draft-ietf-smime-pss-02.txt   draft-ietf-smime-pss-03.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-pss-02.txt November 2003 Document: draft-ietf-smime-pss-03.txt December 2003
Category: Standards Category: Standards
Use of the RSA PSS Signature Algorithm in CMS Use of the RSA PSS Signature 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].
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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[STDWORDS]. [STDWORDS].
1. Overview 1. Overview
This document specifies the conventions for using the RSASSA-PSS (RSA This document specifies the conventions for using the RSASSA-PSS (RSA
Signature Scheme with Appendix - Probabilistic Signature Scheme) Signature Scheme with Appendix - Probabilistic Signature Scheme)
[P1v2.1] digital signature algorithm with the Cryptographic Message [P1v2.1] digital signature algorithm with the Cryptographic Message
Syntax [CMS] signed-data content type. Syntax [CMS] signed-data content type.
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CMS values are generated using ASN.1 [X.208-88], using the Basic CMS values are generated using ASN.1 [X.208-88], using the Basic
Encoding Rules (BER) [X.209-88] and the Distinguished Encoding Rules Encoding Rules (BER) [X.209-88] and the Distinguished Encoding Rules
(DER) [X.509-88]. (DER) [X.509-88].
This document is written to be used in conjunction with RFC XXX [RSA-
ALGS]. All of the ASN.1 structures referenced in this document are
defined in RFC XXX.
1.1 PSS Algorithm 1.1 PSS Algorithm
Although there are no known defects with the PKCS #1 v1.5 [P1v1.5] Although there are no known defects with the PKCS #1 v1.5 [P1v1.5]
signature algorithm, RSASSA-PSS [P1v2.1] was developed in an effort signature algorithm, RSASSA-PSS [P1v2.1] was developed in an effort
to have more mathematically provable security. PKCS #1 v1.5 to have more mathematically provable security. PKCS #1 v1.5
signatures were developed in an ad hoc manner, RSASSA-PSS was signatures were developed in an ad hoc manner, RSASSA-PSS was
developed based on mathematical foundations. developed based on mathematical foundations.
2. Algorithm Identifiers and Parameters 2. Algorithm Identifiers and Parameters
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and a public exponent, MUST be encoded using the RSAPublicKey type. and a public exponent, MUST be encoded using the RSAPublicKey type.
The output of this encoding is carried in the certificate subject The output of this encoding is carried in the certificate subject
public key. public key.
RSAPublicKey ::= SEQUENCE { RSAPublicKey ::= SEQUENCE {
modulus INTEGER, -- n modulus INTEGER, -- n
publicExponent INTEGER } -- e publicExponent INTEGER } -- e
2.2 Signature Identifiers 2.2 Signature Identifiers
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The algorithm identifier for RSASAA-PSS signatures is: The algorithm identifier for RSASAA-PSS signatures is:
id-RSASSA-PSS OBJECT IDENTIFER ::= {pkcs-1 10 } id-RSASSA-PSS OBJECT IDENTIFER ::= {pkcs-1 10 }
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When the id-RSASSA-PSS algorithm identifier is used for a signature, When the id-RSASSA-PSS algorithm identifier is used for a signature,
the AlgorithmIdentifier parameters field MUST contain RSASSA-PSS- the AlgorithmIdentifier parameters field MUST contain RSASSA-PSS-
params. Information about RSASSA-PSS-params can be found in [RSA- params. Information about RSASSA-PSS-params can be found in [RSA-
ALGS]. ALGS].
When signing, the RSA algorithm generates a single value, and that When signing, the RSA algorithm generates a single value, and that
value is used directly as the signature value. value is used directly as the signature value.
3. Signed-data Conventions 3. Signed-data Conventions
digestAlgorithms SHOULD contain the one-way hash function used to digestAlgorithms SHOULD contain the one-way hash function used to
compute the message digest on the eContent value. compute the message digest on the eContent value.
The same one-way hash function SHOULD be used for computing the The same one-way hash function SHOULD be used for computing the
message digest on both the eContent and the signedAttributes value message digest on both the eContent and the signedAttributes value
if signedAttributes exist. if signedAttributes exist.
The same one-way hash function SHOULD be used for computing the The same one-way hash function MUST be used for computing the
message digest on the signedAttributes and as the hashAlgorithm in message digest on the signedAttributes and as the hashAlgorithm in
the RSA-PSS-params structure. the RSA-PSS-params structure.
signatureAlgorithm MUST contain id-RSASSA-PSS. The algorithm signatureAlgorithm MUST contain id-RSASSA-PSS. The algorithm
parameters field MUST contain RSASSA-PSS-params. parameters field MUST contain RSASSA-PSS-params.
signature contains the single value resulting from the signing signature contains the single value resulting from the signing
operation. operation.
If the subjectPublicKeyInfo algorithm identifier for the public key If the subjectPublicKeyInfo algorithm identifier for the public key
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3. The saltLength in the signatureAlgorithm parameters MUST be 3. The saltLength in the signatureAlgorithm parameters MUST be
greater or equal to the saltLength in the certificate greater or equal to the saltLength in the certificate
subjectPublicKey.algorithm parameters. subjectPublicKey.algorithm parameters.
4. The trailerField in the certificate subjectPublicKey.algorithm 4. The trailerField in the certificate subjectPublicKey.algorithm
parameters and signatureAlgorithm parameters MUST be the same. parameters and signatureAlgorithm parameters MUST be the same.
In doing the above comparisons, default values are considered to be In doing the above comparisons, default values are considered to be
the same as extant values. If any of the above four steps is not the same as extant values. If any of the above four steps is not
true, the signature checking algorithm MUST fail validation. true, the signature checking algorithm MUST fail validation.
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Schaad Standards - Exp: August 2003 3 4. Security Considerations
CMS and PSS Signature February 2003
Implementations must protect the RSA private key. Compromise of the Implementations must protect the RSA private key. Compromise of the
RSA private key may result in the ability to forge signatures. RSA private key may result in the ability to forge signatures.
The generation of RSA private key relies on random numbers. The use The generation of RSA private key relies on random numbers. The use
of inadequate pseudo-random number generators (PRNGs) to generate of inadequate pseudo-random number generators (PRNGs) to generate
these values can result in little or no security. An attacker may these values can result in little or no security. An attacker may
find it much easier to reproduce the PRNG environment that produced find it much easier to reproduce the PRNG environment that produced
the keys, searching the resulting small set of possibilities, rather the keys, searching the resulting small set of possibilities, rather
than brute force searching the whole key space. The generation of than brute force searching the whole key space. The generation of
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of allowing an attacker to get extra information about the key. It of allowing an attacker to get extra information about the key. It
is strongly suggested that the same key not be used for both the PKCS is strongly suggested that the same key not be used for both the PKCS
#1 v1.5 and RSASSA-PSS signature algorithms. #1 v1.5 and RSASSA-PSS signature algorithms.
When computing signatures, the same hash function should be used for When computing signatures, the same hash function should be used for
all operations. This reduces the number of failure points in the all operations. This reduces the number of failure points in the
signature process. signature process.
The parameter checking procedures outlined in section 3 are of
special importance. It is possible to forge signatures by changing
(especially to weaker values) these parameter values. Signers using
this algorithm should take care that only one set of parameter values
is used as this decreases the possibility of leaking information.
5. Normative References 5. Normative References
CMS Housley, R, "Cryptographic Message Syntax", CMS Housley, R, "Cryptographic Message Syntax",
RFC 3369, August 2002. RFC 3369, August 2002.
P1v2.1 Jonsson, J., and B. Kaliski, "PKCS #1: RSA P1v2.1 Jonsson, J., and B. Kaliski, "PKCS #1: RSA
Cryptography Specification Version 2.1", Cryptography Specification Version 2.1",
RFC 3447, February 2003. RFC 3447, February 2003.
RSA-ALGS Schaad, J., B. Kaliski and R Housley, "Additional RSA-ALGS Schaad, J., B. Kaliski and R Housley, "Additional
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draft-ietf-pkix-rsa-pkalgs-01.txt, draft-ietf-pkix-rsa-pkalgs-01.txt,
November 2003. November 2003.
STDWORDS S. Bradner, "Key Words for Use in RFCs to STDWORDS S. Bradner, "Key Words for Use in RFCs to
Indicate Requirement Levels", RFC 2119, March Indicate Requirement Levels", RFC 2119, March
1997. 1997.
X.208-88 CCITT Recommendation X.208: Specification of X.208-88 CCITT Recommendation X.208: Specification of
Abstract Syntax Notation One (ASN.1), 1998. Abstract Syntax Notation One (ASN.1), 1998.
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X.209-88 CCITT Recommendation X.209: Specification of X.209-88 CCITT Recommendation X.209: Specification of
Basic Encoding Rules for Abstract Syntax Basic Encoding Rules for Abstract Syntax
Notation One (ASN.1), 1988. Notation One (ASN.1), 1988.
X.509-88 CCITT Recommendation X.509: The Directory X.509-88 CCITT Recommendation X.509: The Directory
Authentication Framework, 1988. Authentication Framework, 1988.
6. Informational References 6. Informational References
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CMS and PSS Signature February 2003
P1v1.5 Kaliski, B. and J. Staddon, "PKCS #1: RSA Encryption, P1v1.5 Kaliski, B. and J. Staddon, "PKCS #1: RSA Encryption,
Version 2.0, RFC 2437, October 1998. Version 2.0, RFC 2437, October 1998.
PKALGS Polk, W, R Housley, L. Bassham, "Algorithms and Identifiers PKALGS Polk, W, R Housley, L. Bassham, "Algorithms and Identifiers
for the Internet X.509 Public Key Infrastructure for the Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile", Certificate and Certificate Revocation List (CRL) Profile",
RFC 3279, April 2002. RFC 3279, April 2002.
RANDOM Eastlake, D., S. Crocker and J. Schiller RANDOM Eastlake, D., S. Crocker and J. Schiller
"Randomness Recommendations for Security", "Randomness Recommendations for Security",
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the copyright notice or references to the Internet Society or other the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than followed, or as required to translate it into languages other than
English. English.
The limited permissions granted above are perpetual and will not be The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. revoked by the Internet Society or its successors or assigns.
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