draft-ietf-smime-aes-alg-00.txt   draft-ietf-smime-aes-alg-01.txt 
S/MIME Working Group J. Schaad S/MIME Working Group J. Schaad
Internet Draft Soaring Hawk Consulting Internet Draft Soaring Hawk Consulting
Document: draft-ietf-smime-aes-alg-00.txt November 2000 Document: draft-ietf-smime-aes-alg-01.txt R. Housley
Expires: May 31, 20001 Expires: September 2, 2001 RSA Laboratories
March 2001
Use of the Advanced Encryption Algorithm in CMS Use of the Advanced Encryption Algorithm in CMS
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1]. all provisions of Section 10 of RFC2026 [1].
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Comments or suggestions for improvement may be made on the "ietf- Comments or suggestions for improvement may be made on the "ietf-
smime" mailing list, or directly to the author. smime" mailing list, or directly to the author.
1. Abstract Abstract
This document specifies how to incorporate the Advanced Encryption This document specifies how to incorporate the Advanced Encryption
Standard (AES) candidate algorithm [AES] into the S/MIME Standard (AES) algorithm [AES] and RSAES-OAEP key transport method of
Cryptographic Message Syntax (CMS) as an additional algorithm for key management into the S/MIME Cryptographic Message Syntax [CMS] as
symmetric encryption. The relevant OIDs and processing steps are additional algorithms.
provided so that the AES algorithms may be included in the CMS
specification [CMS] for symmetric content and key encryption.
2. Conventions used in this document Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC-2119 [2]. this document are to be interpreted as described in RFC-2119 [2].
3. Overview 1. Overview
S/MIME (Secure/Multipurpose Internet Mail Extensions) [SMIME3] is a This document describes the conventions for using the RSAES-OAEP key
set of specifications for the secure transport of MIME objects. In transport algorithm and Advanced Encryption Standard (AES) content
encryption algorithm with the Cryptographic Message Syntax [CMS]
enveloped-data, encrypted-data and authenticated-data content types.
Schaad 1 While this document presents the use of the two algorithms together,
that fact does not imply that they cannot be used independently.
Schaad, Housley 1
Use of the AES Algorithm in CMS November 2000 Use of the AES Algorithm in CMS November 2000
the current (S/MIME v3) specifications the mandatory-to-implement They are presented together simply because the initial usage of each
symmetric algorithm for content encryption and key encryption is will be as a matched pair.
triple-DES (3DES). The algorithm is considered to be both more
secure and faster than 3DES.
AES is an iterated block cipher with a variable block length and a When the variant of the RSA key transport algorithm specified in PKCS
variable key length. In the base algorithm, the block length and the #1 Version 1.5 [PKCS#1v1.5] is used for key management, it is
key length can be independently specified to 128, 192 or 256 bits. vulnerable to adaptive chosen ciphertext attacks. This attack is
AES has fixed the block length to be 128-bits. explained in [RSALAB] and [CRYPTO98]. The use of PKCS #1 Version 1.5
key transport in interactive applications is especially vulnerable.
Exploitation of this identified vulnerability, revealing the result
of a particular RSA decryption, requires access to an oracle which
will respond to hundreds of thousands of ciphertexts, which are
constructed adaptively in response to previously-received replies
providing information on the successes or failures of attempted
decryption operations.
4. AES Algorithm The attack appears significantly less feasible in store-and-forward
environments, such as S/MIME. When PKCS #1 Version 1.5 key transport
is applied as an intermediate encryption layer within an interactive
request-response communications environment, exploitation could be
more feasible. However, Secure Sockets Layer (SSL) [SSL] and
Transport Layer Security (TLS) [TLS] protocol implementations could
include countermeasures that detect and prevent Bleichenbacher's and
other chosen-ciphertext attacks, without changing the way the RSA key
transport algorithm is used. These countermeasures are performed
within the protocol level. In the interest of long-term security
assurance, it is prudent to adopt an improved cryptographic technique
rather than embedding countermeasures within protocols.
AES is a symmetric block cipher with a block size of 128 bits and a An updated version of PKCS #1 has been published, PKCS #1 Version 2.0
key size of 128, 198 or 256-bits. AES is free of intellectual [PKCS#1v2.0]. This new document supersedes RFC 2313. PKCS #1
property issues. Compliant implementations MUST support key sizes of Version 2.0 preserves support for the encryption padding format
128 and 256 bits. Compliant implementation MAY support a key size of defined in PKCS #1 Version 1.5 [PKCS#1v1.5], and it also defines a
196 bits. Compliant implementations MUST support a block size of 128- new alternative. To resolve the adaptive chosen ciphertext
bits. vulnerability, the PKCS #1 Version 2.0 specifies and recommends use
of Optimal Asymmetric Encryption Padding (OAEP) when RSA encryption
is used to provide confidentiality, such as key transport.
4.1 Content Encryption This document specifies the use of RSAES-OAEP key transport algorithm
in the Cryptographic Message Syntax (CMS) [CMS]. CMS can be used in
either a store-and-forward or an interactive request-response
environment.
CMS supports variety of architectures for certificate-based key
management, particularly the one defined by the PKIX working group
[PROFILE]. PKCS #1 Version 1.5 and PKCS #1 Version 2.0 require the
same RSA public key information. Thus, a certified RSA public key
may be used with either RSA key transport technique.
CMS values are generated using ASN.1 [X.208-88], using the Basic
Encoding Rules (BER) [X.209-88] and the Distinguished Encoding Rules
(DER) [X.509-88].
2. Enveloped-data Conventions
Schaad, Housley 2
Use of the AES Algorithm in CMS November 2000
The CMS enveloped-data content type consists of encrypted content and
wrapped content-encryption keys for one or more recipients. The
RSAES-OAEP key transport algorithm is used to wrap the content-
encryption key for one recipient. The AES algorithm is used to
encrypt the content.
Compliant software MUST meet the requirements for constructing an
enveloped-data content type stated in [CMS] Section 6, "Enveloped-
data Content Type".
A content-encryption key MUST be randomly generated for each instance
of an enveloped-data content type. The content-encryption key is
used to encipher the content.
AES can be used with the enveloped-data content type using any of the
following key management techniques defined in [CMS] Section 6.
1) Key Transport: The AES CEK is uniquely wrapped for each recipient
using the recipient's public RSA key and other values. Section 2.XX
provides additional details. RSAES-OEAP is a key transport algorithm
and itĂs usage is described here.
2) Key Agreement: The AES CEK is uniquely wrapped for each recipient
using a pairwise symmetric key-encryption key (KEK) generated using
DH-ES using the a randomly generated private key value for the
originator, the recipient's public DH key and other values. Section
2.XX provides additional details.
3) "Previously Distributed" Symmetric KEK: The AES CEK is wrapped
using a "previously distributed" symmetric KEK (such as a Mail List
Key). The methods by which the symmetric KEK is generated and
distributed are beyond the scope of this document. Section 2.XXX
provides more details.
2.1 EnvelopedData Fields
The enveloped-data content type is ASN.1 encoded using the
EnvelopedData syntax. The fields of the EnvelopedData syntax must be
populated as follows:
The EnvelopedData version MUST be either 0 or 2.
The EnvelopedData originatorInfo field is not used for the RSAES-OAEP
key transport algorithm. However, this field MAY be present to
support recipients using other key management algorithms.
The EnvelopedData recipientInfos CHOICE is dependent on the key
managment technique used. Section 2.2, 2.3 and 2.4 provide more
inforamtion.
The EnvelopedData encryptedContentInfo contentEncryptionAlgorithm
field MUST specify a symmetric encryption algorithm. Implementations
MUST support the encryption of AES keys, but implementations MAY
support other algorithms as well.
Schaad, Housley 3
Use of the AES Algorithm in CMS November 2000
The EnvelopedData unprotectedAttrs MAY be present.
2.2 KeyTransRecipientInfo Fields
The enveloped-data content type is ASN.1 encoded using the
EnvelopedData syntax. The fields of the EnvelopedData syntax must be
populated as follows:
The KeyTransRecipientInfo version MUST be either 0 or 2. If the
RecipientIdentifier is the CHOICE issuerAndSerialNumber, then the
version MUST be 0. If the RecipientIdentifier is
subjectKeyIdentifier, then the version MUST be 2.
The KeyTransRecipientInfo RecipientIdentifier provides two
alternatives for specifying the recipient's certificate, and thereby
the recipient's public key. The recipient's certificate must contain
a RSA public key. The content-encryption key is encrypted with the
recipient's RSA public key. The issuerAndSerialNumber alternative
identifies the recipient's certificate by the issuer's distinguished
name and the certificate serial number; the subjectKeyIdentifier
identifies the recipient's certificate by the X.509
subjectKeyIdentifier extension value.
The KeyTransRecipientInfo keyEncryptionAlgorithm specifies that the
RSAES-OAEP algorithm, and its associated parameters, was used to
encrypt the content-encryption key for the recipient. The key-
encryption process is described in [PKCS#1v2.0]. See section 3 of
this document for the algorithm identifier and the parameter syntax.
The KeyTransRecipientInfo encryptedKey is the result of encrypting
the content-encryption key in the recipient's RSA public key using
the RSAES-OAEP algorithm. When using a Triple-DES content-encryption
key, implementations MUST adjust the parity bits for each DES key
comprising the Triple-DES key prior to RSAES-OAEP encryption.
2.3 KeyAgreeRecipientInfo Fields
This section describes the conventions for using ES-DH and AES with
the CMS enveloped-data content type to support key agreement. When
key agreement is used, then the RecipientInfo keyAgreeRecipientInfo
CHOICE MUST be used.
The KeyAgreeRecipient version MUST be 3.
The EnvelopedData originatorInfo field must be the originatorKey
alternative. The originatoryKey algorithm fields MUST contain the
dh-public-number object identifier with absent parameters. The
originatorKey publicKey MUST contain the senderĂs ephemeral public
key.
The EnvelopedData ukm MAY be absent.
Schaad, Housley 4
Use of the AES Algorithm in CMS November 2000
The EnvelopedData keyEncrytionAlgorithm MUST be the id-alg-ESDH
algorithm identifier.
2.3.1 ES-DH/AES Key Derivation
Generation of the an AES key used in doing AES-KeyWrap is done using
the method in [DH] with the following modifications:
The Hash function H will be [SHA-256] rather than SHA-1.
NOTE: 2 examples to be provided at this location.
2.3.2 AES CEK Wrap Process
To be supplied.
2.4 KEKRecipientInfo Fields
This section describes the conventions for using AES with the CMS
enveloped-data content type to support "previously distributed"
symmetric KEKs. When a "previously distributed" symmetric KEK is
used to wrap the AES CEK, then the RecipientInfo KEKRecipientInfo
CHOICE MUST be used. The methods used to generate and distribute the
symmetric KEK are beyond the scope of this document.
The KEKRecipientInfo fields MUST be populated as specified in [CMS]
Section 6.2.3, "KEKRecipientInfo Type". The KEKRecipientInfo
keyEncryptionAlgorithm algorithm field MUST be the id-NIST-AES-KEY-
WRAP OID indicating that the AES wrap function is used to wrap the
AES CEK. The KEKRecipientInfo keyEncryptionAlgorithm parameters field
MUST be absent. The KEKRecipientInfo encryptedKey field MUST include
the AES CEK wrapped using the "previously distributed" symmetric KEK
as input to the AES wrap function.
To Be Decided ű Do we have multiple sizes of key wrap algorithms.
3. Encrypted-data Conventions
To be supplied.
4. Authenticated-data Conventions
To be supplied.
5. Algorithm Identifiers and Parameters
5.1 RSAES-OAEP Algorithm Identifiers and Parameters
The RSAES-OAEP key transport algorithm is the RSA encryption scheme
defined in RFC 2437 [PKCS#1v2.0], where the message to be encrypted
is the content-encryption key. The algorithm identifier for RSAES-
OAEP is:
id-RSAES-OAEP OBJECT IDENTIFIER ::=
Schaad, Housley 5
Use of the AES Algorithm in CMS November 2000
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1)
7 }
The AlgorithmIdentifier parameters field must be present, and the
parameters field must contain RSAES-OAEP-params. RSAES-OAEP-params
have the following syntax:
RSAES-OAEP-params ::= SEQUENCE
hashFunc [0] AlgorithmIdentifier DEFAULT sha1Identifier,
maskGenFunc [1] AlgorithmIdentifier DEFAULT mgf1SHA1Identifier,
pSourceFunc [2] AlgorithmIdentifier DEFAULT
pSpecifiedEmptyIdentifier }
sha1Identifier ::= AlgorithmIdentifier
id-sha1, NULL }
mgf1SHA1Identifier ::= AlgorithmIdentifier
id-mgf1, sha1Identifier }
pSpecifiedEmptyIdentifier ::= AlgorithmIdentifier
id-pSpecified, OCTET STRING SIZE (0) }
id-sha1 OBJECT IDENTIFIER ::=
iso(1) identified-organization(3) oiw(14) secsig(3)
algorithms(2) 26 }
id-mgf1 OBJECT IDENTIFIER ::=
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1)
8 }
id-pSpecified OBJECT IDENTIFIER ::=
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1)
9 }
The fields of type RSAES-OAEP-params have the following meanings:
hashFunc identifies the one-way hash function. Implementations
MUST support SHA-1 [SHA1]. The SHA-1 algorithm identifier is
comprised of the id-sha1 object identifier and a parameter of NULL.
Implementations that perform encryption MUST omit the hashFunc field
when SHA-1 is used, indicating that the default algorithm was used.
Implementations that perform decryption MUST recognize both the id-
sha1 object identifier and an absent hashFunc field as an indication
that SHA-1 was used.
maskGenFunc identifies the mask generation function.
Implementations MUST support MFG1 [PKCS#1v2.0]. MFG1 requires a one-
way hash function, and it is identified in the parameter field of the
MFG1 algorithm identifier. Implementations MUST support SHA-1
[SHA1]. The MFG1 algorithm identifier is comprised of the id-mgf1
object identifier and a parameter that contains the algorithm
identifier of the one-way hash function employed with MFG1. The SHA-
1 algorithm identifier is comprised of the id-sha1 object identifier
and a parameter of NULL. Implementations that perform encryption
Schaad, Housley 6
Use of the AES Algorithm in CMS November 2000
MUST omit the maskGenFunc field when MFG1 with SHA-1 is used,
indicating that the default algorithm was used. Implementations that
perform decryption MUST recognize both the id-mgf1 and id-sha1 object
identifiers as well as an absent maskGenFunc field as an indication
that MFG1 with SHA-1 was used.
pSourceFunc identifies the source (and possibly the value) of the
encoding parameters, commonly called P. Implementations MUST
represent P by an algorithm identifier, id-pSpecified, indicating
that P is explicitly provided as an OCTET STRING in the parameters.
The default value for P is an empty string. In this case, pHash in
EME-OAEP contains the hash of a zero length string. Implementations
MUST support a zero length P value. Implementations that perform
encryption MUST omit the pSourceFunc field when a zero length P value
is used, indicating that the default value was used. Implementations
that perform decryption MUST recognize both the id-pSpecified object
identifier and an absent pSourceFunc field as an indication that a
zero length P value was used.
5.2 AES Algorithm Identifiers and Parameters
AES is added to the set of symmetric content encryption algorithms in AES is added to the set of symmetric content encryption algorithms in
CMS. The AES content-encryption algorithm in Cipher Block Chaining CMS. The AES content-encryption algorithm in Cipher Block Chaining
(CBC) mode for the three different key sizes are identified by the (CBC) mode for the three different key sizes are identified by the
OID: OID:
id-aes128-CBC OBJECT IDENTIFIER ::= { aes 2 } id-aes128-CBC OBJECT IDENTIFIER ::= { aes 2 }
id-aes192-CBC OBJECT IDENTIFIER ::= { aes 22 } id-aes192-CBC OBJECT IDENTIFIER ::= { aes 22 }
id-aes256-CBC OBJECT IDENTIFIER ::= { aes 42 } id-aes256-CBC OBJECT IDENTIFIER ::= { aes 42 }
The AlgorithmIdentifier parameters field MUST be present, and the The AlgorithmIdentifier parameters field MUST be present, and the
parameters field MUST contain a AES-IV associated with this OID parameters field MUST contain a AES-IV associated with this OID
contains the initialization vector IV: contains the initialization vector IV:
AES-IV ::= OCTET STRING (SIZE(16)) AES-IV ::= OCTET STRING (SIZE(16))
4.2 Key Wrap 6 SMIMECapabilities Attribute Conventions
NOTE: This section is subject to change when the key wrap algorithm An S/MIME client SHOULD announce the set of cryptographic functions
(see section 5) is selected. it supports by using the S/MIME capabilities attribute. This
attribute provides a partial list of OIDs of cryptographic functions
and MUST be signed by the client. The algorithm OIDs SHOULD be
logically separated in functional categories and MUST be ordered with
respect to their preference.
AES key wrap has the algorithm identifier: RFC 2633, Section 2.5.2 defines the SMIMECapabilities signed
attribute (defined as a SEQUENCE of SMIMECapability SEQUENCEs) to be
used to specify a partial list of algorithms that the software
announcing the SMIMECapabilities can support.
id-xxxxx-AESWrap ::= {TBD} 6.1 RSAES-OEAP SMIMECapability Attribute
The algorithm identifier parameter field MUST be present, and the Schaad, Housley 7
parameter field MUST contain a AESCBCWrap object: Use of the AES Algorithm in CMS November 2000
AESCBCWrap ::= NULL When constructing a signedData object, compliant software MAY include
the SMIMECapabilities signed attribute announcing that it supports
the RSAES-OAEP algorithm.
The key wrap algorithm used to encrypt an AES content-encryption key The SMIMECapability SEQUENCE representing RSAES-OAEP MUST include the
with a AES key-encryption key is specified in section 2. id-RSAES-OAEP object identifier in the capabilityID field and MUST
include the RSAES-OAEP-Default-Identifier SEQUENCE in the parameters
field.
Schaad 2 RSAES-OAEP-Default-Identifier ::= AlgorithmIdentifier
Use of the AES Algorithm in CMS November 2000
Out-of-band distribution of the AES key-encryption key used to id-RSAES-OAEP,
encrypt the AES content-encryption key is beyond of the scope of this
document.
The key encryption key used with the wrapping algorithm MUST be 256- sha1Identifier, mgf1SHA1Identifier, pSpecifiedEmptyIdentifier
bits. } }
4.3 S/MIME Capability Attribute When all of the default settings are selected, the SMIMECapability
SEQUENCE representing RSAES-OAEP MUST be DER-encoded as:
An S/MIME client SHOULD announce the set of cryptographic functions 30 0D 06 09 2A 86 48 86 F7 0D 01 01 07 30 00
it supports by using the S/MIME capabilities attribute. This
attribute provides a partial list of OIDs of cryptographic functions
and MUST be signed by the client. The algorithm OIDs SHOULD be
logically separated in functional categories and MUST be ordered with
respect to their preference. If an S/MIME client is required to
support symmetric encryption with AES, the capabilities attribute
MUST contain the AES OID specified above in the category of symmetric
algorithms. The parameter associated with this OID MUST is
AESSMimeCapability.
AESSMimeCapabilty ::= SEQUENCE 6.2 AES S/MIME Capability Attributes
KeySize INTEGER If an S/MIME client is required to support symmetric encryption with
} AES, the capabilities attribute MUST contain the AES OID specified
above in the category of symmetric algorithms. The parameter
associated with this OID MUST is AESSMimeCapability.
AESSMimeCapabilty ::= NULL
The encodings for the mandatory key sizes are: The encodings for the mandatory key sizes are:
Key Size Capability Key Size Capability
128 30 XX 06 XX YY YY YY 30 04 02 02 00 80 128 30 0D 06 09 60 86 48 01 65 03 04 01 02 30 00
196 30 XX 06 XX YY YY YY 30 04 02 02 00 C0 196 30 0D 06 09 60 86 48 01 65 03 04 01 16 30 00
256 30 XX 06 XX YY YY YY 30 04 02 02 01 00 256 30 0D 06 09 60 86 48 01 65 03 04 01 2A 30 00
When a sending agent creates an encrypted message, it has to decide When a sending agent creates an encrypted message, it has to decide
which type of encryption algorithm to use. In general the decision which type of encryption algorithm to use. In general the decision
process involves information obtained from the capabilities lists process involves information obtained from the capabilities lists
included in messages received from the recipient, as well as other included in messages received from the recipient, as well as other
information such as private agreements, user preferences, legal information such as private agreements, user preferences, legal
restrictions, and so on. If users require AES for symmetric restrictions, and so on. If users require AES for symmetric
encryption, the S/MIME clients on both the sending and receiving side encryption, the S/MIME clients on both the sending and receiving side
MUST support it, and it MUST be set in the user preferences. MUST support it, and it MUST be set in the user preferences.
5. AES Key Wrap Algorithm 7. Security Considerations
NOTE: Although no key wrap algorithms have been announced by NIST, a
request has been submitted that they designate a key wrap algorithm
as part of the AES standard. In the event that this is done, this
entire section is to be replaced with the NIST designated algorithm.
Should NIST decide not to provide a key wrap algorithm, it is
expected we will develop one based on the current CMS key wrap
algorithm.
6. Key Management for AES Note on mix of OEAP and v1.5 RSA encryption from RFC 2437
Schaad 3 Implementations must protect the RSA private key and the content-
encryption key. Compromise of the RSA private key may result in the
disclosure of all messages protected with that key. Compromise of
the content-encryption key may result in disclosure of the associated
encrypted content.
Schaad, Housley 8
Use of the AES Algorithm in CMS November 2000 Use of the AES Algorithm in CMS November 2000
CMS accommodates three general key management techniques: key Implementations must protect the key management private key and the
transport, key agreement, and previously distributed symmetric key- message-authentication key. Compromise of the key management private
encryption keys. key permits masquerade of authenticated data. Compromise of the
message-authentication key may result in undetectable modification of
6.1 Key Transport for AES the authenticated content.
Key Transport using RSA-OEAP MUST be implemented to comply with this
document.
Key transport algorithm identifiers are located in the EnvelopedData The generation of RSA public/private key pairs relies on a random
RecipientInfos KeyTransRecipientInfo keyEncryptionAlgorithm and numbers. The use of inadequate pseudo-random number generators
AuthenticatedData RecipientInfos KeyTransRecipientInfo (PRNGs) to generate cryptographic keys can result in little or no
keyEncryptionAlgorithm fields. security. An attacker may find it much easier to reproduce the PRNG
environment that produced the keys, searching the resulting small set
of possibilities, rather than brute force searching the whole key
space. The generation of quality random numbers is difficult. RFC
1750 [RANDOM] offers important guidance in this area.
Key transport encrypted content-encryption keys are located in the 8. Open Issues
EnvelopedData RecipientInfos KeyTransRecipientInfo encryptedKey
field. Key transport encrypted message-authentication keys are
located in the AuthenticatedData RecipientInfos KeyTransRecipientInfo
encryptedKey field.
6.2 Key Agreement for AES - Key wrap algorithm is undetermined.
- Mandatory key sizes for Key Wrap
- Mandatory key sizes for AES algorithm
- Supplying any patent and licensing statements.
- References to each algorithm that would be acceptable to the RFC
editor.
- Does the oid for key derivation need to be changed since we are
using SHA-256 not SHA-1?
Implementations MAY include key agreement using X9.42 Ephemeral- References
Static Diffie-Hellman. If ESDH is implemented, AES-KeyWrap MUST be
implemented.
A CMS implementation may support mixed key-encryption and content- CMS Housley, R. Cryptographic Message Syntax. RFC 2630.
encryption algorithms. For example, a 128-bit AES content-encryption June 1999.
key may be wrapped with 168-bit Triple DES key-encryption key.
Similarly, a 128-bit AES content-encryption key may be wrapped with
256-bit AES key-encryption key.
Key agreement algorithm identifiers are located in the EnvelopedData CRYPTO98 Bleichenbacher, D. "Chosen Ciphertext Attacks Against
RecipientInfos KeyAgreeRecipientInfo keyEncryptionAlgorithm and Protocols Based on the RSA Encryption Standard PKCS #1,"
AuthenticatedData RecipientInfos KeyAgreeRecipientInfo in H. Krawczyk (editor), Advances in Cryptology - CRYPTO
keyEncryptionAlgorithm fields. '98
Proceedings, Lecture Notes in Computer Science 1462
(1998),
Springer-Verlag, pp. 1-12.
Key wrap algorithm identifiers are located in the KeyWrapAlgorithm DH E. Rescorla, ˘Diffie-Hellman Key Agreement Method÷, RFC
parameters within the EnvelopedData RecipientInfos 2631, June 1999.
KeyAgreeRecipientInfo keyEncryptionAlgorithm and AuthenticatedData
RecipientInfos KeyAgreeRecipientInfo keyEncryptionAlgorithm fields.
Wrapped content-encryption keys are located in the EnvelopedData MUSTSHOULD Bradner, S. Key Words for Use in RFCs to Indicate
RecipientInfos KeyAgreeRecipientInfo RecipientEncryptedKeys Requirement Levels. BCP 14, RFC 2119. March 1997.
encryptedKey field. Wrapped message-authentication keys are located
in the AuthenticatedData RecipientInfos KeyAgreeRecipientInfo
RecipientEncryptedKeys encryptedKey field.
Diffie-Hellman Key Wrap Key Derivation PKCS#1v1.5 Kaliski, B. PKCS #1: RSA Encryption, Version 1.5.
RFC 2313. March 1998.
Generation of the an AES key used in doing AES-KeyWrap is done using PKCS#1v2.0 Kaliski, B. PKCS #1: RSA Encryption, Version 2.0.
the method in [DH] with the following modifications: RFC 2437. October 1998.
Schaad 4 PROFILE Housley, R., W. Ford, W. Polk, and D. Solo. Internet
Schaad, Housley 9
Use of the AES Algorithm in CMS November 2000 Use of the AES Algorithm in CMS November 2000
The Hash function H will be [SHA-256] rather than SHA-1. X.509 Public Key Infrastructure: Certificate and CRL
Profile. RFC 2459. January 1999.
NOTE: 2 examples to be provided at this location.
6.3 Symmetric Key-Encryption Key Algorithms with AES
CMS implementations MAY include symmetric key-encryption key
management. Implementations compliant with this document MUST
include AES-256 key-encryption keys wrapping AES content-encryption
keys. A CMS implementation may support mixed key-encryption and
content-encryption algorithms. For example, a 128-bit AES content-
encryption key may be wrapped with 168-bit Triple-DES key-encryption
key or with a 256-bit AES key-encryption key.
Key wrap algorithm identifiers are located in the EnvelopedData
RecipientInfos KEKRecipientInfo keyEncryptionAlgorithm and
AuthenticatedData RecipientInfos KEKRecipientInfo
keyEncryptionAlgorithm fields.
Wrapped content-encryption keys are located in the EnvelopedData
RecipientInfos KEKRecipientInfo encryptedKey field. Wrapped message-
authentication keys are located in the AuthenticatedData
RecipientInfos KEKRecipientInfo encryptedKey field.
The output of a key agreement algorithm is a key-encryption key, and RANDOM Eastlake, D., S. Crocker, and J. Schiller. Randomness
this key-encryption key is used to encrypt the content-encryption Recommendations for Security. RFC 1750. December 1994.
key. In conjunction with key agreement algorithms, CMS
implementations must include encryption of content-encryption keys
with the pairwise key-encryption key generated using a key agreement
algorithm. To support key agreement, key wrap algorithm identifiers
are located in the KeyWrapAlgorithm parameter of the EnvelopedData
RecipientInfos KeyAgreeRecipientInfo keyEncryptionAlgorithm and
AuthenticatedData RecipientInfos KeyAgreeRecipientInfo
keyEncryptionAlgorithm fields. Wrapped content-encryption keys are
located in the EnvelopedData RecipientInfos KeyAgreeRecipientInfo
RecipientEncryptedKeys encryptedKey field, wrapped message-
authentication keys are located in the AuthenticatedData
RecipientInfos KeyAgreeRecipientInfo RecipientEncryptedKeys
encryptedKey field.
7. Security Considerations RSALABS Bleichenbacher, D., B. Kaliski, and J. Staddon.
Recent Results on PKCS #1: RSA Encryption Standard.
RSA Laboratories' Bulletin No. 7, June 26, 1998.
[Available at
http://www.rsasecurity.com/rsalabs/bulletins]
To be supplied SHA1 National Institute of Standards and Technology.
FIPS Pub 180-1: Secure Hash Standard. 17 April 1995.
Note on mix of OEAP and v1.5 RSA encryption from RFC 2437 SSL Freier, A., P. Karlton, and P. Kocher. The SSL
Protocol,
Version 3.0. Netscape Communications. November 1996.
[Available at http://draft-freier-ssl-version3-02.txt]
8. Open Issues TLS Dierks, T. and C. Allen. The TLS Protocol Version 1.0.
RFC 2246. January 1999.
- Key wrap algorithm is undetermined. X.208-88 CCITT. Recommendation X.208: Specification of Abstract
- Mandatory key sizes for Key Wrap Syntax Notation One (ASN.1). 1988.
- Mandatory key sizes for AES algorithm
- Supplying any patent and licensing statements.
Schaad 5 X.209-88 CCITT. Recommendation X.209: Specification of Basic
Use of the AES Algorithm in CMS November 2000 Encoding
Rules for Abstract Syntax Notation One (ASN.1). 1988.
- References to each algorithm that would be acceptable to the RFC X.509-88 CCITT. Recommendation X.509: The Directory -
editor. Authentication
Framework. 1988.
References Acknowledgements
[DH] E. Rescorla, ˘Diffie-Hellman Key Agreement Method÷, RFC 2631, This document is the result of contributions from many
June 1999. professionals. We appreciate the hard work of all members of the
IETF S/MIME Working Group. We wish to extend a special thanks to
Burt Kaliski.
[IPR] See the "IETF Page of Intellectual Property Rights Notices", Author's Addresses
http://www.ietf.cnri.reston.va.us/ipr.html
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate Requirement Jim Schaad
Levels", Internet Request for Comments RFC 2119, March 1997. Soaring Hawk Consulting
Email: jimsch@exmsft.com
[CMS] R. Housley, "Cryptographic Message Syntax", Internet Request for Russell Housley
Comments RFC 2630, June 1999. RSA Laboratories
918 Spring Knoll Drive
Herndon, VA 20170
USA
[RSA-OEAP] R. Housley, ˘Use of the RSAES-OEAP Key Transport Algorithm in Schaad, Housley 10
CMS÷, draft-ietf-smime-cms-rsaes-oeap.txt, June 2000. Use of the AES Algorithm in CMS November 2000
[SMIME3] B. Ramsdell, "S/MIME Version 3 Certificate Handling", Internet rhousley@rsasecurity.com
Request for Comments RFC 2632, June 1999.
B. Ramsdell, "S/MIME Version 3 Message Specification",
Internet Request for Comments RFC 2633, June 1999.
11. Author's Addresses 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
Jim Schaad 2 Bradner, S., "Key words for use in RFCs to Indicate Requirement
Soaring Hawk Consulting Levels", BCP 14, RFC 2119, March 1997
Email: jimsch@exmsft.com
Schaad 6 Schaad, Housley 11
 End of changes. 

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