draft-ietf-smime-3851bis-03.txt   draft-ietf-smime-3851bis-04.txt 
S/MIME WG Blake Ramsdell, SendMail S/MIME WG Blake Ramsdell, SendMail
Internet Draft Sean Turner, IECA Internet Draft Sean Turner, IECA
Intended Status: Standard Track June 3, 2008 Intended Status: Standard Track June 30, 2008
Obsoletes: 3851 (when approved) Obsoletes: 3851 (when approved)
Expires: December 3, 2008 Expires: December 30, 2008
Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2
Message Specification Message Specification
draft-ietf-smime-3851bis-03.txt draft-ietf-smime-3851bis-04.txt
Status of this Memo Status of this Memo
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Abstract Abstract
This document defines Secure/Multipurpose Internet Mail Extensions This document defines Secure/Multipurpose Internet Mail Extensions
(S/MIME) version 3.2. S/MIME provides a consistent way to send and (S/MIME) version 3.2. S/MIME provides a consistent way to send and
receive secure MIME data. Digital signatures provide authentication, receive secure MIME data. Digital signatures provide authentication,
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This draft is being discussed on the 'ietf-smime' mailing list. To This draft is being discussed on the 'ietf-smime' mailing list. To
subscribe, send a message to ietf-smime-request@imc.org with the subscribe, send a message to ietf-smime-request@imc.org with the
single word subscribe in the body of the message. There is a Web site single word subscribe in the body of the message. There is a Web site
for the mailing list at <http://www.imc.org/ietf-smime/>. for the mailing list at <http://www.imc.org/ietf-smime/>.
Table of Contents Table of Contents
1. Introduction...................................................3 1. Introduction...................................................3
1.1. Specification Overview....................................4 1.1. Specification Overview....................................4
1.2. Definitions...............................................5 1.2. Definitions...............................................4
1.3. Conventions used in this document.........................6 1.3. Conventions used in this document.........................5
1.4. Compatibility with Prior Practice of S/MIME...............6 1.4. Compatibility with Prior Practice of S/MIME...............6
1.5. Changes From S/MIME v3 to S/MIME v3.1.....................6 1.5. Changes From S/MIME v3 to S/MIME v3.1.....................6
1.6. Changes Since S/MIME v3.1.................................7 1.6. Changes Since S/MIME v3.1.................................7
2. CMS Options....................................................8 2. CMS Options....................................................8
2.1. DigestAlgorithmIdentifier.................................8 2.1. DigestAlgorithmIdentifier.................................8
2.2. SignatureAlgorithmIdentifier..............................8 2.2. SignatureAlgorithmIdentifier..............................8
2.3. KeyEncryptionAlgorithmIdentifier..........................9 2.3. KeyEncryptionAlgorithmIdentifier..........................9
2.4. General Syntax............................................9 2.4. General Syntax............................................9
2.4.1. Data Content Type....................................9
2.4.2. SignedData Content Type..............................9
2.4.3. EnvelopedData Content Type..........................10
2.4.4. CompressedData Content Type.........................10
2.5. Attributes and the SignerInfo Type.......................10 2.5. Attributes and the SignerInfo Type.......................10
2.5.1. Signing-Time Attribute..............................11 2.5.1. Signing-Time Attribute..............................11
2.5.2. SMIMECapabilities Attribute.........................11 2.5.2. SMIMECapabilities Attribute.........................12
2.5.3. Encryption Key Preference Attribute.................12 2.5.3. Encryption Key Preference Attribute.................13
2.5.3.1. Selection of Recipient Key Management
Certificate....................................13
2.6. SignerIdentifier SignerInfo Type.........................14 2.6. SignerIdentifier SignerInfo Type.........................14
2.7. ContentEncryptionAlgorithmIdentifier.....................14 2.7. ContentEncryptionAlgorithmIdentifier.....................15
2.7.1. Deciding Which Encryption Method To Use.............14 2.7.1. Deciding Which Encryption Method To Use.............15
2.7.1.1. Rule 1: Known Capabilities.....................15
2.7.1.2. Rule 2: Unknown Capabilities, Unknown Version
of S/MIME..............................16
2.7.2. Choosing Weak Encryption............................16 2.7.2. Choosing Weak Encryption............................16
2.7.3. Multiple Recipients.................................16 2.7.3. Multiple Recipients.................................17
3. Creating S/MIME Messages......................................16 3. Creating S/MIME Messages......................................17
3.1. Preparing the MIME Entity for Signing, Enveloping or 3.1. Preparing the MIME Entity for Signing, Enveloping or
Compressing..............................................17 Compressing..............................................17
3.1.1. Canonicalization....................................18 3.2. The application/pkcs7-mime Media Type....................22
3.1.2. Transfer Encoding...................................19
3.1.3. Transfer Encoding for Signing Using
multipart/signed....................................20
3.1.4. Sample Canonical MIME Entity........................20
3.2. The application/pkcs7-mime Media Type....................21
3.2.1. The name and filename Parameters....................22
3.2.2. The smime-type parameter............................23
3.3. Creating an Enveloped-only Message.......................24 3.3. Creating an Enveloped-only Message.......................24
3.4. Creating a Signed-only Message...........................24 3.4. Creating a Signed-only Message...........................25
3.4.1. Choosing a Format for Signed-only Messages..........25 3.4.1. Choosing a Format for Signed-only Messages..........25
3.4.2. Signing Using application/pkcs7-mime with 3.4.2. Signing Using application/pkcs7-mime with
SignedData..........................................25 SignedData..........................................26
3.4.3. Signing Using the multipart/signed Format...........26 3.4.3. Signing Using the multipart/signed Format...........26
3.4.3.1. The application/pkcs7-signature Media Type.....26 3.5. Creating an Compressed-only Message......................29
3.4.3.2. Creating a multipart/signed Message............26
3.4.3.3. Sample multipart/signed Message................28
3.5. Creating an Compressed-only Message......................28
3.6. Multiple Operations......................................29 3.6. Multiple Operations......................................29
3.7. Creating a Certificate Management Message................30 3.7. Creating a Certificate Management Message................30
3.8. Registration Requests....................................30 3.8. Registration Requests....................................31
3.9. Identifying an S/MIME Message............................31 3.9. Identifying an S/MIME Message............................31
4. Certificate Processing........................................31 4. Certificate Processing........................................31
4.1. Key Pair Generation......................................31 4.1. Key Pair Generation......................................32
4.2. Signature Generation.....................................32 4.2. Signature Generation.....................................32
4.3. Signature Verification...................................32 4.3. Signature Verification...................................32
4.4. Encryption...............................................32 4.4. Encryption...............................................32
4.5. Decryption...............................................32 4.5. Decryption...............................................33
5. IANA Considerations...........................................32 5. IANA Considerations...........................................34
6. Security Considerations.......................................33 5.1. Media Type for application/pkcs7-mime....................34
Appendix A. ASN.1 Module.........................................35 5.2. Media Type for application/pkcs7-signature...............35
Appendix B. References...........................................37 6. Security Considerations.......................................36
B.1. Normative References.....................................37 7. References....................................................38
B.2. Informative References...................................39 7.1. Normative References.....................................38
Appendix C. Acknowledgements.....................................40 7.2. Informative References...................................40
Appendix A. ASN.1 Module.........................................42
Appendix B. Moving S/MIME v2 Message Specification to
Historic Status......................................44
Appendix C. Acknowledgements.....................................45
1. Introduction 1. Introduction
S/MIME (Secure/Multipurpose Internet Mail Extensions) provides a S/MIME (Secure/Multipurpose Internet Mail Extensions) provides a
consistent way to send and receive secure MIME data. Based on the consistent way to send and receive secure MIME data. Based on the
popular Internet MIME standard, S/MIME provides the following popular Internet MIME standard, S/MIME provides the following
cryptographic security services for electronic messaging cryptographic security services for electronic messaging
applications: authentication, message integrity and non-repudiation applications: authentication, message integrity and non-repudiation
of origin (using digital signatures), and data confidentiality (using of origin (using digital signatures), and data confidentiality (using
encryption). As a supplementary service, S/MIME provides for message encryption). As a supplementary service, S/MIME provides for message
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1.2. Definitions 1.2. Definitions
For the purposes of this specification, the following definitions For the purposes of this specification, the following definitions
apply. apply.
ASN.1: Abstract Syntax Notation One, as defined in CCITT X.208 ASN.1: Abstract Syntax Notation One, as defined in CCITT X.208
[X.208-88]. [X.208-88].
BER: Basic Encoding Rules for ASN.1, as defined in CCITT X.209 BER: Basic Encoding Rules for ASN.1, as defined in CCITT X.209
[X.209-88]. [X.690-02].
Certificate: A type that binds an entity's name to a public key with Certificate: A type that binds an entity's name to a public key with
a digital signature. a digital signature.
DER: Distinguished Encoding Rules for ASN.1, as defined in CCITT DER: Distinguished Encoding Rules for ASN.1, as defined in CCITT
X.509 [X.509-88]. X.509 [X.690-02].
7-bit data: Text data with lines less than 998 characters long, where 7-bit data: Text data with lines less than 998 characters long, where
none of the characters have the 8th bit set, and there are no NULL none of the characters have the 8th bit set, and there are no NULL
characters. <CR> and <LF> occur only as part of a <CR><LF> end of characters. <CR> and <LF> occur only as part of a <CR><LF> end of
line delimiter. line delimiter.
8-bit data: Text data with lines less than 998 characters, and where 8-bit data: Text data with lines less than 998 characters, and where
none of the characters are NULL characters. <CR> and <LF> occur only none of the characters are NULL characters. <CR> and <LF> occur only
as part of a <CR><LF> end of line delimiter. as part of a <CR><LF> end of line delimiter.
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expect that this requirement will no longer be a MUST in a future expect that this requirement will no longer be a MUST in a future
document. Although its status will be determined at a later document. Although its status will be determined at a later
time, it is reasonable to expect that if a future revision of a time, it is reasonable to expect that if a future revision of a
document alters the status of a MUST- requirement, it will remain document alters the status of a MUST- requirement, it will remain
at least a SHOULD or a SHOULD-. at least a SHOULD or a SHOULD-.
1.4. Compatibility with Prior Practice of S/MIME 1.4. Compatibility with Prior Practice of S/MIME
S/MIME version 3.2 agents SHOULD attempt to have the greatest S/MIME version 3.2 agents SHOULD attempt to have the greatest
interoperability possible with agents for prior versions of S/MIME. interoperability possible with agents for prior versions of S/MIME.
S/MIME version 2 is described in RFC 2311 through RFC 2315 , S/MIME S/MIME version 2 is described in RFC 2311 through RFC 2315 inclusive
version 3 is described in RFC 2630 through RFC 2634, and S/MIME [SMIMEv2], S/MIME version 3 is described in RFC 2630 through RFC 2634
version 3.1 is described in RFC 3850, RFC 3851, and RFC 2634. RFC inclusive [SMIMEv3], and S/MIME version 3.1 is described in RFC 3850
2311 also has historical information about the development of S/MIME. through RFC 3852 and RFC 2634 [SMIMEv3.1]. RFC 2311 also has
historical information about the development of S/MIME.
1.5. Changes From S/MIME v3 to S/MIME v3.1 1.5. Changes From S/MIME v3 to S/MIME v3.1
The RSA public key algorithm was changed to a MUST implement key The RSA public key algorithm was changed to a MUST implement key
wrapping algorithm, and the Diffie-Hellman algorithm changed to a wrapping algorithm, and the Diffie-Hellman algorithm changed to a
SHOULD implement. SHOULD implement.
The AES symmetric encryption algorithm has been included as a SHOULD The AES symmetric encryption algorithm has been included as a SHOULD
implement. implement.
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has been added. has been added.
Use of the CompressedData CMS type is allowed, along with required Use of the CompressedData CMS type is allowed, along with required
media type and file extension additions. media type and file extension additions.
1.6. Changes Since S/MIME v3.1 1.6. Changes Since S/MIME v3.1
Editorial changes, e.g., replaced "MIME type" with "media type", Editorial changes, e.g., replaced "MIME type" with "media type",
content-type with Content-Type. content-type with Content-Type.
Moved "Conventions Used in This Document to Section 1.2." Added Moved "Conventions Used in This Document" to Section 1.2. Added
definitions for SHOULD+, SHOULD-, and MUST-. definitions for SHOULD+, SHOULD-, and MUST-.
Sec 1.1 and Appendix A: Added references to RFCs for RSA-PSS, RSA- Sec 1.1 and Appendix A: Added references to RFCs for RSA-PSS, RSA-
OAEP, and SHA2 CMS Algorithms. Added CMS Multiple Signers OAEP, and SHA2 CMS Algorithms. Added CMS Multiple Signers
Clarification to CMS reference. Clarification to CMS reference.
Sec 1.3: Added references to S/MIME MSG 3.1 RFCs. Sec 1.3: Added references to S/MIME MSG 3.1 RFCs.
Sec 2.1 (digest algorithm): SHA-256 added as MUST, SHA-1 and MD5 made Sec 2.1 (digest algorithm): SHA-256 added as MUST, SHA-1 and MD5 made
SHOULD-. SHOULD-.
Sec 2.2 (signature algorithms): RSA with SHA256 added as the MUST, Sec 2.2 (signature algorithms): RSA with SHA-256 added as the MUST,
RSA with SHA-1 changed to MUST-, DSA with SHA-1, and RSA with MD5 RSA with SHA-1, DSA with SHA-1, and RSA with MD5 changed to SHOULD-,
changed to SHOULD-, and RSA-PSS with SHA-256. Also added note about and RSA-PSS with SHA-256 added as SHOULD+. Also added note about what
what S/MIME v3.1 clients support. S/MIME v3.1 clients support.
Sec 2.3 (key encryption): DH changed to SHOULD- and RSA-OAEP added as Sec 2.3 (key encryption): DH changed to SHOULD- and RSA-OAEP added as
SHOULD+. SHOULD+.
Sec 2.5.1: Added requirement that receiving agents MUST support both Sec 2.5.1: Added requirement that receiving agents MUST support both
GeneralizedTime and UTCTime. GeneralizedTime and UTCTime.
Sec 2.5.2: Replaced reference "sha1WithRSAEncrption" with Sec 2.5.2: Replaced reference "sha1WithRSAEncrption" with
"sha256WithRSAEncryption" and "AES-CBC". "sha256WithRSAEncryption", "DES-3EDE-CBC" and "AES-128 CBC", and
deleted the RC5 example.
Sec 2.5.2.1, 2.7, 2.7.1, Appendix A: reference to RC2/40 removed. Sec 2.5.2.1, 2.7, 2.7.1, Appendix A: references to RC2/40 removed.
Sec 2.7 (content encryption): AES-128 CBC added as MUST, AES-192 and Sec 2.7 (content encryption): AES-128 CBC added as MUST, AES-192 and
AES-256 CBC SHOULD+, tripleDES now SHOULD-. AES-256 CBC SHOULD+, tripleDES now SHOULD-.
Sec 2.7.1: Updated pointers from 2.7.2.1 through 2.7.2.4 to 2.7.1.1
to 2.7.1.2.
Sec 3.2.2: Replaced "encrypted" with "enveloped." Update OID example
to use AES-128 CBC oid.
Sec 4: Updated reference to CERT v3.2. Sec 4: Updated reference to CERT v3.2.
Sec 4.1: Updated RSA key size discussion. Moved last 4 sentences to Sec 4.1: Updated RSA key size discussion. Moved last four sentences
security considerations. Updated reference to randomness requirements to security considerations. Updated reference to randomness
for security. requirements for security.
Sec 5: Added IANA registration templates to update media type
registry to point to this document as opposed to RFC 2311.
Sec 6: Updated Security Considerations.
Sec 7: Moved references from Appendix B to this section. Update
references. Added informational references to SMIMEv2, SMIMEv3, and
SMIMEv3.1.
App B: Added Appendix B to move S/MIME v2 to historic status.
2. CMS Options 2. CMS Options
CMS allows for a wide variety of options in content, attributes, and CMS allows for a wide variety of options in content, attributes, and
algorithm support. This section puts forth a number of support algorithm support. This section puts forth a number of support
requirements and recommendations in order to achieve a base level of requirements and recommendations in order to achieve a base level of
interoperability among all S/MIME implementations. [CMSALG] and [CMS- interoperability among all S/MIME implementations. [CMSALG] and [CMS-
SHA2] provides additional details regarding the use of the SHA2] provides additional details regarding the use of the
cryptographic algorithms. [ESS] provides additional details cryptographic algorithms. [ESS] provides additional details
regarding the use of additional attributes. regarding the use of additional attributes.
2.1. DigestAlgorithmIdentifier 2.1. DigestAlgorithmIdentifier
Sending and receiving agents MUST support SHA-256 [CMS-SHA2] and Sending and receiving agents MUST support SHA-256 [CMS-SHA2] and
SHOULD- support SHA-1 [CMSALG]. Receiving agents SHOULD- support MD5 SHOULD- support SHA-1 [CMSALG]. Receiving agents SHOULD- support MD5
[CMSALG] for the purpose of providing backward compatibility with [CMSALG] for the purpose of providing backward compatibility with
MD5-digested S/MIME v2 SignedData objects. MD5-digested S/MIME v2 SignedData objects.
2.2. SignatureAlgorithmIdentifier 2.2. SignatureAlgorithmIdentifier
Receiving and sending agents: Receiving agents:
- MUST support RSA with SHA-256, as specified in [CMS-SHA2] - MUST support RSA with SHA-256, as specified in [CMS-SHA2]
- MUST- support RSA with SHA-1, as specified in [CMSALG]
- SHOULD+ support RSA-PSS with SHA-256, as specified in [RSAPSS] - SHOULD+ support RSA-PSS with SHA-256, as specified in [RSAPSS]
- SHOULD- support RSA with SHA-1, as specified in [CMSALG]
- SHOULD- support DSA with SHA-1, as specified in [CMSALG] - SHOULD- support DSA with SHA-1, as specified in [CMSALG]
- SHOULD- support RSA with MD5, as specified in [CMSALG]. - SHOULD- support RSA with MD5, as specified in [CMSALG].
Note that S/MIME v3.1 client support verifying id-dsa-with-sha1 and Sending agents:
- MUST support RSA with SHA-256, as specified in [CMS-SHA2]
- SHOULD+ support RSA-PSS with SHA-256, as specified in [RSAPSS]
- SHOULD- support RSA with SHA-1 or DSA with SHA-1, as specified in
[CMSALG]
- SHOULD- support RSA with MD5, as specified in [CMSALG].
Note that S/MIME v3.1 clients support verifying id-dsa-with-sha1 and
rsaEncryption and might not implement sha256withRSAEncryption. Note rsaEncryption and might not implement sha256withRSAEncryption. Note
that S/MIME v3 clients might only implement signing or signature that S/MIME v3 clients might only implement signing or signature
verification using id-dsa-with-sha1, and might also use id-dsa as an verification using id-dsa-with-sha1, and might also use id-dsa as an
AlgorithmIdentifier in this field. Receiving clients SHOULD AlgorithmIdentifier in this field. Receiving clients SHOULD
recognize id-dsa as equivalent to id-dsa-with-sha1, and sending recognize id-dsa as equivalent to id-dsa-with-sha1, and sending
clients MUST use id-dsa-with-sha1 if using that algorithm. Also note clients MUST use id-dsa-with-sha1 if using that algorithm. Also note
that S/MIME v2 clients are only required to verify digital signatures that S/MIME v2 clients are only required to verify digital signatures
using the rsaEncryption algorithm with SHA-1 or MD5, and might not using the rsaEncryption algorithm with SHA-1 or MD5, and might not
implement id-dsa-with-sha1 or id-dsa at all. implement id-dsa-with-sha1 or id-dsa at all.
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If YY is greater than or equal to 50, the year is interpreted as If YY is greater than or equal to 50, the year is interpreted as
19YY; if YY is less than 50, the year is interpreted as 20YY. 19YY; if YY is less than 50, the year is interpreted as 20YY.
Receiving agents MUST be able to process signing-time attributes that Receiving agents MUST be able to process signing-time attributes that
are encoded in either UTCTime or GeneralizedTime. are encoded in either UTCTime or GeneralizedTime.
2.5.2. SMIMECapabilities Attribute 2.5.2. SMIMECapabilities Attribute
The SMIMECapabilities attribute includes signature algorithms (such The SMIMECapabilities attribute includes signature algorithms (such
as "sha256WithRSAEncryption"), symmetric algorithms (such as "AES- as "sha256WithRSAEncryption"), symmetric algorithms (such as "AES-128
CBC"), and key encipherment algorithms (such as "rsaEncryption"). CBC"), and key encipherment algorithms (such as "rsaEncryption").
There are also several identifiers which indicate support for other There are also several identifiers which indicate support for other
optional features such as binary encoding and compression. The optional features such as binary encoding and compression. The
SMIMECapabilities were designed to be flexible and extensible so SMIMECapabilities were designed to be flexible and extensible so
that, in the future, a means of identifying other capabilities and that, in the future, a means of identifying other capabilities and
preferences such as certificates can be added in a way that will not preferences such as certificates can be added in a way that will not
cause current clients to break. cause current clients to break.
If present, the SMIMECapabilities attribute MUST be a If present, the SMIMECapabilities attribute MUST be a
SignedAttribute; it MUST NOT be an UnsignedAttribute. CMS defines SignedAttribute; it MUST NOT be an UnsignedAttribute. CMS defines
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supports, and need not list all its capabilities so that the supports, and need not list all its capabilities so that the
capabilities list doesn't get too long. In an SMIMECapabilities capabilities list doesn't get too long. In an SMIMECapabilities
attribute, the object identifiers (OIDs) are listed in order of their attribute, the object identifiers (OIDs) are listed in order of their
preference, but SHOULD be separated logically along the lines of preference, but SHOULD be separated logically along the lines of
their categories (signature algorithms, symmetric algorithms, key their categories (signature algorithms, symmetric algorithms, key
encipherment algorithms, etc.) encipherment algorithms, etc.)
The structure of the SMIMECapabilities attribute is to facilitate The structure of the SMIMECapabilities attribute is to facilitate
simple table lookups and binary comparisons in order to determine simple table lookups and binary comparisons in order to determine
matches. For instance, the DER-encoding for the SMIMECapability for matches. For instance, the DER-encoding for the SMIMECapability for
DES EDE3 CBC MUST be identically encoded regardless of the AES-128 CBC MUST be identically encoded regardless of the
implementation. Because of the requirement for identical encoding, implementation. Because of the requirement for identical encoding,
individuals documenting algorithms to be used in the individuals documenting algorithms to be used in the
SMIMECapabilities attribute SHOULD explicitly document the correct SMIMECapabilities attribute SHOULD explicitly document the correct
byte sequence for the common cases. byte sequence for the common cases.
For any capability, the associated parameters for the OID MUST For any capability, the associated parameters for the OID MUST
specify all of the parameters necessary to differentiate between two specify all of the parameters necessary to differentiate between two
instances of the same algorithm. For instance, the number of rounds instances of the same algorithm.
and the block size for RC5 needs to be specified in addition to the
key length.
The OIDs that correspond to algorithms SHOULD use the same OID as the The OIDs that correspond to algorithms SHOULD use the same OID as the
actual algorithm, except in the case where the algorithm usage is actual algorithm, except in the case where the algorithm usage is
ambiguous from the OID. For instance, in an earlier specification, ambiguous from the OID. For instance, in an earlier specification,
rsaEncryption was ambiguous because it could refer to either a rsaEncryption was ambiguous because it could refer to either a
signature algorithm or a key encipherment algorithm. In the event signature algorithm or a key encipherment algorithm. In the event
that an OID is ambiguous, it needs to be arbitrated by the maintainer that an OID is ambiguous, it needs to be arbitrated by the maintainer
of the registered SMIMECapabilities list as to which type of of the registered SMIMECapabilities list as to which type of
algorithm will use the OID, and a new OID MUST be allocated under the algorithm will use the OID, and a new OID MUST be allocated under the
smimeCapabilities OID to satisfy the other use of the OID. smimeCapabilities OID to satisfy the other use of the OID.
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recipient, the following steps SHOULD be followed: recipient, the following steps SHOULD be followed:
- If an SMIMEEncryptionKeyPreference attribute is found in a - If an SMIMEEncryptionKeyPreference attribute is found in a
SignedData object received from the desired recipient, this SignedData object received from the desired recipient, this
identifies the X.509 certificate that SHOULD be used as the X.509 identifies the X.509 certificate that SHOULD be used as the X.509
key management certificate for the recipient. key management certificate for the recipient.
- If an SMIMEEncryptionKeyPreference attribute is not found in a - If an SMIMEEncryptionKeyPreference attribute is not found in a
SignedData object received from the desired recipient, the set of SignedData object received from the desired recipient, the set of
X.509 certificates SHOULD be searched for a X.509 certificate X.509 certificates SHOULD be searched for a X.509 certificate
with the same subject name as the signing of a X.509 certificate with the same subject name as the signer of a X.509 certificate
which can be used for key management. which can be used for key management.
- Or use some other method of determining the user's key management - Or use some other method of determining the user's key management
key. If a X.509 key management certificate is not found, then key. If a X.509 key management certificate is not found, then
encryption cannot be done with the signer of the message. If encryption cannot be done with the signer of the message. If
multiple X.509 key management certificates are found, the S/MIME multiple X.509 key management certificates are found, the S/MIME
agent can make an arbitrary choice between them. agent can make an arbitrary choice between them.
2.6. SignerIdentifier SignerInfo Type 2.6. SignerIdentifier SignerInfo Type
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messages. messages.
Before sending a message, the sending agent MUST decide whether it is Before sending a message, the sending agent MUST decide whether it is
willing to use weak encryption for the particular data in the willing to use weak encryption for the particular data in the
message. If the sending agent decides that weak encryption is message. If the sending agent decides that weak encryption is
unacceptable for this data, then the sending agent MUST NOT use a unacceptable for this data, then the sending agent MUST NOT use a
weak algorithm. The decision to use or not use weak encryption weak algorithm. The decision to use or not use weak encryption
overrides any other decision in this section about which encryption overrides any other decision in this section about which encryption
algorithm to use. algorithm to use.
Sections 2.7.2.1 through 2.7.2.4 describe the decisions a sending Sections 2.7.1.1 through 2.7.1.2 describe the decisions a sending
agent SHOULD use in deciding which type of encryption will be applied agent SHOULD use in deciding which type of encryption will be applied
to a message. These rules are ordered, so the sending agent SHOULD to a message. These rules are ordered, so the sending agent SHOULD
make its decision in the order given. make its decision in the order given.
2.7.1.1. Rule 1: Known Capabilities 2.7.1.1. Rule 1: Known Capabilities
If the sending agent has received a set of capabilities from the If the sending agent has received a set of capabilities from the
recipient for the message the agent is about to encrypt, then the recipient for the message the agent is about to encrypt, then the
sending agent SHOULD use that information by selecting the first sending agent SHOULD use that information by selecting the first
capability in the list (that is, the capability most preferred by the capability in the list (that is, the capability most preferred by the
skipping to change at page 16, line 15 skipping to change at page 16, line 42
2.7.1.2. Rule 2: Unknown Capabilities, Unknown Version of S/MIME 2.7.1.2. Rule 2: Unknown Capabilities, Unknown Version of S/MIME
If the following two conditions are met: If the following two conditions are met:
- The sending agent has no knowledge of the encryption capabilities - The sending agent has no knowledge of the encryption capabilities
of the recipient, and of the recipient, and
- The sending agent has no knowledge of the version of S/MIME of the - The sending agent has no knowledge of the version of S/MIME of the
recipient, recipient,
then the sending agent SHOULD use AES 128 because it is a stronger then the sending agent SHOULD use AES-128 because it is a stronger
algorithm and is required by S/MIME v3.2. If the sending agent algorithm and is required by S/MIME v3.2. If the sending agent
chooses not to use AES 128 in this step, it SHOULD use tripleDES. chooses not to use AES-128 in this step, it SHOULD use tripleDES.
2.7.2. Choosing Weak Encryption 2.7.2. Choosing Weak Encryption
All algorithms that use 40 bit keys are considered by many to be weak All algorithms that use 40 bit keys are considered by many to be weak
encryption. A sending agent that is controlled by a human SHOULD encryption. A sending agent that is controlled by a human SHOULD
allow a human sender to determine the risks of sending data using allow a human sender to determine the risks of sending data using a
weak encryption algorithm before sending the data, and possibly allow weak encryption algorithm before sending the data, and possibly allow
the human to use a stronger encryption method such as tripleDES or the human to use a stronger encryption method such as tripleDES or
AES. AES.
2.7.3. Multiple Recipients 2.7.3. Multiple Recipients
If a sending agent is composing an encrypted message to a group of If a sending agent is composing an encrypted message to a group of
recipients where the encryption capabilities of some of the recipients where the encryption capabilities of some of the
recipients do not overlap, the sending agent is forced to send more recipients do not overlap, the sending agent is forced to send more
than one message. Please note that if the sending agent chooses to than one message. Please note that if the sending agent chooses to
skipping to change at page 18, line 23 skipping to change at page 18, line 47
canonical form. canonical form.
Step 3. Appropriate transfer encoding is applied to the leaves Step 3. Appropriate transfer encoding is applied to the leaves
of the MIME entity. of the MIME entity.
When an S/MIME message is received, the security services on the When an S/MIME message is received, the security services on the
message are processed, and the result is the MIME entity. That MIME message are processed, and the result is the MIME entity. That MIME
entity is typically passed to a MIME-capable user agent where it is entity is typically passed to a MIME-capable user agent where it is
further decoded and presented to the user or receiving application. further decoded and presented to the user or receiving application.
In order to protect outer, non-content related message headers (for In order to protect outer, non-content related message header fields
instance, the "Subject", "To", "From" and "Cc" fields), the sending (for instance, the "Subject", "To", "From" and "Cc" fields), the
client MAY wrap a full MIME message in a message/rfc822 wrapper in sending client MAY wrap a full MIME message in a message/rfc822
order to apply S/MIME security services to these header fields. It wrapper in order to apply S/MIME security services to these header
is up to the receiving client to decide how to present this "inner" fields. It is up to the receiving client to decide how to present
header along with the unprotected "outer" header. this "inner" header along with the unprotected "outer" header.
When an S/MIME message is received, if the top-level protected MIME When an S/MIME message is received, if the top-level protected MIME
entity has a Content-Type of message/rfc822, it can be assumed that entity has a Content-Type of message/rfc822, it can be assumed that
the intent was to provide header protection. This entity SHOULD be the intent was to provide header protection. This entity SHOULD be
presented as the top-level message, taking into account header presented as the top-level message, taking into account header
merging issues as previously discussed. merging issues as previously discussed.
3.1.1. Canonicalization 3.1.1. Canonicalization
Each MIME entity MUST be converted to a canonical form that is Each MIME entity MUST be converted to a canonical form that is
skipping to change at page 23, line 42 skipping to change at page 24, line 19
then two values for smime-type SHOULD be assigned "signed-*" and then two values for smime-type SHOULD be assigned "signed-*" and
"encrypted-*". If one operation can be assigned then this can be "encrypted-*". If one operation can be assigned then this can be
omitted. Thus since "certs-only" can only be signed, "signed-" omitted. Thus since "certs-only" can only be signed, "signed-"
is omitted. is omitted.
2. A common string for a content OID SHOULD be assigned. We use 2. A common string for a content OID SHOULD be assigned. We use
"data" for the id-data content OID when MIME is the inner "data" for the id-data content OID when MIME is the inner
content. content.
3. If no common string is assigned, then the common string of 3. If no common string is assigned, then the common string of
"OID.<oid>" is recommended (for example, "OID.1.3.6.1.5.5.7.6.1" "OID.<oid>" is recommended (for example,
would be DES40). "OID.2.16.840.1.101.3.4.1.2" would be AES-128 CBC).
It is explicitly intended that this field be a suitable hint for mail It is explicitly intended that this field be a suitable hint for mail
client applications to indicate whether a message is "signed" or client applications to indicate whether a message is "signed" or
"encrypted" without having to tunnel into the CMS payload. "encrypted" without having to tunnel into the CMS payload.
3.3. Creating an Enveloped-only Message 3.3. Creating an Enveloped-only Message
This section describes the format for enveloping a MIME entity This section describes the format for enveloping a MIME entity
without signing it. It is important to note that sending enveloped without signing it. It is important to note that sending enveloped
but not signed messages does not provide for data integrity. It is but not signed messages does not provide for data integrity. It is
skipping to change at page 27, line 44 skipping to change at page 28, line 15
SHA-384 sha384 SHA-384 sha384
SHA-512 sha512 SHA-512 sha512
Any other (defined separately in algorithm profile or "unknown" Any other (defined separately in algorithm profile or "unknown"
if not defined) if not defined)
(Historical note: some early implementations of S/MIME emitted and (Historical note: some early implementations of S/MIME emitted and
expected "rsa-md5" and "rsa-sha1" for the micalg parameter.) expected "rsa-md5" and "rsa-sha1" for the micalg parameter.)
Receiving agents SHOULD be able to recover gracefully from a micalg Receiving agents SHOULD be able to recover gracefully from a micalg
parameter value that they do not recognize. parameter value that they do not recognize.
The SHA-224 algorithm, SHA-384 and SHA-512 algorithms [FIPS180-3] are The SHA-224, SHA-384, and SHA-512 algorithms [FIPS180-3] are not
not currently recommended in S/MIME, and are included here for currently recommended in S/MIME, and are included here for
completeness. completeness.
3.4.3.3. Sample multipart/signed Message 3.4.3.3. Sample multipart/signed Message
Content-Type: multipart/signed; Content-Type: multipart/signed;
protocol="application/pkcs7-signature"; protocol="application/pkcs7-signature";
micalg=sha1; boundary=boundary42 micalg=sha1; boundary=boundary42
--boundary42 --boundary42
Content-Type: text/plain Content-Type: text/plain
skipping to change at page 30, line 43 skipping to change at page 31, line 13
"certs-only". The file extension for this type of message is ".p7c". "certs-only". The file extension for this type of message is ".p7c".
3.8. Registration Requests 3.8. Registration Requests
A sending agent that signs messages MUST have a certificate for the A sending agent that signs messages MUST have a certificate for the
signature so that a receiving agent can verify the signature. There signature so that a receiving agent can verify the signature. There
are many ways of getting certificates, such as through an exchange are many ways of getting certificates, such as through an exchange
with a certificate authority, through a hardware token or diskette, with a certificate authority, through a hardware token or diskette,
and so on. and so on.
S/MIME v2 [SMIMEV2] specified a method for "registering" public keys S/MIME v2 [SMIMEv2] specified a method for "registering" public keys
with certificate authorities using an application/pkcs10 body part. with certificate authorities using an application/pkcs10 body part.
Since that time, the IETF PKIX Working Group has developed other Since that time, the IETF PKIX Working Group has developed other
methods for requesting certificates. However, S/MIME v3.2 does not methods for requesting certificates. However, S/MIME v3.2 does not
require a particular certificate request mechanism. require a particular certificate request mechanism.
3.9. Identifying an S/MIME Message 3.9. Identifying an S/MIME Message
Because S/MIME takes into account interoperation in non-MIME Because S/MIME takes into account interoperation in non-MIME
environments, several different mechanisms are employed to carry the environments, several different mechanisms are employed to carry the
type information, and it becomes a bit difficult to identify S/MIME type information, and it becomes a bit difficult to identify S/MIME
skipping to change at page 32, line 46 skipping to change at page 34, line 7
The following are the requirements for an S/MIME agent when The following are the requirements for an S/MIME agent when
establishing keys for content decryption using the RSA or DH establishing keys for content decryption using the RSA or DH
algorithms: algorithms:
512 <= key size <= 2048 : MUST (see Security Considerations) 512 <= key size <= 2048 : MUST (see Security Considerations)
2048 < key size <= 4096 : MAY (see Security Considerations) 2048 < key size <= 4096 : MAY (see Security Considerations)
5. IANA Considerations 5. IANA Considerations
None: All identifiers are already registered. Please remove this The following is intended to provide sufficient information to update
section prior to publication as an RFC. the media type registration for application/pkcs7-mime and
application/pkcs7-signature to refer to this document as opposed to
RFC 2311.
5.1. Media Type for application/pkcs7-mime
Type name: application
Subtype Name: pkcs7-mime
Required Parameters: NONE
Optional Parameters: smime-type/signed-data
smime-type/enveloped-data
smime-type/compressed-data
smime-type/certs-only
Encoding Considerations: See Section 3 of this document
Security Considerations: See Section 6 of this document
Interoperability Considerations: See Sections 1-6 of this document
Published Specification: RFC 2311, RFC 2633, and this document
Applications that use this media type: Security applications
Additional information: NONE
Person & email to contact for further information: S/MIME working
group chairs smime-chairs@tools.ietf.org
Intended usage: COMMON
Restrictions on usage: NONE
Author: Sean Turner
Change Controller: S/MIME working group delegated from the IESG
5.2. Media Type for application/pkcs7-signature
Type name: application
Subtype Name: pkcs7-signature
Required Parameters: NONE
Optional Parameters: NONE
Encoding Considerations: See Section 3 of this document
Security Considerations: See Section 6 of this document
Interoperability Considerations: See Sections 1-6 of this document
Published Specification: RFC 2311, RFC 2633, and this document
Applications that use this media type: Security applications
Additional information: NONE
Person & email to contact for further information: S/MIME working
group chairs smime-chairs@tools.ietf.org
Intended usage: COMMON
Restrictions on usage: NONE
Author: Sean Turner
Change Controller: S/MIME working group delegated from the IESG
6. Security Considerations 6. Security Considerations
Cryptographic algorithms will be broken or weakened over time. Cryptographic algorithms will be broken or weakened over time.
Implementers and users need to check that the cryptographic Implementers and users need to check that the cryptographic
algorithms listed in this document continue to provide the expected algorithms listed in this document continue to provide the expected
level of security. The IETF from time to time may issue documents level of security. The IETF from time to time may issue documents
dealing with the current state of the art. For example: dealing with the current state of the art. For example:
- The Million Message Attack described in RFC 3218 [MMA]. - The Million Message Attack described in RFC 3218 [MMA].
skipping to change at page 33, line 40 skipping to change at page 36, line 40
decryption if a recipient cannot process a message content. Thus, decryption if a recipient cannot process a message content. Thus,
choosing between different key sizes (or choosing whether to just use choosing between different key sizes (or choosing whether to just use
plaintext) is also impossible for most people or software. However, plaintext) is also impossible for most people or software. However,
decisions based on these criteria are made all the time, and decisions based on these criteria are made all the time, and
therefore this specification gives a framework for using those therefore this specification gives a framework for using those
estimates in choosing algorithms. estimates in choosing algorithms.
The choice of 1024 bits as the RSA, DSA, and DH asymmetric key size The choice of 1024 bits as the RSA, DSA, and DH asymmetric key size
in this specification is based on the desire to provide 80 bits of in this specification is based on the desire to provide 80 bits of
security. This key size seems prudent for the Internet based on security. This key size seems prudent for the Internet based on
Section 4.3 of [RFC3766]. There are other environments (e.g., Section 4.3 of [STRENGTH]. There are other environments (e.g.,
government, financial, and medical) that may consider this key size government, financial, and medical) that may consider this key size
to be inadequate. Likewise, there are other environments that may to be inadequate. Likewise, there are other environments that may
consider this key size to be excessive. consider this key size to be excessive.
Larger keys are not necessarily better keys. Larger keys take more Larger keys are not necessarily better keys. Larger keys take more
computational resources, and this can quickly become impractical. In computational resources, and this can quickly become impractical. In
fact, support for an excessively large key offers a denial of service fact, support for an excessively large key offers a denial of service
opportunity if the attacker can cause excessive cryptographic opportunity if the attacker can cause excessive cryptographic
processing by providing such a public key. One mitigation approach processing by providing such a public key. One mitigation approach
would require that the corresponding public key certificate be would require that the corresponding public key certificate be
validated to a trust anchor prior to use, thus ensuring that only validated to a trust anchor prior to use, thus ensuring that only
trusted public keys are used. However, some implementations may trusted public keys are used. However, some implementations may
choose to perform signature verification (or key establishment for choose to perform signature verification (or key establishment for
encryption) in parallel with certificate validation, even if encryption) in parallel with certificate validation, even if
certificate validation fails. In such cases, measures should be certificate validation fails. In such cases, measures should be
included to limit the impact, for example by limiting cryptographic included to limit the impact, for example by limiting cryptographic
processing time or requiring certificate validation prior to the use processing time or requiring certificate validation prior to the use
of large keys. of large keys.
Today, 512 bit RSA, DSA, and DH keys are considered by many experts Today, 512-bit RSA, DSA, and DH keys are considered by many experts
to be cryptographically insecure. to be cryptographically insecure.
Using weak cryptography in S/MIME offers little actual security over Using weak cryptography in S/MIME offers little actual security over
sending plaintext. However, other features of S/MIME, such as the sending plaintext. However, other features of S/MIME, such as the
specification of AES and the ability to announce stronger specification of AES and the ability to announce stronger
cryptographic capabilities to parties with whom you communicate, cryptographic capabilities to parties with whom you communicate,
allow senders to create messages that use strong encryption. Using allow senders to create messages that use strong encryption. Using
weak cryptography is never recommended unless the only alternative is weak cryptography is never recommended unless the only alternative is
no cryptography. When feasible, sending and receiving agents SHOULD no cryptography. When feasible, sending and receiving agents SHOULD
inform senders and recipients of the relative cryptographic strength inform senders and recipients of the relative cryptographic strength
skipping to change at page 35, line 5 skipping to change at page 38, line 5
channel might be able to determine the contents of the strongly- channel might be able to determine the contents of the strongly-
encrypted message by decrypting the weakly-encrypted version. In encrypted message by decrypting the weakly-encrypted version. In
other words, a sender SHOULD NOT send a copy of a message using other words, a sender SHOULD NOT send a copy of a message using
weaker cryptography than they would use for the original of the weaker cryptography than they would use for the original of the
message. message.
Modification of the ciphertext can go undetected if authentication is Modification of the ciphertext can go undetected if authentication is
not also used, which is the case when sending EnvelopedData without not also used, which is the case when sending EnvelopedData without
wrapping it in SignedData or enclosing SignedData within it. wrapping it in SignedData or enclosing SignedData within it.
Appendix A. ASN.1 Module 7. References
NOTE: The ASN.1 module contained herein is unchanged from [MSG3.1],
with the exception of a minor change to the prefersBinaryInside ASN.1
comment.
SecureMimeMessageV3dot1
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) msg-v3dot1(21) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS
-- Cryptographic Message Syntax
SubjectKeyIdentifier, IssuerAndSerialNumber,
RecipientKeyIdentifier
FROM CryptographicMessageSyntax
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) cms-2001(14) };
-- id-aa is the arc with all new authenticated and unauthenticated
-- attributes produced the by S/MIME Working Group
id-aa OBJECT IDENTIFIER ::= {iso(1) member-body(2) usa(840)
rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) attributes(2)}
-- S/MIME Capabilities provides a method of broadcasting the
-- symmetric capabilities understood. Algorithms SHOULD be ordered
-- by preference and grouped by type
smimeCapabilities OBJECT IDENTIFIER ::= {iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 15}
SMIMECapability ::= SEQUENCE {
capabilityID OBJECT IDENTIFIER,
parameters ANY DEFINED BY capabilityID OPTIONAL }
SMIMECapabilities ::= SEQUENCE OF SMIMECapability
-- Encryption Key Preference provides a method of broadcasting the
-- preferred encryption certificate.
id-aa-encrypKeyPref OBJECT IDENTIFIER ::= {id-aa 11}
SMIMEEncryptionKeyPreference ::= CHOICE {
issuerAndSerialNumber [0] IssuerAndSerialNumber,
receipentKeyId [1] RecipientKeyIdentifier,
subjectAltKeyIdentifier [2] SubjectKeyIdentifier
}
id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs9(9) 16 }
id-cap OBJECT IDENTIFIER ::= { id-smime 11 }
-- The preferBinaryInside OID indicates an ability to receive
-- messages with binary encoding inside the CMS wrapper
id-cap-preferBinaryInside OBJECT IDENTIFIER ::= { id-cap 1 }
-- The following list the OIDs to be used with S/MIME V3
-- Signature Algorithms Not Found in [CMSALG]
--
-- md2WithRSAEncryption OBJECT IDENTIFIER ::=
-- {iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1)
-- 2}
--
-- Other Signed Attributes
--
-- signingTime OBJECT IDENTIFIER ::=
-- {iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
-- 5}
-- See [CMS] for a description of how to encode the attribute
-- value.
SMIMECapabilitiesParametersForRC2CBC ::= INTEGER
-- (RC2 Key Length (number of bits))
END
Appendix B. References
B.1. Normative References 7.1. Normative References
[CERT32] Ramsdell, B., and S. Turner, "S/MIME Version 3.2 [CERT32] Ramsdell, B., and S. Turner, "S/MIME Version 3.2
Certificate Handling", work in progress. Certificate Handling", work in progress.
[CHARSETS] Character sets assigned by IANA. See [CHARSETS] Character sets assigned by IANA. See
http://www.iana.org/assignments/character-sets http://www.iana.org/assignments/character-sets
[CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC [CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
3852, July 2004. 3852, July 2004.
skipping to change at page 38, line 17 skipping to change at page 39, line 17
Message Bodies", RFC 2045, November 1996. Message Bodies", RFC 2045, November 1996.
Freed, N. and N. Borenstein, "Multipurpose Internet Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part Two: Media Types", RFC Mail Extensions (MIME) Part Two: Media Types", RFC
2046, November 1996. 2046, November 1996.
Moore, K., "MIME (Multipurpose Internet Mail Moore, K., "MIME (Multipurpose Internet Mail
Extensions) Part Three: Message Header Extensions for Extensions) Part Three: Message Header Extensions for
Non-ASCII Text", RFC 2047, November 1996. Non-ASCII Text", RFC 2047, November 1996.
Freed, N., Klensin, J., and J. Postel, "Multipurpose Freed, N., and J. Klensin, , "Multipurpose Internet
Internet Mail Extensions (MIME) Part Four: Mail Extensions (MIME) Part Four: Registration
Registration Procedures", BCP 13, RFC 2048, November Procedures", BCP 13, RFC 4289, December 2005.
1996.
Freed, N., and J. Klensin, "Media Type Specifications
and Registration Procedures ", BCP 13, RFC 4288,
December 2005.
Freed, N. and N. Borenstein, "Multipurpose Internet Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part Five: Conformance Criteria Mail Extensions (MIME) Part Five: Conformance Criteria
and Examples", RFC 2049, November 1996. and Examples", RFC 2049, November 1996.
[MIME-SECURE] Galvin, J., Murphy, S., Crocker, S., and N. Freed, [MIME-SECURE] Galvin, J., Murphy, S., Crocker, S., and N. Freed,
"Security Multiparts for MIME: Multipart/Signed and "Security Multiparts for MIME: Multipart/Signed and
Multipart/Encrypted", RFC 1847, October 1995. Multipart/Encrypted", RFC 1847, October 1995.
[MUSTSHOULD] Bradner, S., "Key words for use in RFCs to Indicate [MUSTSHOULD] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RANDOM] Eastlake 3rd, D., Crocker, S., and J. Schiller, [RANDOM] Eastlake 3rd, D., Crocker, S., and J. Schiller,
"Randomness Requirements for Security", BCP 106, RFC "Randomness Requirements for Security", BCP 106, RFC
4086, June 2005. 4086, June 2005.
[RSAPSS] Schaad, J., "Use of RSASA-PSS Signature Algorithm in [RSAPSS] Schaad, J., "Use of RSASA-PSS Signature Algorithm in
Cryptographic Message Syntax (CMS)", RFC 4056, June Cryptographic Message Syntax (CMS)", RFC 4056, June
2005. 2005.
[X.208-88] CCITT. Recommendation X.208: Specification of [RSAOAEP] Housley, R. "Use of the RSAES-OAEP Key Transport
Abstract Syntax Notation One (ASN.1). 1988. Algorithm in the Cryptographic Message Syntax (CMS)",
[X.208-88] ITU-T Recommandation X.208 (1988) | ISO/IEC 8824-
[X.209-88] CCITT. Recommendation X.209: Specification of Basic 1:1988. Specification of Abstract Syntax Notation One
Encoding Rules for Abstract Syntax Notation One (ASN.1).
(ASN.1). 1988.
[X.509-88] CCITT. Recommendation X.509: The Directory - [X.690-02] ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-
Authentication Framework. 1988. 1:2002. Information Technology - ASN.1 encoding
rules: Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER).
B.2. Informative References 7.2. Informative References
[DHSUB] Zuccherato, R., "Methods for Avoiding the "Small- [DHSUB] Zuccherato, R., "Methods for Avoiding the "Small-
Subgroup" Attacks on the Diffie-Hellman Key Agreement Subgroup" Attacks on the Diffie-Hellman Key Agreement
Method for S/MIME", RFC 2785, March 2000. Method for S/MIME", RFC 2785, March 2000.
[HASH-ATTACK] Hoffman, P., Schneier, B., "Attacks on Cryptographic
Hashes in Internet Protocols", RFC 4270, November
2005.
[MMA] Rescorla, E., "Preventing the Million Message Attack [MMA] Rescorla, E., "Preventing the Million Message Attack
on Cryptographic Message Syntax", RFC 3218, January on Cryptographic Message Syntax", RFC 3218, January
2002. 2002.
[MSG3.1] Ramsdell, B., "S/MIME Version 3.1 Message
Specification", RFC 3851, July 2004.
[PKCS-7] Kaliski, B., "PKCS #7: Cryptographic Message Syntax [PKCS-7] Kaliski, B., "PKCS #7: Cryptographic Message Syntax
Version 1.5", RFC 2315, March 1998. Version 1.5", RFC 2315, March 1998.
[SMIMEV2] Dusse, S., Hoffman, P., Ramsdell, B., Lundblade, L., [SMIMEv2] Dusse, S., Hoffman, P., Ramsdell, B., Lundblade, L.,
and L. Repka, "S/MIME Version 2 Message and L. Repka, "S/MIME Version 2 Message
Specification", RFC 2311, March 1998. Specification", RFC 2311, March 1998.
[HASH-ATTACK] Hoffman, P., Schneier, B., "Attacks on Cryptographic Dusse, S., Hoffman, P., Ramsdell, B., and J.
Hashes in Internet Protocols", RFC 4270, November Weinstein, "S/MIME Version 2 Certificate Handling",
2005. RFC 2312, March 1998.
Kaliski, B., "PKCS #1: RSA Encryption Version 1.5",
RFC 2313, March 1998.
Kaliski, B., "PKCS #10: Certificate Request Syntax
Version 1.5", RFC 2314, March 1998.
Kaliski, B., "PKCS #7: Certificate Message Syntax
Version 1.5", RFC 2314, March 1998.
[SMIMEv3] Housley, R., "Cryptographic Message Syntax", RFC 2630,
June 1999.
Rescorla, E., "Diffie-Hellman Key Agreement Method",
RFC 2631, June 1999.
Ramsdell, B., "S/MIME Version 3 Certificate Handling",
RFC 2632, June 1999.
Ramsdell, B., "S/MIME Version 3 Message
Specification", RFC 2633, June 1999.
Hoffman, P., "Enhanced Security Services for S/MIME",
RFC 2634, June 1999.
[SMIMEv3.1] Housley, R., "Cryptographic Message Syntax", RFC 3852,
July 2004.
Ramsdell, B., "S/MIME Version 3.1 Certificate
Handling", RFC 3850, July 2004.
Ramsdell, B., "S/MIME Version 3.1 Message
Specification", RFC 3851, July 2004.
Hoffman, P., "Enhanced Security Services for S/MIME",
RFC 2634, June 1999.
[STRENGTH] Orman, H., and P. Hoffman, "Determining Strengths For
Public Keys Used For Exchanging Symmetric Keys", BCP
86, RFC 3766, April 2004.
Appendix A. ASN.1 Module
NOTE: The ASN.1 module contained herein is unchanged from RFC 3851
[SMIMEv3], with the exception of a minor change to the
prefersBinaryInside ASN.1 comment.
SecureMimeMessageV3dot1
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) msg-v3dot1(21) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS
-- Cryptographic Message Syntax
SubjectKeyIdentifier, IssuerAndSerialNumber,
RecipientKeyIdentifier
FROM CryptographicMessageSyntax
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) cms-2001(14) };
-- id-aa is the arc with all new authenticated and unauthenticated
-- attributes produced the by S/MIME Working Group
id-aa OBJECT IDENTIFIER ::= {iso(1) member-body(2) usa(840)
rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) attributes(2)}
-- S/MIME Capabilities provides a method of broadcasting the
-- symmetric capabilities understood. Algorithms SHOULD be ordered
-- by preference and grouped by type
smimeCapabilities OBJECT IDENTIFIER ::= {iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 15}
SMIMECapability ::= SEQUENCE {
capabilityID OBJECT IDENTIFIER,
parameters ANY DEFINED BY capabilityID OPTIONAL }
SMIMECapabilities ::= SEQUENCE OF SMIMECapability
-- Encryption Key Preference provides a method of broadcasting the
-- preferred encryption certificate.
id-aa-encrypKeyPref OBJECT IDENTIFIER ::= {id-aa 11}
SMIMEEncryptionKeyPreference ::= CHOICE {
issuerAndSerialNumber [0] IssuerAndSerialNumber,
receipentKeyId [1] RecipientKeyIdentifier,
subjectAltKeyIdentifier [2] SubjectKeyIdentifier
}
id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs9(9) 16 }
id-cap OBJECT IDENTIFIER ::= { id-smime 11 }
-- The preferBinaryInside OID indicates an ability to receive
-- messages with binary encoding inside the CMS wrapper
id-cap-preferBinaryInside OBJECT IDENTIFIER ::= { id-cap 1 }
-- The following list the OIDs to be used with S/MIME V3
-- Signature Algorithms Not Found in [CMSALG]
--
-- md2WithRSAEncryption OBJECT IDENTIFIER ::=
-- {iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1)
-- 2}
--
-- Other Signed Attributes
--
-- signingTime OBJECT IDENTIFIER ::=
-- {iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
-- 5}
-- See [CMS] for a description of how to encode the attribute
-- value.
SMIMECapabilitiesParametersForRC2CBC ::= INTEGER
-- (RC2 Key Length (number of bits))
END
Appendix B. Moving S/MIME v2 Message Specification to Historic Status
The S/MIME v3 [SMIMEv3], v3.1 [SMIMEv3.1], and v3.2 (this document)
Message Specifications are backwards S/MIME v2 Message Specification
[SMIMEv2], with the exception of the algorithms (dropped RC2/40
requirement and added DSA and RSA-PSS requirements). Therefore, it is
recommended that RFC 2311 [SMIMEv2] be moved to Historic status.
Appendix C. Acknowledgements Appendix C. Acknowledgements
Many thanks go out to the other authors of the S/MIME Version 2 Many thanks go out to the other authors of the S/MIME Version 2
Message Specification RFC: Steve Dusse, Paul Hoffman, Laurence Message Specification RFC: Steve Dusse, Paul Hoffman, Laurence
Lundblade and Lisa Repka. Lundblade and Lisa Repka. Without v2, there wouldn't be a v3, v3.1 or
v3.2.
A number of the members of the S/MIME Working Group have also worked A number of the members of the S/MIME Working Group have also worked
very hard and contributed to this document. Any list of people is very hard and contributed to this document. Any list of people is
doomed to omission, and for that I apologize. In alphabetical order, doomed to omission, and for that I apologize. In alphabetical order,
the following people stand out in my mind due to the fact that they the following people stand out in my mind due to the fact that they
made direct contributions to this document. made direct contributions to this document.
Tony Capel, Piers Chivers, Dave Crocker, Bill Flanigan, Peter Tony Capel, Piers Chivers, Dave Crocker, Bill Flanigan, Peter
Gutmann, Paul Hoffman, Russ Housley, William Ottaway, John Pawling, Gutmann, Paul Hoffman, Russ Housley, William Ottaway, John Pawling,
and Jim Schaad. Jim Schaad, and Alfred Hoenes.
Author's Addresses Author's Addresses
Blake Ramsdell Blake Ramsdell
SendMail SendMail
Email: blake@sendmail.com Email: blake@sendmail.com
Sean Turner Sean Turner
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