocation information may be
added to the ES-C. This form of extended validation data is called a
X-Long.

Secondly, if there is a risk that any CA keys used in at the certificate
chain may time of verification should to
be compromised, then recorded as indicated in figure 3 as an ES-C(bis).

Internet Draft                             Electronic Signature Formats

+-------------------------------------------------------ES-C-----+
|                                                                |
| +------Elect.Signature (ES)----------+|           +-----------+|
| |+---------+ +----------+ +---------+||           |Complete   ||
| ||Signature| |  Other   | | Digital |||           |certificate||
| ||Policy ID| |  Signed  | |Signature|||           |and        ||
| ||         | |Attributes| |         |||           |revocation ||
| |+---------+ +----------+ +---------+||           |references ||
| +------------------------------------+|           +-----------+|
|                                                                |
+----------------------------------------------------------------+

Figure 3: Illustration of an ES-C(bis)

The verifiers conformance requirements of an ES-C(bis) is defined in
subclause 6.3.

Note: A timestamp attached to the electronic signature or a secure time
record helps to protect the validity of the signature even if some of
the verification data associated with the signature become compromised
AFTER the signature was generated. The timestamp or a secure time
record provides evidence that the signature was generated BEFORE the
event of compromise; hence the signature will maintain its validity
status.

2.6  Extended Forms of Validation Data

The complete validation data (ES-C) described above may be extended to
form an ES with eXtended validation data (ES-X) to meet following
additional requirements.

Firstly, when the verifier does not has access to,

     * the signer's certificate,
     * all the CA certificates that make up the full certification
       path,
     * all the associated revocation status information, as referenced
       in the ES-C.

then the values of these certificates and revocation information may be
added to the ES-C. This form of extended validation data is called a
X-Long.

Secondly, if there is a risk that any CA keys used in the certificate
chain may be compromised, then it is necessary to additionally
timestamp the validation data by either:

     * timestamping all the validation data as held with the ES(ES-C),
       this eXtended validation data is called a Type 1 X-Timestamp; or
     * timestamping individual reference data as used for complete
       validation.

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This form of eXtended validation data is called a Type 2 X-Timestamp.

NOTE:  The advantages/drawbacks for Type 1 and Type 2 X-Timestamp are
discussed in this document (see clause B.4.6.)

Internet Draft                             Electronic Signature Formats

If all the above conditions occur then a combination of the two formats
above may be used. This form of eXtended validation data is called
a X-Long-Timestamped.

Support for the extended forms of validation data is optional.

An Electronic Signature (ES) , with the additional validation data
forming the ES-X long is illustrated in Figure 2: 4:

+------------------------------------------------------- ES-X Long--+
|+--------------------------------------- EC-C --------+            |
||+---- Elect.Signature (ES)----+            +--------+| +--------+ |
|||+-------+-+-------+-+-------+| +---------+|Complete|| |Complete| |
||||Signa- | |Other  | |Digital|| |Timestamp||certi-  || |certi-  | |
||||ture   | |Signed | |Signa- || |over     ||ficate  || |ficate  | |
||||Policy | |Attri- | |ture   || |digital  ||and     || |and     | |
||||ID     | |butes  | |       || |signature||revoc.  || |revoc.  | |
|||+-------+ +-------+ +-------+| +---------+|refs    || |data    | |
||+-----------------------------+            +--------+| +--------+ |
|+-----------------------------------------------------+            |
+-------------------------------------------------------------------+

Figure 2: 4: Illustration of an ES and ES-X long.

An Electronic Signature (ES) , with the additional validation data
forming the eXtended Validation Data - Type 1 is illustrated in
Figure 3: 5:

+---------------------------------------------------------- ES-X 1 -+
|+---------------------------------------- EC-C --------+           |
|| +---- Elect.Signature (ES)----+            +--------+| +-------+ |
|| |+-------+ +-------+ +-------+| +---------+|Complete|| |       | |
|| ||Signa- | |Other  | |Digital|| |Timestamp||certifi-|| | Time- | |
|| ||ture   | |Signed | |Signa- || |over     ||cate and|| | stamp | |
|| ||Policy | |Attri- | |ture   || |digital  ||revoc.  || | over  | |
|| ||ID     | |butes  | |       || |signature||refs    || | CES   | |
|| |+-------+ +-------+ +-------+| +---------+|        || |       | |
|| +-----------------------------+            +--------+| +-------+ |
|+------------------------------------------------------+           |
+-------------------------------------------------------------------+

Figure 3: 5: Illustration of ES with ES-X Type 1

Internet Draft                             Electronic Signature Formats

An Electronic Signature (ES) , with the additional validation data
forming the eXtended Validation Data - Type 2 is illustrated in
Figure 4: 6:

+-------------------------------------------------------- ES-X 2 ---+
|+--------------------------------------- EC-C --------+            |
||+---- Elect.Signature (ES)----+            +--------+| +--------+ |
|||+-------+ +-------+ +-------+| +---------+|Complete|| |Times   | |
||||Signa- | |Other  | |Digital|| |Timestamp||certs   || |Stamp   | |
||||ture   | |Signed | |Signa- || |over     ||and     || |over    | |
||||Policy | |Attri- | |ture   || |digital  ||revoc.  || |Complete| |
||||ID     | |butes  | |       || |signature||refs    || |certs   | |
|||+-------+ +-------+ +-------+| +---------+|        || |and     | |
||+-----------------------------+            +--------+| |revoc.  | |
||                                                     | |refs    | |
|+-----------------------------------------------------+ +--------+ |
+-------------------------------------------------------------------+

Figure 4: 6: Illustration of ES with ES-X Type 2

2.7  Archive Validation Data

Before the algorithms, keys and other cryptographic data used at the
time the ES-C was built become weak and the cryptographic functions
become vulnerable, or the certificates supporting previous timestamps
expires, the signed data, the ES-C and any additional information
(ES-X) should be timestamped.  If possible this should use stronger
algorithms (or longer key lengths) than in the original timestamp.

This additional data and timestamp is called Archive Validation Data
(ES-A).  The Timestamping process may be repeated every time the
protection used to timestamp a previous ES-A become weak. An ES-A
may thus bear multiple embedded time stamps.

An example of an Electronic Signature (ES), with the additional
validation data for the ES-C and ES-X forming the ES-A is illustrated
in Figure 5. 7.

+-------------------------------- ES-A --------- ----------+
|  +-------------------- ES-A -----------------+           |
|  |  +--------- ES-X -------------- +         |           |
|  |  |..............................| +-----+ |  +-----+  |
|  |  |..............................| |Time | |  |Time |  |
|  |  |..............................| |Stamp| |  |Stamp|  |
|  |  |                              | +-----+ |  +-----+  |
|  |  +----------------------------- +         |           |
|  +-------------------------------------------+           |
+----------------------------------------------------------+

Figure 5: 7: Illustration of ES -A

Support for ES-A is optional.

Internet Draft                             Electronic Signature Formats

2.8  Arbitration

The ES-C may be used for arbitration should there be a dispute between
the signer and verifier, provided that:

      * a copy of the signature policy referenced by the signer is
        available;

      * the arbitrator knows where to retrieve the signer's certificate
        (if not already present), all the cross-certificates and the
        required CRLs and/or OCSPs responses referenced in the ES-C;

      * none of the issuing key from the certificate chain have ever
        been compromised;

      * the cryptography used at the time the ES-C was built has not
        been broken at the time the arbitration is performed.

When the second condition is not met, then the plaintiff must provide
an ES-X Long.

When it is known by some external means that the third condition is
not met, then the plaintiff must provide an ES-X Timestamped.

When the two previous conditions are not met, the plaintiff must
provide the two above information (i.e. an ES-X Timestamped and Long).

When the last condition is not met, the plaintiff must provide an
ES-A.

It should be noticed that a verifier may need to get two time stamps
at two different instants of time: one soon after the generation of
the ES and one soon after some grace period allowing any entity from
the certification chain to declare a key compromise.

2.9  Validation Process

The Validation Process validates an electronic signature in accordance
with the requirements of the signature policy. The output status of
the validation process can be:

     * valid;
     * invalid;
     * incomplete verification.

A Valid response indicates that the signature has passed verification
and it complies with the signature validation policy.

A signature validation policy is a part of the signature policy which
specifies the technical requirements on the signer in creating a
signature and verifier when validating a signature.

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An Invalid response indicates that either the signature format is
incorrect or that the digital signature value fails verification
(e.g. the integrity checks on the digital signature value fails or
any of the certificates on which the digital signature verification
depends is known to be invalid or revoked).

An Incomplete Validation response indicates that the format and
digital signature verifications have not failed but there is
insufficient information to determine if the electronic signature
is valid under the signature policy. This can include situations
where additional information, which does not effect the validity of
the digital signature value, may be available but is invalid.

In the case of Incomplete Validation, it may be possible to request
that the electronic signature be checked again at a later date when
additional validation information might become available. Also, in the
case of incomplete validation, additional information may be made
available to the application or user, thus allowing the application or
user to decide what to do with partially correct electronic signatures.

The validation process may also output validation data :

     * a signature timestamp;
     * the complete validation data;
     * the archive validation data.

2.10  Example Validation Sequence

As described earlier the signer or verifier may collect all the
additional data that forms the Electronic Signature.

Figure 6, 8, and subsequent description, describes how the validation
process may build up a complete electronic signature over time.

Soon after receiving the electronic signature (ES) from the signer (1),
the digital signature value may be checked,  the validation process
must at least add a time-stamp (2), unless the signer has provided one
which is trusted by the verifier. The validation process may also
validate the electronic signature, as required under the identified
signature policy, using additional data (e.g. certificates, CRL, etc.)
provided by trusted service providers. If the validation process is not
complete then the output from this stage is the ES-T.

When all the additional data (e.g. the complete certificate and
revocation information) necessary to validate the electronic signature
first becomes available, then the validation process:

     * obtains all the necessary additional certificate and revocation
       status information;

     * completes all the validation checks on the ES, using the
       complete certificate and revocation information  (if a timestamp
       is not already present, this may be added at the same stage
       combining ES-T and ES-C process);

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     * records the complete certificate and revocation references (3);

     * indicates the validity status to the user (4).

+---------------------------------------- ES-C ----------+
|+----------------------------- ES-T -------+            |
||+--- Elect.Signature (ES) ----+           | +--------+ |
|||+-------+ +-------+ +-------+|+---------+| |Complete| |
||||Signa- | |Other  | |Digital|||Timestamp|| |certifi-| |
||||ture   | |Signed | |Signa- |||over     || |cate and| |
||||Policy | |Attri- | |ture   |||digital  || |revoca- | |
||||ID     | |butes  | |       |||signature|| |tion    | |
|||+-------+ +-------+ +-------+|+---------+| |referen-| |
||+------------\----------------+    ^      | |ces     | |
||              \                    |      | +--------+ |
||               \ 1                /       |      ^     |
|+----------------\----------------/--------+      |     |
+------------------\--------------/-------------- /------+
                    \            /2    ----3-----/
 +----------+        |          /     /
 | Signed   |\       v         /     |
 |User data | \     +--------------------+     +------------+
 +----------+  \--->| Validation Process |---> |- Valid     |
                    +---|--^-------|--^--+ 4   |- Invalid   |
                        |  |       |  |        |- Validation|
                        v  |       v  |        |  Incomplete|
                    +---------+ +--------+     +------------+
                    |Signature| |Trusted |
                    | Policy  | |Service |
                    | Issuer  | |Provider|
                    +---------+ +--------+

Figure 6: 8: Illustration of an ES with Complete validation data (ES-C)

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At the same time as the validation process creates the ES-C, the
validation process may provide and/or record the values of certificates
and revocation status information used in ES-C, called the ES-X Long
(5). This is illustrated in figure 7: 9:

+---------------------------------------------------- ES-X ---------+
|+--------------------------------------- ES-C --------+ +--------+ |
||+--- Elect.Signature (ES) ----+           +--------+ | |Complete| |
|||+-------+ +-------+ +-------+|+---------+|Complete| | |certifi-| |
||||Signa- | |Other  | |Digital|||Timestamp||certifi-| | |cate    | |
||||ture   | |Signed | |Signa- |||over     ||cate and| | |and     | |
||||Policy | |Attri- | |ture   |||digital  ||revoca- | | |revoca- | |
||||ID     | |butes  | |       |||signature||tion    | | |tion    | |
|||+-------+ +---|---+ +-------+|+---------+|referen-| | |Data    | |
||+--------------\--------------+    ^      |ces     | | +--------+ |
||                \                  |      +--------+ |      ^     |
||                 \ 1             2/          ^       |      |     |
|+------------------\--------------/-----------|-------+     /      |
+--------------------\------------/-----------/-------------/-------+
                      \          /    ---3---/             /
 +----------+          |        /    /   -----------5-----/
 | Signed   |\         v       |     |  /
 |User data | \     +--------------------+     +-----------+
 +----------+  \--->| Validation Process |---> | - Valid   |
                    +---|--^-------|--^--+ 4   | - Invalid |
                        |  |       |  |        +-----------+
                        v  |       v  |
                    +---------+ +--------+
                    |Signature| |Trusted |
                    | Policy  | |Service |
                    | Issuer  | |Provider|
                    +---------+ +--------+

Figure 7: 9: Illustration ES with eXtended validation data (Long)

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When the validation process creates the ES-C it may also create
extended forms of validation data. A first alternative is to timestamp
all data forming the Type 1 X-Timestamp (6). This is illustrated in
figure 8: 10:

+---------------------------------------------------- ES-X -------+
|+--------------------------------------- ES-C --------+ +------+ |
||+--- Elect.Signature (ES) ----+           +--------+ | |Time- | |
|||+-------+ +-------+ +-------+|+---------+|Complete| | |stamp | |
||||Signa- | |Other  | |Digital|||Timestamp||certifi-| | |over  | |
||||ture   | |Signed | |Signa- |||over     ||cate and| | |CES   | |
||||Policy | |Attri- | |ture   |||digital  ||revoca- | | +------+ |
||||ID     | |butes  | |       |||signature||tion    | |     ^    |
|||+-------+ +--|----+ +-------+|+---------+|referen-| |     |    |
||+-------------|---------------+     ^     |ces     | |     |    |
||              |                     |     +--------+ |     |    |
||               \ 1                 2/        ^       |     |    |
|+----------------\------------------/---------|-------+     |    |
+------------------\----------------/----------/-------------/----+
                    \              /   ----3--/             /
 +----------+        |            /   /  --------------6---/
 | Signed   |\       v           |   |  /
 |User data | \     +--------------------+     +-----------+
 +----------+  \--->| Validation Process |---> | - Valid   |
                    +---|--^-------|--^--+ 4   | - Invalid |
                        |  |       |  |        +-----------+
                        v  |       v  |
                    +---------+ +--------+
                    |Signature| |Trusted |
                    | Policy  | |Service |
                    | Issuer  | |Provider|
                    +---------+ +--------+

Figure 8: 10: Illustration of ES with eXtended validation data - Type 1 X-
Timestamp

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Another alternative is to timestamp the certificate and revocation
information references used to validate the electronic signature (but
not the signature) (6'); this is called Type 2 X-Timestamped. This is
illustrated in figure 9: 11:

+---------------------------------------------------- ES-X ----------+
|+--------------------------------------- ES-C --------+ +---------+ |
||+--- Elect.Signature (ES) ----+           +--------+ | |Timestamp| |
|||+-------+ +-------+ +-------+|+---------+|Complete| | |over     | |
||||Signa- | |Other  | |Digital|||Timestamp||certifi-| | |Complete | |
||||ture   | |Signed | |Signa- |||over     ||cate and| | |Certifi- | |
||||Policy | |Attri- | |ture   |||digital  ||revoc.  | | |cate and | |
||||ID     | |butes  | |       |||signature||refs    | | |revoc.   | |
|||+-------+ +---^---+ +-------+|+----^----++---^----+ | |refs     | |
||+--------------\--------------+     |         |      | +---------+ |
|+----------------\------------------/----------|------+      ^      |
+----------------1-\----------------/----------/--------------|------+
                    \              /  -----3--/               |
 +----------+        |           2/  /   --------------6'-----/
 | Signed   |\       v           |  |   /
 |User data | \     +--------------------+     +-----------+
 +----------+  \--->| Validation Process |---> | - Valid   |
                    +---|--^-------|--^--+ 4   | - Invalid |
                        |  |       |  |        +-----------+
                        v  |       v  |
                    +---------+ +--------+
                    |Signature| |Trusted |
                    | Policy  | |Service |
                    | Issuer  | |Provider|
                    +---------+ +--------+

Figure 9: 11: Illustration of ES with eXtended validation data - Type 2 X-
Timestamp

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Before the algorithms used in any of electronic signatures become or
are likely, to be compromised or rendered vulnerable in the future, it
is necessary to timestamp the entire electronic signature, including
all the values of the validation and user data as an ES with Archive
validation data (ES-A)

  An ES-A is illustrated in figure 10: 12:

-------------------------------------------- ES-A --------------------+
----------------------------------------------------------------+     |
+------------------------------- EC-C --------++-----+          |     |
|                                             ||Time-|          |     |
|+-- Elect.Signature (ES) -+        +--------+||stamp|  +-------+     |
||+------++-------++-------|+------+|Complete|||over |  Complete|     |
|||Signa-||Other  ||Digital||Time- ||certifi-|||CES  |  |certi- |+----|
|||ture  ||Signed ||Signa- ||stamp ||cate and||+-----+  |ficate |Arch-|
|||Policy||Attri- ||ture   ||over  ||revoca- ||+------+ |and    |ive  |
|||ID    ||butes  ||       ||digit.||tion    |||Time- | |revoca-|Time |
||+------++---|---++-------||signa-||referen-|||stamp-| |tion   |stamp|
|+------------|------------+|ture  ||ces     |||over  | |data   |+----|
|             |             +------++--------+|Complete\+-------+  ^  |
|             |                ^         ^    ||cert.  |        |  |  |
+-------------|----------------|---------|----+|and rev|        |  |  |
               \               |         /     |refs.  |        |  |  |
                \              |        /      +-------+        |  |  |
-----------------\-------------|-------/------------------------+  |  |
+----------+      \            |      /                            /  |
| Signed   |       \2          |3    /     /--------------7-------/   |
|User data |        \          |    |     /                           |
+-------\--+         \         |    |    /                            |
---------\------------|--------|----|---/-----------------------------+
          \           v        |    |   |
          1\        +--------------------+     +-----------+
            \------>| Validation Process |---> | - Valid   |
                    +---|--^-------|--^--+ 4   | - Invalid |
                        |  |       |  |        +-----------+
                        v  |       v  |
                    +---------+ +--------+
                    |Signature| |Trusted |
                    | Policy  | |Service |
                    | Issuer  | |Provider|
                    +---------+ +--------+

Figure 10: 12: Illustration of an ES with Archive validation data (ES-A)

2.11  Additional optional features of an ES

This document also defines additional optional features of
an electronic signature to:

     * indicate a commitment type being made by the signer;
     * indicate the role under which a signature was created;
     * support multiple signatures.

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3. Data structure of an Electronic Signature

This clause uses and builds upon the Cryptographic Message Syntax
(CMS), as defined in RFC 2630 [CMS], and Enhanced Security Services
(ESS), as defined in RFC 2634 [ESS]. The overall structure
of Electronic Signature is as defined in [CMS]. The Electronic
Signature (ES) uses attributes defined in [CMS], [ESS] and
this document. This document defines in full the ES attributes which it
uses and are not defined elsewhere.

The mandated set of attributes and the digital signature value is
defined as the minimum Electronic Signature (ES) required by this
document. A signature policy MAY mandate other signed attributes to be
present.

3.1  General Syntax

The general syntax of the ES is as defined in [CMS].

3.2  Data Content Type

The data content type of the ES is as defined in [CMS].

The data content type is intended to refer to arbitrary octet strings,
such as ASCII text files; the interpretation is left to the
application.  Such strings need not have any internal structure
(although they could have their own ASN.1 definition or other
structure).

3.3  Signed-data Content Type

The Signed-data content type of the ES is as defined in [CMS].

The signed-data content type consists of a content of any type and zero
or more signature values. Any number of signers in parallel can sign
any type of content. The typical application of the signed-data content
type represents one signer's digital signature on content of the data
content type.

To make sure that the verifier uses the right certificate, this
document mandates that the hash of the signers certificate is always
included in the Signing Certificate signed attribute.

3.4  SignedData Type

The syntax of the SignedData type of the ES is as defined in [CMS].

The fields of type SignedData have the meanings defined [CMS] except
that:

     * version is the syntax version number. The value of version must
       be 3.

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     * The identification of signer's certificate used to create the
       signature is always present as a signed attribute.

     * The degenerate case where there are no signers is not valid in
       this document.

3.5  EncapsulatedContentInfo Type

The syntax of the EncapsulatedContentInfo a type of the ES is as
defined in [CMS].

For the purpose of long term validation as defined by this document, it
is advisable that either the eContent is present, or the data which is
signed is archived in such as way as to preserve the any data encoding.
It is important that the OCTET STRING used to generate the signature
remains the same every time either the verifier or an arbitrator
validates the signature.

The degenerate case where there are no signers is not valid in this
document.

3.6  SignerInfo Type

The syntax of the SignerInfo a type of the ES is as defined in [CMS].

Per-signer information is represented in the type SignerInfo. In the
case of multiple independent signatures, there is an instance
of this field for each signer.

The fields of type SignerInfo have the meanings defined in [CMS]
except that signedAttributes must, as a minimum, contain the following
attributes:

* ContentType as defined in clause 3.7.1.
* MessageDigest as defined in clause 3.7.2.
* SigningTime as defined in clause 3.7.3.
* SigningCertificate as defined in clause 3.8.1.
* SignaturePolicyId as defined in clause 3.9.1.

3.6.1  Message Digest Calculation Process

The message digest calculation process is as defined in [CMS].

3.6.2  Message Signature Generation Process

The input to the digital signature generation process is as defined in
[CMS].

3.6.3  Message Signature Verification Process

The procedures for CMS signed data validation are as defined in
[CMS] and enhanced in this document.

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The input to the signature verification process includes the signer's
public key verified as correct using either the ESS Signing
Certificate attribute or the Other Signing Certificate attribute.

3.7  CMS Imported Mandatory Present Attributes

The following attributes MUST be present with the signed-data defined
by this document. The attributes are defined in [CMS].

3.7.1  Content Type

The syntax of the content-type attribute type of the ES is as defined
in [CMS].

3.7.2  Message Digest

The syntax of the message-digest attribute type of the ES is as defined
in [CMS].

3.7.3  Signing Time

The syntax of the message-digest attribute type of the ES is as defined
in [CMS] and further qualified by this document.

The signing-time attribute type specifies the time at which the signer
claims to have performed the signing process.

This present document recommends the use of GeneralizedTime.

3.8  Alternative Signing Certificate Attributes

One, and only one, of the following two alternative attributes MUST be
present with the signed-data defined by this document to identify the
signing certificate. Both attributes include an identifier and a hash
of the signing certificate. The first, which is adopted in existing
standards, may be only used with the SHA-1 hashing algorithm. The
other shall be used when other hashing algorithms are to be supported.

The signing certificate attribute is designed to prevent the simple
substitution and re-issue attacks, and to allow for a restricted set of
authorization certificates to be used in verifying a signature.

3.8.1  ESS Signing Certificate Attribute Definition

The syntax of the signing certificate attribute type of the ES is as
defined in [ESS], and further qualified and profile in this document.

The ESS signing certificate attribute must be a signed attribute.

This document mandates the presence of this attribute as a signed CMS
attribute, and the sequence must not be empty. The certificate used to
verify the signature must be identified in the sequence, the Signature
Validation Policy may mandate other certificate references to be
present, that may include all the certificates up to the point of

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trust. The encoding of the ESSCertID for this certificate must include
the issuerSerial field.

The issuerAndSerialNumber present in the SignerInfo must be
consistent with issuerSerial field. The certificate identified must be
used during the signature verification process. If the hash of the
certificate does not match the certificate used to verify the
signature, the signature must be considered invalid.

The sequence of policy information field is not used in this document.

NOTE: Where an attribute certificate is used by the signer to associate
a role, or other attributes of the signer, with the electronic
signature this is placed in the Signer Attribute attribute as defined
in clause 3.12.3.

3.8.2  Other Signing Certificate Attribute Definition

The following attribute is identical to the ESS SigningCertificate
defined above except that this attribute can be used with hashing
algorithms other than SHA-1.

This attribute must be used in the same manner as defined above for
the ESS SigningCertificate attribute.

The following object identifier identifies the signing certificate
attribute:

id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-aa(2) 19 }

The signing certificate attribute value has the ASN.1 syntax
OtherSigningCertificate

OtherSigningCertificate ::=  SEQUENCE {
    certs        SEQUENCE OF OtherCertID,
    policies     SEQUENCE OF PolicyInformation OPTIONAL
                 -- NOT USED IN THIS DOCUMENT
}

OtherCertID ::= SEQUENCE {
     otherCertHash            OtherHash,
     issuerSerial             IssuerSerial OPTIONAL
}

OtherHash ::= CHOICE {
    sha1Hash OtherHashValue,  -- This contains a SHA-1 hash
    otherHash OtherHashAlgAndValue
}

OtherHashValue ::= OCTET STRING

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OtherHashAlgAndValue ::= SEQUENCE {
  hashAlgorithm  AlgorithmIdentifier,
  hashValue      OtherHashValue
}

3.9  Additional Mandatory Attributes

3.9.1  Signature policy Identifier

This document mandates that a reference to the signature policy, which is
included in the signedData, this reference is either explicitly
identified or implied by the semantics of the signed content and other
external data.  A signature policy defines the rules for creation and
validation of an electronic signature, is included as a signed
attribute with every signature. The signature policy identifier must be
a signed attribute.

The following object identifier identifies the signature policy
identifier attribute:

id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-aa(2) 15 }

Signature-policy-identifier attribute values have ASN.1 type
SignaturePolicyIdentifier.

SignaturePolicyIdentifier ::= CHOICE{
         SignaturePolicyId          SignaturePolicyId,
         SignaturePolicyImplied     SignaturePolicyImplied }

SignaturePolicyId ::= SEQUENCE {
        sigPolicyIdentifier   SigPolicyId,
        sigPolicyHash         SigPolicyHash,
        sigPolicyQualifiers   SEQUENCE SIZE (1..MAX) OF
                              SigPolicyQualifierInfo      OPTIONAL
										}

SignaturePolicyImplied ::= NULL

The sigPolicyIdentifier presence of the NULL type indicates that the signature policy is
implied by the semantics of the signed data and other external data.

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The sigPolicyId field contains an object-identifier which
uniquely identifies a specific version of the signature policy. The
syntax of this field is as follows:

   SigPolicyId ::= OBJECT IDENTIFIER

The sigPolicyHash field contains the identifier of the hash algorithm
and the hash of the value of the signature policy.

If the signature policy is defined using a computer processable
notation like ASN.1, then the hash is calculated on the value without
the outer type and length fields and the hashing algorithm must be as
specified in the field signPolicyHshAlg.

If the signature policy is defined using another structure, the type of
structure and the hashing algorithm must be either specified as part
of the signature policy, or indicated using a signature policy
qualifier.

   SigPolicyHash ::= ETSIHashAlgAndValue

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A signature policy identifier may be qualified with other information
about the qualifier. The semantics and syntax of the qualifier is as
associated with the object-identifier in the sigPolicyQualifierId
field. The general syntax of this qualifier is as follows:

   SigPolicyQualifierInfo ::= SEQUENCE {
        sigPolicyQualifierId  SigPolicyQualifierId,
        sigQualifier          ANY DEFINED BY sigPolicyQualifierId
}

This document specifies the following qualifiers:

    * spuri: This contains the web URI or URL reference to the
      signature policy

    * spUserNotice: This contains a user notice which should be
      displayed whenever the signature is validated.

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-- sigpolicyQualifierIds defined in this document

SigPolicyQualifierId ::=  OBJECT IDENTIFIER

    id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-spq(5) 1 }

   SPuri ::= IA5String

    id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-spq(5) 2 }

   SPUserNotice ::= SEQUENCE {
        noticeRef        NoticeReference OPTIONAL,
        explicitText     DisplayText OPTIONAL
}

   NoticeReference ::= SEQUENCE {
        organization     DisplayText,
        noticeNumbers    SEQUENCE OF INTEGER
}

   DisplayText ::= CHOICE {
        visibleString    VisibleString  (SIZE (1..200)),
        bmpString        BMPString      (SIZE (1..200)),
        utf8String       UTF8String     (SIZE (1..200))
}

3.10  CMS Imported Optional Attributes

The following attributes MAY be present with the signed-data defined by
this document. The attributes are defined in ref [CMS] and are imported

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into this specification and were appropriate qualified and profiling by
this document.

3.10.1  Countersignature

The syntax of the countersignature attribute type of the ES is as
defined in [CMS]. The countersignature attribute must be an unsigned
attribute.

3.11  ESS Imported Optional Attributes

The following attributes MAY be present with the signed-data defined by
this document. The attributes are defined in ref [ESS] and are imported
into this specification and were appropriate qualified and profiling
by this document.

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3.11.1 Content Reference Attribute

The content reference attribute is a link from one SignedData to
another. It may be used to link a reply to the original message to
which it refers, or to incorporate by reference one SignedData into
another.

The content reference attribute MUST be used as defined in [ESS].  The
content reference MUST be a signed attribute.

The syntax of the content reference attribute type of the ES is as
defined in [ESS].

3.11.2  Content Identifier Attribute

The content identifier attribute provides an identifier for the signed
content for use when reference may be later required to that content,
for example in the content reference attribute in other signed data
sent later.

The content identifier must be a signed attribute.

The syntax of the content identifier attribute type of the ES is as
defined in [ESS].

The minimal signedContentIdentifier should contain a concatenation of
user-specific identification information (such as a user name or public
keying material identification information), a GeneralizedTime string,
and a random number.

3.12   Additional Optional Attributes

3.12.1  Commitment Type Indication

3.11.3	Content Hints Attribute

There

The content hints attribute provides information that describes the
format of the signed content. It may be situation were a used by the signer wants to explicitly indicate
to a verifier the precise format that by signing MUST be used to present the data, it illustrates data
(e.g. text, voice, video) to a type of commitment
on behalf of the signer. The commitmentTypeIndication attribute conveys
such information.

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The commitmentTypeIndication verifier.  This attribute must MUST be a
present when it is mandatory to present the signed attribute. data to human users
on verification.

The commitment syntax of the content hints attribute type may be:

    * defined as part of the signature policy, ES is as defined
in which case ESS (RFC 2634, section 2.9 [9]).

When used to indicate the
      commitment type has precise semantics that is defined as part format of the signature policy.

    * data to be a registered type, in presented to
the user the following rules apply:

The contentType (defined in RFC 2630 [8]) indicates the type of the
associated content. It is an object identifier (i.e. a unique string of
integers) assigned by an authority that defines the content type.

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The UTF8String shall define the presentation format. The format may be
defined by MIME types as indicated below.

Note 1: The contentType can be id-data defined in CMS (RFC 2630 [8]).
The UTF8String can be used to indicate the encoding of the data, like
MIME type. RFC 2045 [25] provides a common structure for encoding a
range of electronic documents and other multi-media types, see annex B
for further information, a system supporting verification of electronic
signature may present information to users in the form identified by
the MIME type.

id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs7(7) 1 }

3.12   Additional Optional Attributes

3.12.1  Commitment Type Indication Attribute

There may be situation were a signer wants to explicitly indicate to a
verifier that by signing the data, it illustrates a type of commitment
on behalf of the signer. The commitmentTypeIndication attribute conveys
such information.

The commitmentTypeIndication attribute must be a signed attribute.

The commitment type may be:

    * defined as part of the signature policy, in which case the
      commitment type has precise semantics that is defined as part of
      the signature policy.

    * be a registered type, in which case the commitment type has
      precise semantics defined by registration, under the rules of the
      registration authority. Such a registration authority may be a
      trading association or a legislative authority.

The signature policy specifies a set of attributes that it
"recognizes". This "recognized" set includes all those commitment types
defined as part of the signature policy as well as any externally
defined commitment types that the policy may choose to recognize. Only
recognized commitment types are allowed in this field.

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The following object identifier identifies the commitment type
indication attribute:

id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}

Commitment-Type-Indication attribute values have ASN.1 type
CommitmentTypeIndication.

CommitmentTypeIndication ::= SEQUENCE {
   commitmentTypeId            CommitmentTypeIdentifier,
   commitmentTypeQualifier     SEQUENCE SIZE (1..MAX) OF
                               CommitmentTypeQualifier      OPTIONAL
}

CommitmentTypeIdentifier ::= OBJECT IDENTIFIER

CommitmentTypeQualifier ::= SEQUENCE {
    commitmentTypeIdentifier   CommitmentTypeIdentifier,
    qualifier                  ANY DEFINED BY
                               commitmentTypeIdentifier
}

The use of any qualifiers to the commitment type is outside the scope
of this document.

The following generic commitment types are defined in this document:

       id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-
       body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
       cti(6) 1}

       id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-
       body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
       cti(6) 2}

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       id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1)
       member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
       smime(16) cti(6) 3}

       id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-
       body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
       cti(6) 4}

       id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1)
       member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
       smime(16) cti(6) 5}

       id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1)
       member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
       smime(16) cti(6) 6}

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These generic commitment types have the following meaning:

Proof of origin indicates that the signer recognizes to have created,
approved and sent the message.

Proof of receipt indicates that signer recognizes to have received the
content of the message.

Proof of delivery indicates that the TSP providing that indication has
delivered a message in a local store accessible to the recipient of the
message.

Proof of sender indicates that the entity providing that indication has
sent the message (but not necessarily created it).

Proof of approval indicates that the signer has approved the content of
the message.

Proof of creation indicates that the signer has created the message
(but not necessarily approved, nor sent it).

3.12.2  Signer Location attribute

The signer-location attribute is an attribute which specifies a
mnemonic for an address associated with the signer at a particular
geographical (e.g. city) location. The mnemonic is registered in the
country in which the signer is located and is used in the provision of
the Public Telegram Service (according to ITU-T Recommendation F.1
[PTS]).

The signer-location attribute must be a signed attribute.

The following object identifier identifies the signer-location
attribute:

id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}

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Signer-location attribute values have ASN.1 type SignerLocation.

   SignerLocation ::= SEQUENCE {
        -- at least one of the following must be present
      countryName          [0] DirectoryString      OPTIONAL,
        -- as used to name a Country in X.500
      localityName         [1] DirectoryString      OPTIONAL,
         -- as used to name a locality in X.500
      postalAdddress       [2] PostalAddress        OPTIONAL
}

   PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString

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3.12.3  Signer Attributes attribute

The signer-attributes attribute is an attribute which specifies
additional attributes of the signer (e.g. role).

It may be either:

     * claimed attributes of the signer; or
     * certified attributes of the signer;

The signer-attributes attribute must be a signed attribute.

The following object identifier identifies the signer-attribute
attribute:

id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}

signer-attribute attribute values have ASN.1 type SignerAttribute.

   SignerAttribute ::= SEQUENCE OF CHOICE {
      claimedAttributes      [0]  ClaimedAttributes,
      certifiedAttributes    [1]  CertifiedAttributes
}

ClaimedAttributes ::= SEQUENCE OF Attribute

CertifiedAttributes ::= AttributeCertificate
         -- as defined in X.509 : see section 10.3

NOTE:  The claimed and certified attribute are imported from ITU-T
Recommendations X.501 [16] and ITU-T Recommendation X.509 : Draft
Amendment on Certificate Extensions, October 1999.

3.12.4  Content Timestamp attribute

The content timestamp attribute is an attribute which is the timestamp
of the signed data content before it is signed.

The content timestamp attribute must be a signed attribute.

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The following object identifier identifies the signer-attribute
attribute:

     id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1)
     member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
     smime(16) id-aa(2) 20}

Content timestamp attribute values have ASN.1 type ContentTimestamp:
ContentTimestamp::= TimeStampToken

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The value of messageImprint field within TimeStampToken must be a hash
of the value of eContent field within encapContentInfo within the
signedData.

For further information and definition of TimeStampToken see [TSP].

3.13  Support for Multiple Signatures

3.13.1  Independent Signatures

Multiple independent signatures are supported by independent SignerInfo
from each signer.

Each SignerInfo must include all the attributes required under this
document and must be processed independently by the verifier.

3.13.2  Embedded Signatures

Multiple embedded signatures are supported using the counter-signature
unsigned attribute (see clause 3.10.1). Each counter signature is
carried in Countersignature held as an unsigned attribute to the
SignerInfo to which the counter-signature is applied.

4.  Validation Data

This clause specifies the validation data structures which builds on
the electronic signature specified in clause 3. This includes:

    * Timestamp applied to the electronic signature value.

    * Complete validation data which comprises the timestamp of the
      signature value, plus references to all the certificates and
      revocation information used for full validation of the electronic
      signature.

The following optional eXtended forms of validation data are also
defined:

     * X-timestamp: There are two types of timestamp used in extended
       validation data defined by this document.

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        - Type 1 -Timestamp which comprises a timestamp over the ES
          with Complete validation data (ES-C).

        - Type 2 X-Timestamp which comprises of a timestamp over the
          certification path references and the revocation information
          references used to support the ES-C.

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               * X-Long : This comprises a  Complete validation data
                 plus the actual values of all the certificates and
                 revocation information used in the ES-C.

               * X-Long-Timestamp: This comprises a Type 1 or Type 2
                 X-Timestamp plus the actual values of all the
                 certificates and revocation information used in the
                 ES-C.

This clause also specifies the data structures used in Archive
validation data:

      * Archive validation data comprises a  Complete validation data,
        the certificate and revocation values (as in a X-Long
        validation data), any other existing X-timestamps, plus the
        Signed User data and an additional archive timestamp over all
        that data. An archive timestamp may be repeatedly applied
        after long periods to maintain validity when electronic
        signature and timestamping algorithms weaken.

The additional data required to create the forms of electronic
signature identified above is carried as unsigned attributes
associated with an individual signature by being placed in the
unsignedAttrs field of SignerInfo. Thus all the attributes defined
in clause 4 are unsigned attributes.

NOTE:  Where multiple signatures are to be supported, as described in
clause 3.13, each signature has a separate SignerInfo. Thus, each
signature requires its own unsigned attribute values to create ES-T,
ES-C etc.

4.1  Electronic Signature Timestamp

An Electronic Signature with Timestamp is an Electronic Signature for
which part, but not all, of the additional data required for validation
is available (e.g. some certificates and revocation information is
available but not all).

The minimum structure Timestamp validation data is the Signature
Timestamp Attribute as defined in clause 4.1.1 over the ES signature
value.

4.1.1  Signature Timestamp Attribute Definition

The Signature Timestamp attribute is timestamp of the signature value.
It is an unsigned attribute. Several instances of this attribute from
different TSAs may occur with an electronic signature.

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The Signature Validation Policy specifies, in the
signatureTimestampDelay field of TimestampTrustConditions, a maximum
acceptable time difference which is allowed between the time indicated
in the signing time attribute and the time indicated by the Signature
Timestamp attribute. If this delay is exceeded then the electronic
signature must be considered as invalid.

The following object identifier identifies the Signature Timestamp
attribute:

     id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1)
     member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
     id-aa(2) 14}

The Signature timestamp attribute value has ASN.1 type
SignatureTimeStampToken.

SignatureTimeStampToken ::= TimeStampToken

The value of messageImprint field within TimeStampToken must be a hash
of the value of signature field within SignerInfo for the signedData
being timestamped.

For further information and definition of TimeStampToken see [TSP]

4.2  Complete Validation Data

An electronic signature with complete validation data is an Electronic
Signature for which all the additional data required for validation
(i.e. all certificates and revocation information) is available.
Complete validation data (ES-C) build on the electronic signature
Timestamp as defined above.

The minimum structure of a Complete validation data is:

     * the Signature Timestamp Attribute, as defined in clause 4.1.1;
     * Complete Certificate Refs, as defined in clause 4.2.1;
     * Complete Revocation Refs, as defined in clause 4.2.2.

The Complete validation data MAY also include the following additional
information, forming a X-Long validation data, for use if later
validation processes may not have access to this information:

     * Complete Certificate Values, as defined in clause 4.2.3;
     * Complete Revocation Values, as defined in clause 4.2.4.

The  Complete validation data MAY also include one of the following
additional attributes, forming a X-Timestamp validation data, to
provide additional protection against later CA compromise and provide
integrity of the validation data used:

     * ES-C Timestamp, as defined in clause 4.2.5; or
     * Time-Stamped Certificates and CRLs references, as defined in
       clause 4.2.6.

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NOTE 1: As long as the CA's are trusted such that these keys cannot
be compromised or the cryptography used broken, the ES-C provides long
term proof of a valid electronic signature.

A valid electronic signature is an electronic signature which passes
validation according to a signature validation policy.

NOTE 2: The ES-C provides the following important property for long
standing signatures; that is having been found once to be valid, must
continue to be so months or years later. Long after the validity period
of the certificates have expired, or after the user key has been
compromised.

4.2.1  Complete Certificate Refs Attribute Definition

The Complete Certificate Refs attribute is an unsigned attribute. It
references the full set of CA certificates that have been used to
validate a ES with Complete validation data (ES-C) up to (but not
including) the signer's certificate. Only a single instance of this
attribute must occur with an electronic signature.

Note: The signer's certified is referenced in the signing certificate
attribute (see clause 3.1).

id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}

The complete certificate refs attribute value has the ASN.1 syntax
CompleteCertificateRefs.

CompleteCertificateRefs ::=  SEQUENCE OF OTHERCertID

OTHERCertID is defined in clause 3.8.2.

The IssuerSerial that must be present in OTHERCertID. The certHash
must match the hash of the certificate referenced.

NOTE:  Copies of the certificate values may be held using the
Certificate Values attribute defined in clause 4.3.1.

4.2.2  Complete Revocation Refs Attribute Definition

The Complete Revocation Refs attribute is an unsigned attribute. Only a
single instance of this attribute must occur with an electronic
signature. It references the full set of the CRL or OCSP responses that
have been used in the validation of the signer and CA certificates
used in ES with Complete validation data.

The following object identifier identifies the CompleteRevocationRefs
attribute:

id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}

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The complete revocation refs attribute value has the ASN.1 syntax
CompleteRevocationRefs.

CompleteRevocationRefs ::=  SEQUENCE OF CrlOcspRef

CrlOcspRef ::= SEQUENCE {
    crlids           [0] CRLListID        OPTIONAL,
    ocspids          [1] OcspListID       OPTIONAL,
    otherRev         [2] OtherRevRefs     OPTIONAL
}

CompleteRevocationRefs must contain one CrlOcspRef for the signing
certificate, followed by one for each OTHERCertID in the
CompleteCertificateRefs attribute. The second and subsequent CrlOcspRef
fields must be in the same order as the OTHERCertID to which they
relate. At least one of CRLListID or OcspListID or OtherRevRefs should
be present for all but the "trusted" CA of the certificate path.

CRLListID ::=  SEQUENCE {
    crls        SEQUENCE OF CrlValidatedID}

CrlValidatedID ::=  SEQUENCE {
     crlHash                   ETSIHash,
     crlIdentifier             CrlIdentifier OPTIONAL}

CrlIdentifier ::= SEQUENCE {
    crlissuer                 Name,
    crlIssuedTime             UTCTime,
    crlNumber                 INTEGER OPTIONAL
                                            }

OcspListID ::=  SEQUENCE {
    ocspResponses        SEQUENCE OF OcspResponsesID}

OcspResponsesID ::=  SEQUENCE {
    ocspIdentifier              OcspIdentifier,
    ocspRepHash                 ETSIHash    OPTIONAL
                                            }

OcspIdentifier ::= SEQUENCE {
     ocspResponderID    ResponderID,
                       -- As in OCSP response data
     producedAt      GeneralizedTime
                       -- As in OCSP response data
                                             }

When creating an crlValidatedID, the crlHash is computed over the
entire DER encoded CRL including the signature. The crlIdentifier would
normally be present unless the CRL can be inferred from other
information.

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The crlIdentifier is to identify the CRL using the issuer name and the
CRL issued time which must correspond to the time "thisUpdate"
contained in the issued CRL. The crlListID attribute is an unsigned
attribute. In the case that the identified CRL is a Delta CRL then
references to the set of CRLs to provide a complete revocation list
must be included.

The OcspIdentifier is to identify the OSCP response using the issuer
name and the time of issue of the OCSP response which must correspond
to the time "producedAt" contained in the issued OCSP response. Since
it may be needed to make the difference between two OCSP responses
received within the same second, then the hash of the response
contained in the OcspResponsesID may be needed to solve the ambiguity.

NOTE: Copies of the CRL and OCSP responses values may be held using
the Revocation Values attribute defined in clause 4.3.2.

OtherRevRefs ::= SEQUENCE {
   otherRevRefType      OtherRevRefType,
   otherRevRefs         ANY DEFINED BY otherRevRefType
}

OtherRevRefType ::= OBJECT IDENTIFIER

The syntax and semantics of other revocation references is outside the
scope of this document.  The definition of the syntax of the other form
of revocation information is as identified by OtherRevRefType.

4.3  Extended Validation Data

4.3.1  Certificate Values Attribute Definition

The Certificate Values attribute is an unsigned attribute. Only a
single instance of this attribute must occur with an electronic
signature. It holds the values of certificates referenced in the
CompleteCertificateRefs attribute.

Note: If an Attribute Certificate is used, it is not provided in this
structure but must be provided by the signer as a signer-attributes
attribute (see clause 12.3).

The following object identifier identifies the CertificateValues
attribute:

id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}

The certificate values attribute value has the ASN.1 syntax
CertificateValues.

CertificateValues ::=  SEQUENCE OF Certificate

Certificate is defined in RFC2459 and ITU-T Recommendation X.509 [1])

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4.3.2  Revocation Values Attribute Definition

The Revocation Values attribute is an unsigned attribute. Only a single
instance of this attribute must occur with an electronic signature. It
holds the values of CRLs and OCSP referenced in the
CompleteRevocationRefs attribute.

The following object identifier identifies the Revocation Values
attribute:

    id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 24}

The revocation values attribute value has the ASN.1 syntax
RevocationValues.

RevocationValues ::=  SEQUENCE {
   crlVals           [0] SEQUENCE OF CertificateList     OPTIONAL,
   ocspVals          [1] SEQUENCE OF BasicOCSPResponse   OPTIONAL,
   otherRevVals      [2] OtherRevVals
}

OtherRevVals ::= SEQUENCE {
   otherRevValType       OtherRevValType,
   otherRevVals          ANY DEFINED BY otherRevValType
}

OtherRevValType ::= OBJECT IDENTIFIER

The syntax and semantics of the other revocation values is outside the
scope of this document. The definition of the syntax of the other form
of revocation information is as identified by OtherRevRefType.

CertificateList is defined in RFC 2459 [RFC2459] and in ITU-T
Recommendation X.509 [X509]).

BasicOCSPResponse is defined in RFC 2560 [OCSP].

4.3.3  ES-C Timestamp Attribute Definition

This attribute is used for the Type 1 X-Timestamped validation data.
The ES-C Timestamp attribute is an unsigned attribute. It is timestamp
of a hash of the electronic signature and the complete validation data
(ES-C). It is a special purpose TimeStampToken Attribute which
timestamps the ES-C. Several instances instance of this attribute may
occur with an electronic signature from different TSAs.

The following object identifier identifies the ES-C Timestamp
attribute:

    id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 25}

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The ES-C timestamp attribute value has the ASN.1 syntax
ESCTimeStampToken.

ESCTimeStampToken ::= TimeStampToken

The value of messageImprint field within TimeStampToken must be a hash
of the concatenated values (without the type or length encoding for
that value) of the following data objects as present in the ES with
Complete validation data (ES-C):

     * signature field within SignerInfo;

     * SignatureTimeStampToken attribute;

     * CompleteCertificateRefs attribute;

     * CompleteRevocationRefs attribute.

For further information and definition of the Time Stamp Token see
[TSP].

4.3.4  Time-Stamped Certificates and CRLs Attribute Definition

This attribute is used for the Type 2 X-Timestamp validation data. A
TimestampedCertsCRLsRef attribute is an unsigned attribute. It is a
list of referenced certificates and OCSP responses/CRLs which are been
timestamped to protect against certain CA compromises. Its syntax is as
follows:

The following object identifier identifies the TimestampedCertsCRLsRef
attribute:

    id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 26}

The attribute value has the ASN.1 syntax TimestampedCertsCRLs.

TimestampedCertsCRLs ::= TimeStampToken

The value of messageImprint field within TimeStampToken must be a hash
of the concatenated values (without the type or length encoding for
that value) of the following data objects as present in the ES with
Complete validation data (ES-C):

* CompleteCertificateRefs attribute;
* CompleteRevocationRefs attribute.

4.4  Archive Validation Data

Where an electronic signature is required to last for a very long time,
and a the timestamp on an electronic signature is in danger of being
invalidated due to algorithm weakness or limits in the validity period
of the TSA certificate, then it may be required to timestamp the

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electronic signature several times. When this is required an archive
timestamp attribute may be required. This timestamp may be repeatedly
applied over a period of time.

4.4.1  Archive Timestamp Attribute Definition

The Archive Timestamp attribute is timestamp of the user data and the
entire electronic signature. If the Certificate values and Revocation
Values attributes are not present these attributes must be added to
the electronic signature prior to the timestamp. The Archive Timestamp
attribute is an unsigned attribute. Several instances of this attribute
may occur with on electronic signature both over time and from
different TSAs.

The following object identifier identifies the Nested Archive Timestamp
attribute:

    id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 27}

Archive timestamp attribute values have the ASN.1 syntax
ArchiveTimeStampToken

ArchiveTimeStampToken ::= TimeStampToken

The value of messageImprint field within TimeStampToken must be a hash
of the concatenated values (without the type or length encoding for
that value) of the following data objects as present in the electronic
signature:

     * encapContentInfo eContent OCTET STRING;
     * signedAttributes;
     * signature field within SignerInfo;
     * SignatureTimeStampToken attribute;
     * CompleteCertificateRefs attribute;
     * CompleteRevocationData attribute;
     * CertificateValues attribute
       (If not already present this information must be included in
       the ES-A);
     * RevocationValues attribute
       (If not already present this information must be included in
       the ES-A);
     * ESCTimeStampToken attribute if present;
     * TimestampedCertsCRLs attribute if present;
     * any previous ArchiveTimeStampToken attributes.

For further information and definition of TimeStampToken see [TSP]

The timestamp should be created using stronger algorithms (or longer
key lengths) than in the original electronic signatures.

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5.  Security considerations

5.1  Protection of Private Key

The security of the electronic signature mechanism defined in this
document depends on the privacy of the signer's private key.
Implementations must take steps to ensure that private keys cannot be
compromised.

5.2  Choice of Algorithms

Implementers should be aware that cryptographic algorithms become
weaker with time. As new cryptoanalysis techniques are developed and
computing performance improves, the work factor to break a particular
cryptographic algorithm will reduce. Therefore, cryptographic algorithm
implementations should be modular allowing new algorithms to be readily
inserted. That is, implementers should be prepared for the set of
mandatory to implement algorithms to change over time.

6.  Conformance Requirements

This document only defines conformance requirements up to a ES with
Complete validation data (ES-C). This means that none of the extended
and archive forms of Electronic Signature (ES-X, ES-A) need to be
implemented to get conformance to this standard.

This document mandates support for elements of the signature policy.

6.1  Signer

A system supporting signers according to this document must, at a
minimum, support generation of an electronic signature consisting of
the following components:

      * The general CMS syntax and content type as defined in RFC 2630
        (see clauses 4.1 and 4.2).

      * CMS SignedData as defined in RFC 2630 with version set to 3
        and at least one SignerInfo must be present
        (see clauses 4.3, 4.4, 4.5, 4.6).

      * The following CMS Attributes as defined in RFC 2630 :

             - ContentType; This must always be present
               (see clause 3.7.1);

             - MessageDigest; This must always be present
               (see clause 3.7.2);

             - SigningTime; This must always be present
               (see clause 3.7.3).

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      * The following ESS Attributes as defined in RFC 2634 :

              - SigningCertificate: This must be set as defined
                in clauses 3.8.1 and 3.8.2.

      * The following Attributes as defined in clause 3.9:
             - SignaturePolicyIdentifier; This must always be present.

      * Public Key Certificates as defined in ITU-T Recommendation
        X.509 [1] and profiled in RFC 2459 [7] (see clause 9.1).

6.2  Verifier using timestamping

A system supporting verifiers according to this document with
timestamping facilities must, at a minimum, support:

       * Verification of the mandated components of an electronic
         signature, as defined in clause 14.1. 5.1.

       * Signature Timestamp attribute, as defined in clause 4.1.1.

       * Complete Certificate Refs attribute, as defined in
         clause 4.2.1.

       * Complete Revocation Refs Attribute, as defined in
         clause  4.2.2.

       * Public Key Certificates, as defined in ITU-T
         Recommendation X.509 and profiled in RFC 2459.

       * Either of:

             - Certificate Revocation Lists. as defined in ITU-T
               Recommendation X.509 [1] and profiled in RFC 2459 [7];
               or

             - On-line Certificate Status Protocol responses, as
               defined in RFC 2560.

6.3	Verifier using secure records

A system supporting verifiers according to the present document shall,
at a minimum, support:

       * Verification of the mandated components of an electronic
         signature, as defined in subclause 5.1.

       * Complete Certificate Refs attribute, as defined in
          subclause 4.2.1.

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       * Complete Revocation Refs Attribute, as defined in
         subclause 9.2.2.

       * A record shall be maintained, which cannot be undetectably
         modified, of the electronic signature and the time when the
         signature was first validated using the referenced
         certificates and revocation information.

       * Public Key Certificates, as defined in ITU-T Recommendation
         X.509 [1] and profiled in RFC 2459 [7] (see subclause 10.1).

       * Either of:
             - Certificate Revocation Lists. as defined in ITU-T
               Recommendation X.509 [1] and profiled in RFC 2459 [7]
              Or

             - On-line Certificate Status Protocol, as defined
               in RFC 2560 [8] (see subclause 10.3).

7. References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[ESS] P. Hoffman, "Enhanced Security Services for S/MIME",

[CMS] R. Housley, "Cryptographic Message Syntax", RFC 2630,
June 1999.

[OCSP] M. Myers, R. Ankney, A. Malpani, S. Galperin, C. Adams.
On-line Status Certificate Protocol, RFC 2560.

[TSP] C. Adams, P. Cain, D. Pinkas, R. Zuccherato. Time Stamp Protocol
(TSP), (under progress). June 2000.

[PTS] Public Telegram Service. ITU-T Recommendation F1. XXXX

[RFC2459] R. Housley, W. Ford, W. Polk, D. Solo, "Internet X.509 Public
Key Infrastructure, Certificate and CRL Profile," RFC 2459, January
1999.

[PKCS9] RSA Laboratories, "The Public-Key Cryptography Standards
(PKCS)", RSA Data Security Inc., Redwood City, California, November
1993 Release.

[ISONR] ISO/IEC 10181-5:  Security Frameworks in Open Systems.
Non-Repudiation Framework. April 1997.

[ES201733] ETSI Standard ES 201 733 V1.1.3 (2000-05) Electronic
Signature Formats. Note: copies of ETSI ES 210 733 can be freely
downloaded from the ETSI web site www.etsi.org.

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8. Authors' Addresses

This Informational RFC has been produced in ETSI TC-SEC.

ETSI
F-06921 Sophia Antipolis, Cedex - FRANCE
650 Route des Lucioles - Sophia Antipolis
Valbonne - France
Tel: +33 4 92 94 42 00  Fax: +33 4 93 65 47 16
secretariat@etsi.fr
http://www.etsi.org

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Contact Point

Harri Rasilainen
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis, Cedex
FRANCE
harri.rasilainen@etsi.fr

Denis Pinkas
Bull S.A.
12, rue de Paris
B.P. 59
78231 Le Pecq
FRANCE
Denis.Pinkas @bull.net

John Ross
Security & Standards
192 Moulsham Street
Chelmsford, Essex
CM2 0LG
United Kingdom
ross@secstan.com

Nick Pope
Security & Standards
192 Moulsham Street
Chelmsford, Essex
CM2 0LG
United Kingdom
pope@secstan.com

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9. Full Copyright Statement

Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of developing
Internet standards in which case the procedures for copyrights defined
in the Internet Standards process must be followed, or as required to
translate it into languages other than English.

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The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Annex A (normative): ASN.1 Definitions

This annex provides a summary of all the ASN.1 syntax definitions for
new syntax defined in this document.

A.1  Definitions Using X.208 (1988) ASN.1 Syntax

NOTE:  The ASN.1 module defined in clause A.1 has precedence over that
defined in Annex A-2 in the case of any conflict.

    ETS-ElectronicSignatureFormats-88syntax { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0) 5}

DEFINITIONS EXPLICIT TAGS ::=

BEGIN

-- EXPORTS All -

IMPORTS

-- Crypographic Message Syntax (CMS): RFC 2630

  ContentInfo, ContentType, id-data, id-signedData, SignedData,
  EncapsulatedContentInfo, SignerInfo, id-contentType,
  id-messageDigest, MessageDigest, id-signingTime, SigningTime,
  id-countersignature, Countersignature

  FROM CryptographicMessageSyntax
    { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
      smime(16) modules(0) cms(1) }

-- ESS Defined attributes: RFC 2634
-- (Enhanced Security Services for S/MIME)

  id-aa-signingCertificate, SigningCertificate, IssuerSerial,
  id-aa-contentReference, ContentReference,
  id-aa-contentIdentifier, ContentIdentifier

  FROM ExtendedSecurityServices
     { iso(1) member-body(2) us(840) rsadsi(113549)
       pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) }

-- Internet X.509 Public Key Infrastructure
-- Certificate and CRL Profile: RFC 2459

  Certificate, AlgorithmIdentifier, CertificateList, Name,
  GeneralNames, GeneralName, DirectoryString,Attribute,
  AttributeTypeAndValue, AttributeType, AttributeValue,
  PolicyInformation, BMPString, UTF8String

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  FROM PKIX1Explicit88
  {iso(1) identified-organization(3) dod(6) internet(1)
   security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit-
   88(1)}

-- X.509 '97 Authentication Framework

AttributeCertificate

  FROM AuthenticationFramework
  {joint-iso-ccitt ds(5) module(1) authenticationFramework(7) 3}

-- The imported AttributeCertificate is defined using the X.680 1997
-- ASN.1 Syntax,
-- an equivalent using the 88 ASN.1 syntax may be used.

-- OCSP 2560

BasicOCSPResponse, ResponderID

  FROM OCSP {-- OID not assigned -- }

-- Time Stamp Protocol Internet Draft

TimeStampToken

  FROM PKIXTSP
  {iso(1) identified-organization(3) dod(6) internet(1)
  security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)}

-- S/MIME Object Identifier arcs used in this document
-- ===================================================

-- S/MIME  OID arc used in this document
-- id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
--             us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 16 }

-- S/MIME Arcs
-- id-mod  OBJECT IDENTIFIER ::= { id-smime 0 }
-- modules
-- id-ct   OBJECT IDENTIFIER ::= { id-smime 1 }
-- content types
-- id-aa   OBJECT IDENTIFIER ::= { id-smime 2 }
-- attributes
-- id-spq  OBJECT IDENTIFIER ::= { id-smime 5 }
-- signature policy qualifier
-- id-cti  OBJECT IDENTIFIER ::= { id-smime 6 }
-- commitment type identifier

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-- Definitions of Object Identifier arcs used in this document
-- ===========================================================

-- The allocation of OIDs to specific objects are given below with the
-- associated ASN.1 syntax definition

-- OID used referencing electronic signature mechanisms based on this
-- standard for use with the IDUP API (see annex D)

id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=
  { itu-t(0) identified-organization(4) etsi(0)
     electronic-signature-standard (1733) part1 (1)
         idupMechanism (4)etsiESv1(1) }

-- CMS Attributes Defined in this document
-- =======================================

-- Mandatory Electronic Signature Attributes

-- OtherSigningCertificate

    id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-aa(2) 19 }

OtherSigningCertificate ::=  SEQUENCE {
    certs        SEQUENCE OF OtherCertID,
    policies     SEQUENCE OF PolicyInformation OPTIONAL
                 -- NOT USED IN THIS DOCUMENT
}

OtherCertID ::= SEQUENCE {
     otherCertHash            OtherHash,
     issuerSerial             IssuerSerial OPTIONAL
}

OtherHash ::= CHOICE {
    sha1Hash     OtherHashValue,  -- This contains a SHA-1 hash
    otherHash    OtherHashAlgAndValue
}

OtherHashValue ::= OCTET STRING

OtherHashAlgAndValue ::= SEQUENCE {
  hashAlgorithm    AlgorithmIdentifier,
  hashValue        OtherHashValue
}

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-- Signature Policy Identifier

    id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-aa(2) 15 }

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SignaturePolicyIdentifier

"SignaturePolicy CHOICE {
         SignaturePolicyId          SignaturePolicyId,
         SignaturePolicyImplied     SignaturePolicyImplied
}

SignaturePolicyId ::= SEQUENCE {
        sigPolicyIdentifier   SigPolicyId,
        sigPolicyHash         SigPolicyHash,
        sigPolicyQualifiers   SEQUENCE SIZE (1..MAX) OF
                              SigPolicyQualifierInfo OPTIONAL
}

SignaturePolicyImplied ::= NULL

SigPolicyId ::= OBJECT IDENTIFIER

SigPolicyHash ::= ETSIHashAlgAndValue

SigPolicyQualifierInfo ::= SEQUENCE {
        sigPolicyQualifierId  SigPolicyQualifierId,
        sigQualifier          ANY DEFINED BY sigPolicyQualifierId
}

SigPolicyQualifierId ::=
        OBJECT IDENTIFIER

    id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-spq(5) 1 }

   SPuri ::= IA5String

    id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-spq(5) 2 }

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   SPUserNotice ::= SEQUENCE {
        noticeRef        NoticeReference   OPTIONAL,
        explicitText     DisplayText       OPTIONAL
}

   NoticeReference ::= SEQUENCE {
        organization     DisplayText,
        noticeNumbers    SEQUENCE OF INTEGER
}

   DisplayText ::= CHOICE {
        visibleString    VisibleString  (SIZE (1..200)),
        bmpString        BMPString      (SIZE (1..200)),
        utf8String       UTF8String     (SIZE (1..200))
}

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-- Optional Electronic Signature Attributes

-- Commitment Type

id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}

CommitmentTypeIndication ::= SEQUENCE {
  commitmentTypeId                 CommitmentTypeIdentifier,
  commitmentTypeQualifier          SEQUENCE SIZE (1..MAX) OF
                                   CommitmentTypeQualifier   OPTIONAL
}

CommitmentTypeIdentifier ::= OBJECT IDENTIFIER

CommitmentTypeQualifier ::= SEQUENCE {
    commitmentTypeIdentifier   CommitmentTypeIdentifier,
    qualifier                  ANY DEFINED BY commitmentTypeIdentifier
}

    id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    cti(6) 1}

    id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    cti(6) 2}

    id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1) member-
    body(2)  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    cti(6) 3}

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    id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
   cti(6) 4}

    id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    cti(6) 5}

    id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    cti(6) 6}

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-- Signer Location

   id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-
   body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
   id-aa(2) 17}

SignerLocation ::= SEQUENCE {
       -- at least one of the following must be present
      countryName      [0]  DirectoryString    OPTIONAL,
       -- as used to name a Country in X.500
      localityName     [1]  DirectoryString    OPTIONAL,
       -- as used to name a locality in X.500
      postalAdddress   [2]  PostalAddress      OPTIONAL
}

  PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString

-- Signer Attributes

    id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}

SignerAttribute ::= SEQUENCE OF CHOICE {
      claimedAttributes     [0] ClaimedAttributes,
      certifiedAttributes   [1] CertifiedAttributes
}

ClaimedAttributes ::= SEQUENCE OF Attribute

CertifiedAttributes ::= AttributeCertificate  -- as defined in X.509 :
see section 10.3

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-- Content Timestamp

    id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 20}

ContentTimestamp::= TimeStampToken

-- Validation Data

-- Signature Timestamp

    id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 14}

SignatureTimeStampToken ::= TimeStampToken

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-- Complete Certificate Refs.

id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}

CompleteCertificateRefs ::=  SEQUENCE OF OTHERCertID

-- Complete Revocation Refs

   id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-
   body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
   id-aa(2) 22}

CompleteRevocationRefs ::=  SEQUENCE OF CrlOcspRef

CrlOcspRef ::= SEQUENCE {
    crlids           [0] CRLListID      OPTIONAL,
    ocspids          [1] OcspListID     OPTIONAL,
    otherRev         [2] OtherRevRefs   OPTIONAL
}

CRLListID ::=  SEQUENCE {
    crls        SEQUENCE OF CrlValidatedID}

CrlValidatedID ::=  SEQUENCE {
     crlHash                   ETSIHash,
     crlIdentifier             CrlIdentifier OPTIONAL
}

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CrlIdentifier ::= SEQUENCE {
    crlissuer                 Name,
    crlIssuedTime             UTCTime,
    crlNumber                 INTEGER OPTIONAL
}

OcspListID ::=  SEQUENCE {
    ocspResponses        SEQUENCE OF OcspResponsesID}

OcspResponsesID ::=  SEQUENCE {
    ocspIdentifier              OcspIdentifier,
    ocspRepHash                 ETSIHash    OPTIONAL
}

OcspIdentifier ::= SEQUENCE {
  ocspResponderID    ResponderID,
                    -- as in OCSP response data
  producedAt      GeneralizedTime
                    -- as in OCSP response data
}

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OtherRevRefs ::= SEQUENCE {
   otherRevRefType         OtherRevRefType,
   otherRevRefs            ANY DEFINED BY otherRevRefType
}

OtherRevRefType ::= OBJECT IDENTIFIER

-- Certificate Values

id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}

CertificateValues ::=  SEQUENCE OF Certificate

-- Certificate Revocation Values

id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 24}

RevocationValues ::=  SEQUENCE {
   crlVals          [0] SEQUENCE OF CertificateList     OPTIONAL,
   ocspVals         [1] SEQUENCE OF BasicOCSPResponse   OPTIONAL,
   otherRevVals     [2] OtherRevVals
}

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OtherRevVals ::= SEQUENCE {
   otherRevValType  OtherRevValType,
  otherRevVals      ANY DEFINED BY otherRevValType
}

OtherRevValType ::= OBJECT IDENTIFIER

-- ES-C Timestamp

id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25}

ESCTimeStampToken ::= TimeStampToken

-- Time-Stamped Certificates and CRLs

id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 26}

TimestampedCertsCRLs ::= TimeStampToken

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-- Archive Timestamp

id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 27}

ArchiveTimeStampToken ::= TimeStampToken

END -- ETS-ElectronicSignatureFormats-88syntax --

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A.2  Definitions Using X.680 1997 ASN.1 Syntax

NOTE:  The ASN.1 module defined in clause A.1 has precedence over that
defined in clause A.2 in the case of any conflict.

    ETS-ElectronicSignatureFormats-97Syntax { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0) 6}

DEFINITIONS EXPLICIT TAGS ::=

BEGIN

-- EXPORTS All -

IMPORTS

-- Cryptographic Message Syntax (CMS): RFC 2630

  ContentInfo, ContentType, id-data, id-signedData, SignedData,
  EncapsulatedContentInfo, SignerInfo, id-contentType,
  id-messageDigest, MessageDigest, id-signingTime,
  SigningTime, id-countersignature, Countersignature

   FROM CryptographicMessageSyntax
    { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) modules(0) cms(1) }

-- ESS Defined attributes: RFC 2634 (Enhanced Security Services
-- for S/MIME)

   id-aa-signingCertificate, SigningCertificate, IssuerSerial,
   id-aa-contentReference, ContentReference,
   id-aa-contentIdentifier, ContentIdentifier

  FROM ExtendedSecurityServices
    { iso(1) member-body(2) us(840) rsadsi(113549)
       pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) }

-- Internet X.509 Public Key Infrastructure
- - Certificate and CRL Profile:RFC 2459

   Certificate, AlgorithmIdentifier, CertificateList, Name,
   GeneralNames, GeneralName, DirectoryString, Attribute,
   AttributeTypeAndValue, AttributeType, AttributeValue,
   PolicyInformation.

  FROM PKIX1Explicit93
    {iso(1) identified-organization(3) dod(6) internet(1)
     security(5) mechanisms(5) pkix(7) id-mod(0)
     id-pkix1-explicit-88(1)}

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-- X.509 '97 Authentication Framework

        AttributeCertificate

        FROM AuthenticationFramework
        {joint-iso-ccitt ds(5) module(1) authenticationFramework(7) 3}

-- OCSP 2560

      BasicOCSPResponse, ResponderID

  FROM OCSP

--  { OID not assigned }

-- Time Stamp Protocol Internet Draft TimeStampToken

  FROM PKIXTSP
  {iso(1) identified-organization(3) dod(6) internet(1)
   security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)}

-- S/MIME Object Identifier arcs used in this document
-- ===================================================

-- S/MIME  OID arc used in this document
-- id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
--             us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 16 }

-- S/MIME Arcs
-- id-mod  OBJECT IDENTIFIER ::= { id-smime 0 }
-- modules
-- id-ct   OBJECT IDENTIFIER ::= { id-smime 1 }
-- content types
-- id-aa   OBJECT IDENTIFIER ::= { id-smime 2 }
-- attributes
-- id-spq  OBJECT IDENTIFIER ::= { id-smime 5 }
-- signature policy qualifier
-- id-cti  OBJECT IDENTIFIER ::= { id-smime 6 }
-- commitment type identifier

-- Definitions of Object Identifier arcs used in this document
-- ===========================================================

-- The allocation of OIDs to specific objects are given below with the
-- associated ASN.1 syntax definition

-- OID used referencing electronic signature mechanisms based on this
-- standard for use with the IDUP API (see annex D)

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id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=
  { itu-t(0) identified-organization(4) etsi(0)
   electronic-signature-standard (1733) part1 (1)
   idupMechanism (4)etsiESv1(1) }

-- CMS Attributes Defined in this document
-- =======================================

-- Mandatory Electronic Signature Attributes
-- OtherSigningCertificate

id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-aa(2) 19 }

OtherSigningCertificate ::=  SEQUENCE {
    certs        SEQUENCE OF OtherCertID,
    policies     SEQUENCE OF PolicyInformation OPTIONAL
                 -- NOT USED IN THIS DOCUMENT
}

OtherCertID ::= SEQUENCE {
     otherCertHash            OtherHash,
     issuerSerial             IssuerSerial OPTIONAL
}

OtherHash ::= CHOICE {
    sha1Hash OtherHashValue,  -- This contains a SHA-1 hash
    otherHash OtherHashAlgAndValue
}

OtherHashValue ::= OCTET STRING

OtherHashAlgAndValue ::= SEQUENCE {
  hashAlgorithm  AlgorithmIdentifier,
  hashValue    OtherHashValue
}

-- Signature Policy Identifier

id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-aa(2) 15 }

SignaturePolicyIdentifier

"SignaturePolicy CHOICE {
         SignaturePolicyId          SignaturePolicyId,
         SignaturePolicyImplied     SignaturePolicyImplied
}

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SignaturePolicyId ::= SEQUENCE {
        sigPolicyIdentifier   SigPolicyId,
        sigPolicyHash         SigPolicyHash,
        sigPolicyQualifiers   SEQUENCE SIZE (1..MAX) OF
                                SigPolicyQualifierInfo OPTIONAL
}

SignaturePolicyImplied ::= NULL

SigPolicyId ::= OBJECT IDENTIFIER

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SigPolicyHash ::= ETSIHashAlgAndValue

SigPolicyQualifierInfo ::= SEQUENCE {
        sigPolicyQualifierId    SIG-POLICY-QUALIFIER.&id
                                 ({SupportedSigPolicyQualifiers}),
        qualifier               SIG-POLICY-QUALIFIER.&Qualifier
                                ({SupportedSigPolicyQualifiers}
                                 {@sigPolicyQualifierId})OPTIONAL }

SupportedSigPolicyQualifiers SIG-POLICY-QUALIFIER ::=
                           { noticeToUser | pointerToSigPolSpec }

SIG-POLICY-QUALIFIER ::= CLASS {
        &id             OBJECT IDENTIFIER UNIQUE,
        &Qualifier      OPTIONAL }

WITH SYNTAX {
        SIG-POLICY-QUALIFIER-ID     &id
        [SIG-QUALIFIER-TYPE &Qualifier] }

noticeToUser SIG-POLICY-QUALIFIER ::= {
      SIG-POLICY-QUALIFIER-ID id-sqt-unotice SIG-QUALIFIER-TYPE
                                            SPUserNotice
                                                        }

pointerToSigPolSpec SIG-POLICY-QUALIFIER ::= {
      SIG-POLICY-QUALIFIER-ID id-sqt-uri SIG-QUALIFIER-TYPE SPuri }

    id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-spq(5) 1 }

   SPuri ::= IA5String

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  id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-spq(5) 2 }

   SPUserNotice ::= SEQUENCE {
        noticeRef        NoticeReference OPTIONAL,
        explicitText     DisplayText OPTIONAL
}

   NoticeReference ::= SEQUENCE {
        organization     DisplayText,
        noticeNumbers    SEQUENCE OF INTEGER
}

   DisplayText ::= CHOICE {
        visibleString    VisibleString  (SIZE (1..200)),
        bmpString        BMPString      (SIZE (1..200)),
        utf8String       UTF8String     (SIZE (1..200))
}

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-- Optional Electronic Signature Attributes

-- Commitment Type

id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}

CommitmentTypeIndication ::= SEQUENCE {
  commitmentTypeId CommitmentTypeIdentifier,
  commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
                                           CommitmentTypeQualifier
                                           OPTIONAL}

CommitmentTypeIdentifier ::= OBJECT IDENTIFIER

CommitmentTypeQualifier ::= SEQUENCE {
        commitmentQualifierId       COMMITMENT-QUALIFIER.&id,
        qualifier                   COMMITMENT-QUALIFIER.&Qualifier
                                                  OPTIONAL }

COMMITMENT-QUALIFIER ::= CLASS {
                    &id             OBJECT IDENTIFIER UNIQUE,
                    &Qualifier      OPTIONAL }
WITH SYNTAX {
         COMMITMENT-QUALIFIER-ID     &id
                        [COMMITMENT-TYPE &Qualifier] }

  id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1)
      member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
      smime(16) cti(6) 1}

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  id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1)
      member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
      smime(16) cti(6) 2}

  id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1)
      member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
      smime(16) cti(6) 3}

  id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1)
      member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
      smime(16) cti(6) 4}

  id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1)
      member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
      smime(16) cti(6) 5}

  id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1)
      member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
      smime(16) cti(6) 6}

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-- Signer Location

id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}

SignerLocation ::= SEQUENCE {
                       -- at least one of the following must be present
      countryName [0] DirectoryString OPTIONAL,
        -- As used to name a Country in X.500
      localityName [1] DirectoryString OPTIONAL,
         -- As used to name a locality in X.500
      postalAdddress [2] PostalAddress OPTIONAL }

  PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString

-- Signer Attributes

id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}

SignerAttribute ::= SEQUENCE OF CHOICE {
      claimedAttributes  [0] ClaimedAttributes,
      certifiedAttributes [1] CertifiedAttributes }

ClaimedAttributes ::= SEQUENCE OF Attribute

CertifiedAttributes ::= AttributeCertificate
-- As defined in X.509 : see section 10.3

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-- Content Timestamp

id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1)
      member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
      smime(16) id-aa(2) 20}

ContentTimestamp::= TimeStampToken

-- Validation Data

-- Signature Timestamp

id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1)
     member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
     smime(16) id-aa(2) 14}

SignatureTimeStampToken ::= TimeStampToken

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-- Complete Certificate Refs.

id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}

CompleteCertificateRefs ::=  SEQUENCE OF OTHERCertID

-- Complete Revocation Refs

id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}

CompleteRevocationRefs ::=  SEQUENCE OF CrlOcspRef

CrlOcspRef ::= SEQUENCE {
    crlids           [0] CRLListID   OPTIONAL,
    ocspids          [1] OcspListID  OPTIONAL,
  otherRev     [2] OtherRevRefs OPTIONAL
                                          }

CRLListID ::=  SEQUENCE {
    crls        SEQUENCE OF CrlValidatedID}

CrlValidatedID ::=  SEQUENCE {
     crlHash                   ETSIHash,
     crlIdentifier             CrlIdentifier OPTIONAL}

CrlIdentifier ::= SEQUENCE {
    crlissuer                 Name,
    crlIssuedTime             UTCTime,
    crlNumber                 INTEGER OPTIONAL
                                            }

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OcspListID ::=  SEQUENCE {
    ocspResponses        SEQUENCE OF OcspResponsesID}

OcspResponsesID ::=  SEQUENCE {
    ocspIdentifier              OcspIdentifier,
    ocspRepHash                 ETSIHash    OPTIONAL
                                            }

OcspIdentifier ::= SEQUENCE {
  ocspResponderID    ResponderID,
                        -- As in OCSP response data
  producedAt      GeneralizedTime
                        -- As in OCSP response data
                                             }

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OtherRevRefs ::= SEQUENCE {
   otherRevRefType  OTHER-REVOCATION-REF.&id,
  otherRevRefs  OTHER-REVOCATION-REF.&Type
                                              }

OTHER-REVOCATION-REF ::= CLASS {
    &Type,
    &id  OBJECT IDENTIFIER UNIQUE }
  WITH SYNTAX {
    &Type ID &id }

-- Certificate Values

id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}

CertificateValues ::=  SEQUENCE OF Certificate

-- Certificate Revocation Values

id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1)
     member-body(2)us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
     smime(16) id-aa(2) 24}

RevocationValues ::=  SEQUENCE {
   crlVals          [0] SEQUENCE OF CertificateList OPTIONAL,
   ocspVals         [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
   otherRevVals      [2] OtherRevVals }

OtherRevVals ::= SEQUENCE {
   otherRevValType  OTHER-REVOCATION-VAL.&id,
  otherRevVals  OTHER-REVOCATION-VAL.&Type
                                               }

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OTHER-REVOCATION-VAL ::= CLASS {
    &Type,
    &id  OBJECT IDENTIFIER UNIQUE }
  WITH SYNTAX {
    &Type ID &id }

-- ES-C Timestamp

id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1)
     member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
     smime(16) id-aa(2) 25}

ESCTimeStampToken ::= TimeStampToken

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-- Time-Stamped Certificates and CRLs

id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) id-aa(2) 26}

TimestampedCertsCRLs ::= TimeStampToken

-- Archive Timestamp

id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1)
   member-body(2)us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
   smime(16) id-aa(2) 27}

ArchiveTimeStampToken ::= TimeStampToken

END                -- ETS-ElectronicSignatureFormats-97Syntax

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Annex B (informative): General Description

This annex captures the concepts that apply to this document and the
rational for the elements of the specification defined using ASN.1 in
the main text of this document.

The specification below includes a description why the component is
needed, with a brief description of the vulnerabilities and threats
and the manner by which they are countered.

B.1  The Signature Policy

The signature policy is a set of rules for the creation and validation
of an electronic signature, under which the signature can be
determined to be valid. A given legal/contractual context may
recognize a particular signature policy as meeting its requirements.
A signature policy may be issued, for example, by a party relying on
the electronic signatures and selected by the signer for use with that
relying party. Alternatively, a signature policy may be established
through an electronic trading association for use amongst its members.
Both the signer and verifier use the same signature policy.

A

The signature policy may be explicitly identified or may be implied by
the semantics of the data being signed and other external data like a
contract being referenced which itself refers to a signature policy.

An explicit signature policy has a globally unique reference, which is
bound to an electronic signature by the signer as part of the signature
calculation.

The signature policy needs to be available in human readable form so
that it can be assessed to meet the requirements of the legal and
contractual context in which it is being applied. To facilitate the
automatic processing of an electronic signature the parts of the
signature policy which specify the electronic rules for the creation
and validation of the electronic signature also needs to be in a
computer processable form.

The signature policy thus includes the following:

     * Information about the signature policy that can be displayed
       to the signer or the verifiers.
     * Rules, which apply to functionality, covered by this document
       (referred to as the Signature Validation Policy).
     * Rules which may be implied through adoption of Certificate
       Policies that apply to the electronic signature (e.g. rules for
       ensuring the secrecy of the private signing key).
     * Rules, which relate to the environment used by the signer,
       e.g. the use of an agreed CAD (Card Accepting Device) used
       in conjunction with a smart card.

The

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An explicit Signature Validation Policy may be structured so that it
can be computer processable. Any format of the signature validation
policy is allowed by this document. However, for a given explicit
signature policy there must be one definitive form that has a unique
binary encoded value.

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The Signature Validation Policy includes rules regarding use of TSPs
(CA, Attribute Authorities, Time Stamping Authorities) as well as
rules defining the components of the electronic signature that must be
provided by the signer with data required by the verifier to provide
long term proof.

B.2  Signed Information

The information being signed may be defined as a MIME-encapsulated
message which can be used to signal the format of the content in order
to select the right display or application. It can be composed of
formatted text (e.g. EDIFACT), free text or of fields from an
electronic form (e-form). For example, the Adobe(tm) format "pdf" may
be used or the eXtensible Mark up Language (XML).

B.3  Components of an Electronic Signature

B.3.1  Reference to the Signature Policy

The definition of electronic signature includes: "a commitment has
been explicitly endorsed under a "Signature policy", at a given time,
by a signer under an identifier, e.g. a name or a pseudonym, and
optionally a role".

When two independent parties want to evaluate an electronic signature,
it is fundamental that they get the same result. To meet this
requirement the technical components and technical aspects used in
creating the same signature policy must be referenced, this is provided used by a
reference to the "Signature Validation Policy". signer and
verifier.

The "Signature
Validation Policy" defines:

    * the components of an electronic signature to policy may be provided explicitly identified or may be implied by
the
      signer;

    * any additional components (i.e. verifier components) used to
      validate an electronic signature at the time semantics of receipt by a
      verifier the data being signed and later by an arbitrator, auditor or other
      independent parties. external data which
designate the signature policy to be used.

By signing over the signature policy identifier, the algorithm identifier and the hash of the signature policy, the signer explicitly
indicates that he or she has applied the signature policy in creating
the signature. Thus, undertakes any commitments explicit or implied by commitments.

In order to unambiguously identify an explicit signature policy that is
to be used to verify the signature policy, any indication an identifier and hash of commitment type included in the
electronic signature, and
"Signature policy" shall be part of the user data that signed data. Additional
information about the explicit policy (e.g. web reference to the
document) may be carried as "qualifiers" to the signature policy
identifier.

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When the signature policy not explicitly identified, but is signed.

The hash algorithm implied by
the semantics of the data being signed, then the signature will include
a signature policy identifier and value is included to ensure that
both indicates that the signer and verifier use exactly signature policy
is implied. In this case the verification rules must be determined by
using other external data which will designate the same signature policy.
This unambiguously binds policy to
be used. If it may be determined from the signer and verifier context that all the
documents to be verified refer to same definitive
form of the same signature policy, then that
policy has a unique binary encoding.

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In order to identify unambiguously the "Signature Validation Policy"
to be used to verify the signature an identifier and hash of the
"Signature policy" must be part of the signed data. Additional
information about the policy (e.g. web reference to the document) may
be carried as "qualifiers" to the signature policy identifier.

B.3.2  Commitment Type Indication

The definition of electronic signature includes: "a commitment has
been explicitly endorsed under a signature policy, at a given time,
by a signer under an identifier, e.g. a name or a pseudonym, and
optionally a role".

The commitment type can be indicated in the electronic signature
either:

      * explicitly using a "commitment type indication" in the
        electronic signature;

      * implicitly or explicitly from the semantics of the signed data.

If the indicated commitment type is explicit using a "commitment type
indication" in the electronic signature, acceptance of a verified
signature implies acceptance of the semantics of that commitment type.
The semantics of explicit commitment types indications must be
specified either as part of the signature policy or may be registered
for generic use across multiple policies.

If a signature includes a commitment type indication other than one of
those recognized under the signature policy the signature must be
treated as invalid.

How commitment is indicated using the semantics of the data being
signed is outside the scope of this document.

NOTE:  Examples of commitment indicated through the semantics of the
data being signed, are:

     * An explicit commitment made by the signer indicated by the type
       of data being signed over. Thus, the data structure being
       signed can have an explicit commitment within the context of
       the application (e.g. EDIFACT purchase order).

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     * An implicit commitment which is a commitment made by the signer
       because the data being signed over has specific semantics
       (meaning) which is only interpretable by humans, (i.e. free
       text).

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B.3.3  Certificate Identifier from the Signer

The definition of the ETSI electronic signature includes: "a
commitment has been explicitly endorsed under a signature policy,
at a given time, by a signer under an identifier, e.g. a name or a
pseudonym, and optionally a role."

In many real life environments users will be able to get from
different CAs or even from the same CA, different certificates
containing the same public key for different names. The prime
advantage is that a user can use the same private key for different
purposes. Multiple use of the private key is an advantage when a smart
card is used to protect the private key, since the storage of a smart
card is always limited. When several CAs are involved, each different
certificate may contain a different identity, e.g. as a national or as
an employee from a company. Thus when a private key is used for
various purposes, the certificate is needed to clarify the context in
which the private key was used when generating the signature. Where
there is the possibility of multiple use of private keys it is
necessary for the signer to indicate to the verifier the precise
certificate to be used.

Many current schemes simply add the certificate after the signed data
and thus are subject to various substitution attacks. An example of a
substitution attack is a "bad" CA that would issue a certificate to
someone with the public key of someone else. If the certificate from
the signer was simply appended to the signature and thus not protected
by the signature, any one could substitute one certificate by another
and the message would appear to be signed by some one else.

In order to counter this kind of attack, the identifier of the signer
has to be protected by the digital signature from the signer.

Although it does not provide the same advantages as the previous
technique, another technique to counter that threat has been
identified. It requires all CAs to perform a Proof Of Possession of
the private key at the time of registration. The problem with that
technique is that it does not provide any guarantee at the time of
verification and only some proof "after the event" may be obtained, if
and only if the CA keeps the Proof Of Possession in audit trail.

In order to identify unambiguously the certificate to be used for the
verification of the signature an identifier of the certificate from
the signer must be part of the signed data.

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B.3.4  Role Attributes

The definition of electronic signature includes: "a commitment has
been explicitly endorsed under a non repudiation security policy,
at a given time, by a signer under an identifier, e.g. a name or a
pseudonym, and optionally a role. "

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While the name of the signer is important, the position of the signer
within a company or an organization can be even more important. Some
contracts may only be valid if signed by a user in a particular role,
e.g. a Sales Director. In many cases whom the sales Director really
is, is not that important but being sure that the signer is empowered
by his company to be the Sales Director is fundamental.

This document defines two different ways for providing this feature:

      * by placing a claimed role name in the CMS signed
        attributes field;

     * by placing a attribute certificate containing a certified
       role name in the CMS signed attributes field.

NOTE:  Another possible approach would have been to use additional
attributes containing the roles name(s) in the signer's certificate.
However, it was decided not to follow this approach as it breaks the
basic philosophy of the certificate being issued for one primary
purpose. Also, by using separate certificates for management of the
signer's identity certificate and management of additional roles can
simplify the management, as new identity keys need not be issued if a
use of role is to be changed.

B.3.5.1  Claimed Role

The signer may be trusted to state his own role without any
certificate to corroborate this claim. In which case the claimed role
can be added to the signature as a signed attribute.

B.3.5.2  Certified Role

Unlike public key certificates that bind an identifier to a public
key, Attribute Certificates bind the identifier of a certificate to
some attributes, like a role. An Attribute Certificate is NOT issued
by a CA but by an Attribute Authority (AA). The Attribute Authority
will be most of the time under the control of an organization or a
company that is best placed to know which attributes are relevant for
which individual.

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The Attribute Authority may use or point to public key certificates
issued by any CA, provided that the appropriate trust may be placed
in that CA. Attribute Certificates may have various periods of
validity. That period may be quite short, e.g. one day. While this
requires that a new Attribute Certificate is obtained every day, valid
for that day, this can be advantageous since revocation of such
certificates may not be needed. When signing, the signer will have to
specify which Attribute Certificate it selects. In order to do
so, a reference to the Attribute Certificate will have to be included
in the signed data in order to be protected by the digital signature
from the signer.

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In order to identify unambiguously the attribute certificate(s) to be
used for the verification of the signature an identifier of the
attribute certificate(s) from the signer must be part of the signed
data.

B.3.5  Signer Location

In some transactions the purported location of the signer at the time
he or she applies his signature may need to be indicated. For this
reason an optional location indicator must be able to be included.

In order to provide indication of the location of the signer at the
time he or she applied his signature a  location attribute may be
included in the signature.

B.3.6  Signing Time

The definition of electronic signature includes: "a commitment has
been explicitly endorsed under a signature policy, at a given time,
by a signer under an identifier, e.g. a name or a pseudonym, and
optionally a
role. "

There are several ways to address this problem. The solution adopted
in this document is to sign over a time which the signer claims is the
signing time (i.e. claimed signing time) and to require a trusted
time stamp to be obtained when building a ES with Timestamp. When a
verifier accepts a signature, the two times must be within acceptable
limits.

The solution that is adopted in this document offers the major
advantage that electronic signatures can be generated without any on-
line connection to a trusted time source (i.e. they may be generated
off-line).

Thus two dates and two signatures are required:

     * a signing time indicated by the signer and which is part of
       the data signed by the signer (i.e. part of the basic
       electronic signature);

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     * a time indicated by a TimeStamping Authority (TSA) which is
       signed over the digital signature value of the basic electronic
       signature. The signer, verifier or both may obtain the TSA
       timestamp.

In order for an electronic signature to be valid under a signature
policy, it must be timestamped by a TSA where the signing time as
indicated by the signer and the time of time stamping as indicated by
a TSA must be "close enough" to meet the requirements of the signature
validation policy.

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"Close enough" means a few minutes, hours or even days according to
the "Signature Validation Policy".

NOTE:  The need for Timestamping is further explained in clause B.4.5.
A further optional attribute is defined in this document to timestamp
the content, to provide proof of the existence of the content, at the
time indicated by the timestamp.

Using this optional attribute a trusted secure time may be obtained
before the document is signed and included under the digital signature.
This solution requires an on-line connection to a trusted timestamping
service before generating the signature and may not represent the
precise signing time, since it can be obtained in advance.  However,
this optional attribute may be used by the signer to prove that the
signed object existed before the date included in the timestamp (see
3.12.3, Content Timestamp).

Also, the signing time should be between the time indicated by this
timestamp and time indicated by the ES-T timestamp.

B.3.7  Content Format

When presenting signed data to a human user it may be important that
there is no ambiguity as to the presentation of the signed information
to the relying party. In order for the appropriate representation
(text, sound or video) to be selected by the relying party a content
hint may be indicated by the signer. If a relying party system does not
use the format specified in the content hints to present the data to
the relying party, the electronic signature may not be valid.

B.4  Components of Validation Data

B.4.1  Revocation Status Information

A verifier will have to prove that the certificate of the signer was
valid at the time of the signature. This can be done by either:

     * using Certificate Revocation Lists (CRLs);

     * using responses from an on-line certificate status server
       (for example; obtained through the OCSP protocol).

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B.4.2  CRL Information

When using CRLs to get revocation information, a verifier will have to
make sure that he or she gets at the time of the first verification the
appropriate certificate revocation information from the signer's CA.
This should be done as soon as possible to minimize the time delay
between the generation and verification of the signature. This involves
checking that the signer certificate serial number is not included in
the CRL. The signer, the verifier or any other third party may obtain
either this CRL. If obtained by the signer, then it must be conveyed
to the verifier. It may be convenient to archive the CRL for ease of
subsequent verification or arbitration.

Alternatively, provided the CRL is archived elsewhere which is
accessible for the purpose of arbitration, then the serial number of
the CRL used may be archived together with the verified electronic
signature.

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It may happen that the certificate serial number appears in the CRL
but with the status "suspended" (i.e. on hold). In such a case, the
electronic signature is not yet valid, since it is not possible to
know whether the certificate will or will not be revoked at the end
of the suspension period. If a decision has to be taken immediately
then the signature has to be considered as invalid. If a decision can
wait until the end of the suspension period, then two cases are
possible:

     * the certificate serial number has disappeared from the list
       and thus the certificate can be considered as valid and that
       CRL must be captured and archived either by the verifier or
       elsewhere and be kept accessible for the purpose of arbitration.

     * the certificate serial number has been maintained on the list
       with the status definitively revoked and thus the electronic
       signature must be considered as invalid and discarded.

At this point the verifier may be convinced that he or she got a valid
signature, but is not yet in a position to prove at a later time that
the signature was verified as valid. Before addressing this point, an
alternative to CRL is to use OCSP responses.

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B.4.3  OCSP Information

When using OCSP to get revocation information , a verifier will have
to make sure that he or she gets at the time of the first verification
an OCSP response that contains the status "valid". This should be done
as soon as possible after the generation of the signature. The signer,
the verifier or any other third party may fetch this OCSP response.
Since OSCP responses are transient and thus are not archived by any
TSP including CA, it is the responsibility of every verifier to make
sure that it is stored in a safe place. The simplest way is to store
them associated with the electronic signature. An alternative would be
to store them in some storage so that they can then be easily
retrieved.

In the same way as for the case of the CRL, it may happen that the
certificate is declared as invalid but with the secondary status
"suspended".

In such a case, the electronic signature is not yet valid, since it is
not possible to know whether the certificate will or will not be
revoked at the end of the suspension period. If a decision has to be
taken immediately then the electronic signature has to be considered
as invalid. If a decision can wait until the end of the suspension
period, then two cases are possible:

     * An OCSP response with a valid status is obtained at a later
       date and thus the certificate can be considered as valid and
       that OCSP response must be captured.

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     * An OCSP response with an invalid status is obtained with a
       secondary status indicating that the certificate is
       definitively revoked and thus the electronic signature must be
       considered as invalid and discarded.

As in the CRL case, at this point, the verifier may be convinced that
he or she got a valid signature, but is not yet in a position to prove
at a later time that the signature was verified as valid.

B.4.4  Certification Path

A verifier will have to prove that the certification path was valid,
at the time of the signature, up to a trust point according to the
naming constraints and the certificate policy constraints from the
"Signature Validation Policy". It will be necessary to capture all the
certificates from the certification path, starting with those from the
signer and ending up with those of the self-signed certificate from
one trusted root of the "Signature Validation Policy". In addition, it
will be necessary to capture the Authority Revocation Lists (ARLs) to
prove than none of the CAs from the chain was revoked at the time of
the signature.

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As in the OCSP case, at this point, the verifier may be convinced that
he or she got a valid signature, but is not yet in a position to prove
at a later time that the signature was verified as valid.

B.4.5  Timestamping for Long Life of Signature

An important property for long standing signatures is that a
signature, having been found once to be valid, must continue to be so
months or years later.

A signer, verifier or both may be required to provide on request,
proof that a digital signature was created or verified during the
validity period of the all the certificates that make up the
certificate path. In this case, the signer, verifier or both will
also be required to provide proof that all the user and CA
certificates used were not revoked when the signature was created
or verified.

It would be quite unacceptable, to consider a signature as invalid
even if the keys or certificates were later compromised. Thus there
is a need to be able to demonstrate that the signature keys was valid
around the time that the signature was created to provide long term
evidence of the validity of a signature.

It could be the case that a certificate was valid at the time of the
signature but revoked some time later. In this event, evidence must be
provided that the document was signed before the signing key was
revoked.

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Timestamping by a Time Stamping Authority (TSA) can provide such
evidence. A time stamp is obtained by sending the hash value of the
given data to the TSA. The returned "timestamp" is a signed document
that contains the hash value, the identity of the TSA, and the time of
stamping. This proves that the given data existed before the time of
stamping. Timestamping a digital signature (by sending a hash of the
signature to the TSA) before the revocation of the signer's private
key, provides evidence that the signature has been created before the
key was revoked.

If a recipient wants to hold a valid electronic signature he will have
to ensure that he has obtained a valid time stamp for it, before that
key (and any key involved in the validation) is revoked. The sooner
the timestamp is obtained after the signing time, the better.

It is important to note that signatures may be generated "off-line"
and time-stamped at a later time by anyone, for example by the signer
or any recipient interested in the value of the signature. The time
stamp can thus be provided by the signer together with the signed
document, or obtained by the recipient following receipt of the signed
document.

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The time stamp is NOT a component of the Electronic Signature, but the
essential component of the ES with Timestamp.

It is required in this document that signer's digital signature value
is timestamped by a trusted source, known as a TimeStamping Authority.

This document requires that the signer's digital signature value is
timestamped by a trusted source before the electronic signature can
become a ES with Complete validation data (ES-C). The acceptable TSAs
are specified in the Signature Validation Policy.

Should both the signer and verifier be required to timestamp the
signature value to meet the requirements of the signature policy, the
signature policy MAY specify a permitted time delay between the two
time stamps.

B.4.6  Timestamping before CA Key Compromises

Timestamped extended electronic signatures are needed when there is a
requirement to safeguard against the possibility of a CA key in the
certificate chain ever being compromised. A verifier may be required
to provide on request, proof that the certification path and the
revocation information used a the time of the signature were valid,
even in the case where one of the issuing keys or OCSP responder keys
is later compromised.

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The current document defines two ways of using timestamps to protect
against this compromise:

    * Timestamp the ES with Complete validation data, when an OCSP
      response is used to get the status of the certificate from the
      signer.

    * Timestamp only the certification path and revocation information
      references when a CRL is used to get the status of the
      certificate from the signer.

NOTE:  the signer, verifier or both may obtain the timestamp.

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B.4.6.1  Timestamping the ES with Complete validation data

When an OCSP response is used, it is necessary to time stamp in
particular that response in the case the key from the responder would
be compromised. Since the information contained in the OCSP response
is user specific and time specific, an individual time stamp is needed
for every signature received. Instead of placing the time stamp only
over the certification path references and the revocation information
references, which include the OCSP response, the time stamp is placed
on the ES-C. Since the certification path and revocation information
references are included in the ES with Complete validation data they
are also protected. For the same cryptographic price, this provides an
integrity mechanism over the ES with Complete validation data. Any
modification can be immediately detected. It should be noticed that
other means of protecting/detecting the integrity of the ES with
Complete Validation Data exist and could be used.

Although the technique requires a time stamp for every signature, it
is well suited for individual users wishing to have an integrity
protected copy of all the validated signatures they have received.

By timestamping the complete electronic signature, including the
digital signature as well as the references to the certificates and
revocation status information used to support validation of that
signature, the timestamp ensures that there is no ambiguity in the
means of validating that signature.

This technique is referred to as ES with eXtended validation data
(ES-X), type 1 Timestamped in this document.

NOTE:  Trust is achieved in the references by including a hash of the
data being referenced.

If it is desired for any reason to keep a copy of the additional data
being referenced, the additional data may be attached to the
electronic signature, in which case the electronic signature becomes
a ES-X Long as defined by this document.

A ES-X Long Timestamped  is simply the concatenation of a ES-X
Timestamped  with a copy of the additional data being referenced.

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B.4.6.2  Timestamping Certificates and Revocation Information

References Timestamping each ES with Complete validation data as
defined above may not be efficient, particularly when the same set of
CA certificates and CRL information is used to validate many
signatures.

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Timestamping CA certificates will stop any attacker from issuing bogus
CA certificates that could be claimed to existing before the CA key
was compromised. Any bogus timestamped CA certificates will show that
the certificate was created after the legitimate CA key was
compromised. In the same way, timestamping CA CRLs, will stop any
attacker from issuing bogus CA CRLs which could be claimed to existing
before the CA key was compromised.

Timestamping of commonly used certificates and CRLs can be done
centrally, e.g. inside a company or by a service provider. This method
reduces the amount of data the verifier has to timestamp, for example
it could reduce to just one time stamp per day (i.e. in the case were
all the signers use the same CA and the CRL applies for the whole day).
The information that needs to be time stamped is not the actual
certificates and CRLs but the unambiguous references to those
certificates and CRLs.

To comply with extended validation data, type 2 Timestamped, this
document requires the following:

     * All the CA certificates references and revocation information
       references (i.e. CRLs) used in validating the ES-C are covered
       by one or more timestamp.

Thus a ES-C with a timestamp signature value at time T1, can be proved
valid if all the CA and CRL references are timestamped at time T1+.

B.4.7  Timestamping for Long Life of Signature

Advances in computing increase the probability of being able to break
algorithms and compromise keys. There is therefore a requirement to be
able to protect electronic signatures against this probability.

Over a period of time weaknesses may occur in the cryptographic
algorithms used to create an electronic signature (e.g. due to the
time available for cryptoanalysis, or improvements in cryptoanalytical
techniques). Before this such weaknesses become likely, a verifier
should take extra measures to maintain the validity of the electronic
signature. Several techniques could be used to achieve this goal
depending on the nature of the weakened cryptography. In order to
simplify, a single technique, called Archive validation data, covering
all the cases is being used in this document.

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Archive validation data consists of the Complete validation data and
the complete certificate and revocation data, time stamped together
with the electronic signature. The Archive validation data is
necessary if the hash function and the crypto algorithms that were
used to create the signature are no longer secure. Also, if it cannot
be assumed that the hash function used by the Time Stamping Authority
is secure, then nested timestamps of Archived Electronic Signature are
required.

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The potential for Trusted Service Provider (TSP) key compromise should
be significantly lower than user keys, because TSP(s) are expected to
use stronger cryptography and better key protection. It can be expected
that new algorithms (or old ones with greater key lengths) will be
used. In such a case, a sequence of timestamps will protect against
forgery. Each timestamp needs to be affixed before either the
compromise of the signing key or of the cracking of the algorithms used
by the TSA. TSAs (TimeStamping Authorities) should have long keys (e.g.
which at the time of drafting this document was 2048 bits for the
signing RSA algorithm) and/or a "good" or different algorithm.

Nested timestamps will also protect the verifier against key compromise
or cracking the algorithm on the old electronic signatures.

The process will need to be performed and iterated before the
cryptographic algorithms used for generating the previous time stamp
are no longer secure. Archive validation data may thus bear multiple
embedded time stamps.

B.4.8  Reference to Additional Data

Using type 1 or 2 of Timestamped extended validation data verifiers
still needs to keep track of all the components that were used to
validate the signature, in order to be able to retrieve them again
later on. These components may be archived by an external source like
a trusted service provider, in which case referenced information that
is provided as part of the ES with Complete validation data (ES-C) is
adequate. The actual certificates and CRL information reference in the
ES-C can be gathered when needed for arbitration.

B.4.9  Timestamping for Mutual Recognition

In some business scenarios both the signer and the verifier need to
timestamp their own copy of the signature value. Ideally the two
timestamps should be as close as possible to each other.

Example: A contract is signed by two parties A and B representing
their respective organizations, to timestamp the signer and verifier
data two approaches are possible:

      * under the terms of the contract pre-defined common "trusted"
        TSA may be used;

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      * if both organizations run their own timestamping services, A
        and B can have the transaction timestamped by these two
        timestamping services. In the latter case, the electronic
        signature will only be considered as valid, if both timestamps
        were obtained in due time (i.e. there should not be a long
        delay between obtaining the two timestamps). Thus, neither A
        nor B can repudiate the signing time indicated by their own
        timestamping service.

Therefore, A and B do not need to agree on a common "trusted" TSA to
get a valid transaction.

It is important to note that signatures may be generated "off-line"
and timestamped at a later time by anyone, e.g. by the signer or any
recipient interested in validating the signature. The timestamp over
the signature from the signer can thus be provided by the signer
together with the signed document, and /or obtained by the verifier
following receipt of the signed document.

The business scenarios may thus dictate that one or more of the long-
term signature timestamping methods describe above be used. This will
need to be part of a mutually agreed the Signature Validation Policy
with is part of the overall signature policy under which digital
signature may be used to support the business relationship between the
two parties.

B.4.10  TSA Key Compromise

TSA servers should be built in such a way that once the private
signature key is installed, that there is minimal likelihood of
compromise over as long as possible period. Thus the validity period
for the TSA's keys should be as long as possible.

Both the ES-T and the ES-C contain at least one time stamp over the
signer's signature. In order to protect against the compromise of the
private signature key used to produce that timestamp, the Archive
validation data can be used when a different TimeStamping Authority key
is involved to produce the additional timestamp. If it is believed that
the TSA key used in providing an earlier timestamp may ever be
compromised (e.g. outside its validity period), then the ES-A should be
used. For extremely long periods this may be applied repeatedly using
new TSA keys.

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B.5  Multiple Signatures

Some electronic signatures may only be valid if they bear more than one
signature. This is the case generally when a contract is signed between
two parties. The ordering of the signatures may or may not be
important, i.e. one may or may not need to be applied before the other.

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Several forms of multiple and counter signatures may need to be
supported, which fall into two basic categories:

     * independent signatures;
     * embedded signatures.

Independent signatures are parallel signatures where the ordering of
the signatures is not important. The capability to have more than one
independent signature over the same data must be provided.

Embedded signatures are applied one after the other and are used where
the order the signatures are applied is important. The capability to
sign over signed data must be provided.

These forms are described in clause 3.13. All other multiple signature
schemes, e.g. a signed document with a countersignature, double
countersignatures or multiple signatures, can be reduced to one or more
occurrence of the above two cases.

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Annex C (informative):  Identifiers and roles

C.1  Signer Name Forms

The name used by the signer, held as the subject in the signer's
certificate, must uniquely identify the entity.  The name must be
allocated and verified on registration with the Certification
Authority, either directly or indirectly through a Registration
Authority, before being issued with a Certificate.

This document places no restrictions on the form of the name. The
subject's name may be a distinguished name, as defined in [RFC2459],
held in the subject field of the certificate, or any other name form
held in the X.509 subjectAltName certificate extension field. In the
case that the subject has no distinguished name, the subject name can
be an empty sequence and the subjectAltName extension must be critical.

C.2  TSP Name Forms

All TSP name forms (Certification Authorities, Attribute Authorities
and TimeStamping Authorities) must be in the form of a distinguished
name held in the subject field of the certificate.

The TSP name form must include the legal jurisdiction (i.e. country)
under which it operates and an identification for the organization
providing the service.

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C.3  Roles and Signer Attributes

Where a signer signs as an individual but wishes to also identify
him/herself as acting on behalf of an organization, it may be necessary
to provide two independent forms of identification. The first identity,
with is directly associated with the signing key identifies him/her as
an individual. The second, which is managed independently, identifies
that person acting as part of the organization, possibly with a given
role.

In this case the first identity is carried in the
subject/subjectAltName field of the signer's certificate as described
above.

This document supports the following means of providing a second form
of identification:

     * by placing a secondary name field containing a claimed role in
       the CMS signed attributes field;

     * by placing an attribute certificate containing a certified role
       in the CMS signed attributes field.