draft-ietf-lamps-cms-update-alg-id-protect-03.txt   draft-ietf-lamps-cms-update-alg-id-protect-04.txt 
Network Working Group R. Housley Network Working Group R. Housley
Internet-Draft Vigil Security Internet-Draft Vigil Security
Updates: 5652 (if approved) August 07, 2020 Updates: 5652 (if approved) August 27, 2020
Intended status: Standards Track Intended status: Standards Track
Expires: February 8, 2021 Expires: February 28, 2021
Update to the Cryptographic Message Syntax (CMS) for Algorithm Update to the Cryptographic Message Syntax (CMS) for Algorithm
Identifier Protection Identifier Protection
draft-ietf-lamps-cms-update-alg-id-protect-03 draft-ietf-lamps-cms-update-alg-id-protect-04
Abstract Abstract
This document updates the Cryptographic Message Syntax (CMS) This document updates the Cryptographic Message Syntax (CMS)
specified in RFC 5652 to ensure that algorithm identifiers in signed- specified in RFC 5652 to ensure that algorithm identifiers in signed-
data and authenticated-data content types are adequately protected. data and authenticated-data content types are adequately protected.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 8, 2021. This Internet-Draft will expire on February 28, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Required use the same hash algorithm . . . . . . . . . . . . 3 3. Required use the same hash algorithm . . . . . . . . . . . . 3
3.1. RFC 5652, Section 5.3 . . . . . . . . . . . . . . . . . . 3 3.1. RFC 5652, Section 5.3 . . . . . . . . . . . . . . . . . . 3
3.2. RFC 5652, Section 5.4 . . . . . . . . . . . . . . . . . . 4 3.2. RFC 5652, Section 5.4 . . . . . . . . . . . . . . . . . . 4
3.3. RFC 5652, Section 5.6 . . . . . . . . . . . . . . . . . . 4 3.3. RFC 5652, Section 5.6 . . . . . . . . . . . . . . . . . . 4
3.4. Backward Compatibility Considerations . . . . . . . . . . 5 3.4. Backward Compatibility Considerations . . . . . . . . . . 5
3.5. Timestamp Compatibility Considerations . . . . . . . . . 5 3.5. Timestamp Compatibility Considerations . . . . . . . . . 5
4. Recommend inclusion of the CMSAlgorithmProtection attribute . 5 4. Recommended inclusion of the CMSAlgorithmProtection attribute 6
4.1. RFC 5652, Section 14 . . . . . . . . . . . . . . . . . . 6 4.1. RFC 5652, Section 14 . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
This document updates the Cryptographic Message Syntax (CMS) This document updates the Cryptographic Message Syntax (CMS)
[RFC5652] to ensure that algorithm identifiers in signed-data and [RFC5652] to ensure that algorithm identifiers in signed-data and
authenticated-data content types are adequately protected. authenticated-data content types are adequately protected.
The CMS signed-data Content Type [RFC5652], unlike X.509 certificates The CMS signed-data Content Type [RFC5652], unlike X.509 certificates
[RFC5280], can be vulnerable to algorithm substitution attacks. In [RFC5280], can be vulnerable to algorithm substitution attacks. In
an algorithm substitution attack, the attacker changes either the an algorithm substitution attack, the attacker changes either the
algorithm identifier or the parameters associated with the algorithm algorithm identifier or the parameters associated with the algorithm
identifier to change the verification process used by the recipient. identifier to change the verification process used by the recipient.
The X.509 certificate structure protects the algorithm identifier and The X.509 certificate structure protects the algorithm identifier and
the associate parameters by signing them. the associated parameters by signing them.
In an algorithm substitution attack, the attacker looks for a In an algorithm substitution attack, the attacker looks for a
different algorithm that produces the same result as the algorithm different algorithm that produces the same result as the algorithm
used by the originator. As an example, if the signer of a message used by the originator. As an example, if the signer of a message
used SHA-256 [SHS] as the digest algorithm to hash the message used SHA-256 [SHS] as the digest algorithm to hash the message
content, then the attacker looks for a weaker hash algorithm that content, then the attacker looks for a weaker hash algorithm that
produces a result that is of the same length. The attacker's goal is produces a result that is of the same length. The attacker's goal is
to find a different message that results in the same hash value, to find a different message that results in the same hash value,
which is commonly called a collision. Today, there are many hash which is called a cross-algorithm collision. Today, there are many
functions that produce 256-bit results. One of them may be found to hash functions that produce 256-bit results. One of them may be
be weak in the future. found to be weak in the future.
Further, when a digest algorithm produces a larger result than is Further, when a digest algorithm produces a larger result than is
needed by a digital signature algorithm, the digest value is reduced needed by a digital signature algorithm, the digest value is reduced
to the size needed by the signature algorithm. This can be done both to the size needed by the signature algorithm. This can be done both
by truncation and modulo operations, with the simplest being by truncation and modulo operations, with the simplest being
straightforward truncation. In this situation, the attacker needs to straightforward truncation. In this situation, the attacker needs to
find a collision with the reduced digest value. As an example, if find a collision with the reduced digest value. As an example, if
the message signer uses SHA-512 [SHS] as the digest algorithm and the message signer uses SHA-512 [SHS] as the digest algorithm and
ECDSA with the P-256 curve [DSS] as the signature algorithm, then the ECDSA with the P-256 curve [DSS] as the signature algorithm, then the
attacker needs to find a collision with the first half of the digest. attacker needs to find a collision with the first half of the digest.
Similar attacks can be mounted against parameterized algorithm Similar attacks can be mounted against parameterized algorithm
identifiers. When looking at randomized hash functions, such as the identifiers. When looking at randomized hash functions, such as the
example in [RFC6210], the algorithm identifier parameter includes a example in [RFC6210], the algorithm identifier parameter includes a
random value that can be manipulated by an attacker looking for random value that can be manipulated by an attacker looking for
collisions. Some other algorithm identifiers include complex collisions. Some other algorithm identifiers include complex
parameter structures, and each value provides another opportunity for parameter structures, and each value provides another opportunity for
manipulation by an attacker. manipulation by an attacker.
This document makes two updates to CMS to provide similar protection This document makes two updates to CMS to provide protection for the
for the algorithm identifier. First, it mandates a convention algorithm identifier. First, it mandates a convention followed by
followed by many implementations by requiring the originator to use many implementations by requiring the originator to use the same hash
the same hash algorithm to compute the digest of the message content algorithm to compute the digest of the message content and the digest
and the digest of signed attributes. Second, it recommends that the of signed attributes. Second, it recommends that the originator
originator include the CMSAlgorithmProtection attribute [RFC6211]. include the CMSAlgorithmProtection attribute [RFC6211].
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Required use the same hash algorithm 3. Required use the same hash algorithm
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set. set.
NEW: NEW:
digestAlgorithm identifies the message digest algorithm, and any digestAlgorithm identifies the message digest algorithm, and any
associated parameters, used by the signer. The message digest is associated parameters, used by the signer. The message digest is
computed on either the content being signed or the content computed on either the content being signed or the content
together with the signedAttrs using the process described in together with the signedAttrs using the process described in
Section 5.4. The message digest algorithm SHOULD be among those Section 5.4. The message digest algorithm SHOULD be among those
listed in the digestAlgorithms field of the associated SignerData. listed in the digestAlgorithms field of the associated SignerData.
If signedAttrs field is present in the SignerInfo, then the same If the signedAttrs field is present in the SignerInfo, then the
digest algorithm MUST be used to compute both the digest of the same digest algorithm MUST be used to compute both the digest of
SignedData encapContentInfo eContent, which is carried in the the SignedData encapContentInfo eContent, which is carried in the
message-digest attribute, and the digest of the DER-encoded message-digest attribute, and the digest of the DER-encoded
signedAttrs, which is passed to the signature algorithm. signedAttrs, which is passed to the signature algorithm.
Implementations MAY fail to validate signatures that use a digest Implementations MAY fail to validate signatures that use a digest
algorithm that is not included in the SignedData digestAlgorithms algorithm that is not included in the SignedData digestAlgorithms
set. set.
3.2. RFC 5652, Section 5.4 3.2. RFC 5652, Section 5.4
Add the following paragraph as the second paragraph in Section 5.4: Add the following paragraph as the second paragraph in Section 5.4:
ADD: ADD:
When the signedAttrs field is present, the same digest algorithm When the signedAttrs field is present, the same digest algorithm
MUST be used to compute the digest of the encapContentInfo MUST be used to compute the digest of the encapContentInfo
eContent OCTET STRING, which is carried in the message-digest eContent OCTET STRING, which is carried in the message-digest
attribute, and the collection of attributes that are signed. attribute, and the digest of the collection of attributes that are
signed.
nit: there may be a grammar nit here, relating to the parallelism of
"compute the digest of" - I think "the collection of attributes that
are signed" should also have an "of" or "digest of" prefix.
3.3. RFC 5652, Section 5.6 3.3. RFC 5652, Section 5.6
Change the paragraph discussing the signed attributes as follows: Change the paragraph discussing the signed attributes as follows:
OLD: OLD:
The recipient MUST NOT rely on any message digest values computed The recipient MUST NOT rely on any message digest values computed
by the originator. If the SignedData signerInfo includes by the originator. If the SignedData signerInfo includes
signedAttributes, then the content message digest MUST be signedAttributes, then the content message digest MUST be
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3.5. Timestamp Compatibility Considerations 3.5. Timestamp Compatibility Considerations
The new requirement introduced above might lead to compatibility The new requirement introduced above might lead to compatibility
issues for timestamping systems when the originator does not wish to issues for timestamping systems when the originator does not wish to
share the message content with the Time Stamp Authority (TSA) share the message content with the Time Stamp Authority (TSA)
[RFC3161]. In this situation, the originator sends a TimeStampReq to [RFC3161]. In this situation, the originator sends a TimeStampReq to
the TSA that includes a MessageImprint, which consists of a digest the TSA that includes a MessageImprint, which consists of a digest
algorithm identifier and a digest value, then the TSA uses the algorithm identifier and a digest value, then the TSA uses the
originator-provided digest in the MessageImprint. originator-provided digest in the MessageImprint.
When producing the TimeStampToken, the TSA MUST use same digest When producing the TimeStampToken, the TSA MUST use the same digest
algorithm to compute the digest of the encapContentInfo eContent, algorithm to compute the digest of the encapContentInfo eContent,
which is an OCTET STRING that contains the TSTInfo, and the message- which is an OCTET STRING that contains the TSTInfo, and the message-
digest attribute within the SignerInfo. digest attribute within the SignerInfo.
To ensure that TimeStampToken values that were generated before this To ensure that TimeStampToken values that were generated before this
update remain valid, no requirement is placed on a TSA to ensure that update remain valid, no requirement is placed on a TSA to ensure that
the digest algorithm for the TimeStampToken matches the digest the digest algorithm for the TimeStampToken matches the digest
algorithm for the MessageImprint embedded within the TSTTokenInfo. algorithm for the MessageImprint embedded within the TSTInfo.
4. Recommend inclusion of the CMSAlgorithmProtection attribute 4. Recommended inclusion of the CMSAlgorithmProtection attribute
This section updates [RFC5652] to recommend that the originator This section updates [RFC5652] to recommend that the originator
include the CMSAlgorithmProtection attribute [RFC6211] whenever include the CMSAlgorithmProtection attribute [RFC6211] whenever
signed attributes or authenticated attributes are present. signed attributes or authenticated attributes are present.
4.1. RFC 5652, Section 14 4.1. RFC 5652, Section 14
Add the following paragraph as the eighth paragraph in Section 14: Add the following paragraph as the eighth paragraph in Section 14:
ADD: ADD:
While no known algorithm substitution attacks are known at this While there are no known algorithm substitution attacks today, the
time, the inclusion of the algorithm identifiers used by the inclusion of the algorithm identifiers used by the originator as a
originator as a signed attribute or an authenticated attribute signed attribute or an authenticated attribute makes such an
makes such an attack significantly more difficult. Therefore, the attack significantly more difficult. Therefore, the originator of
originator of a signed-data content type that includes signed a signed-data content type that includes signed attributes SHOULD
include the CMSAlgorithmProtection attribute [RFC6211] as one of
the signed attributes. Likewise, the originator of an
authenticated-data content type that includes authenticated
attributes SHOULD include the CMSAlgorithmProtection attribute attributes SHOULD include the CMSAlgorithmProtection attribute
[RFC6211] as one of the signed attributes. Likewise, the [RFC6211] as one of the authenticated attributes.
originator of an authenticated-data content type that includes
authenticated attributes SHOULD include the CMSAlgorithmProtection
attribute [RFC6211] as one of the authenticated attributes.
5. IANA Considerations 5. IANA Considerations
This document makes no requests of the IANA. This document makes no requests of the IANA.
6. Security Considerations 6. Security Considerations
The security properties of the CMS [RFC5652] signed-data and The security properties of the CMS [RFC5652] signed-data and
authenticated-data content types are updated to ensure that algorithm authenticated-data content types are updated to offer protection for
identifiers are adequately protected, which makes algorithm algorithm identifiers, which makes algorithm substitution attacks
substitution attacks significantly more difficult. significantly more difficult.
For the signed-data content type, the improvements specified in this For the signed-data content type, the improvements specified in this
document force an attacker to mount a hash algorithm substitution document force an attacker to mount a hash algorithm substitution
attack on the overall signature, not just on the message digest of attack on the overall signature, not just on the message digest of
the encapContentInfo eContent. the encapContentInfo eContent.
Some digital signature algorithms have prevented hash function Some digital signature algorithms have prevented hash function
substitutions by including a digest algorithm identifier as an input substitutions by including a digest algorithm identifier as an input
to the signature algorithm. As discussed in [HASHID], such a to the signature algorithm. As discussed in [HASHID], such a
"firewall" may not be effective or even possible with newer signature "firewall" may not be effective or even possible with newer signature
algorithms. For example, RSASSA-PKCS1-v1_5 [RFC8017] protects the algorithms. For example, RSASSA-PKCS1-v1_5 [RFC8017] protects the
digest algorithm identifier, but RSASSA-PSS [RFC8017] does not. digest algorithm identifier, but RSASSA-PSS [RFC8017] does not.
Therefore, it remains important that a signer have a way to signal to Therefore, it remains important that a signer have a way to signal to
a recipient which digest algorithms are allowed to be used in a recipient which digest algorithms are allowed to be used in
conjunction with the verification of an overall signature. This conjunction with the verification of an overall signature. This
signalling can be done as part of the specification of the signature signaling can be done as part of the specification of the signature
algorithm in an X.509v3 certificate extension [RFC5280], or some algorithm, in an X.509v3 certificate extension [RFC5280], or some
other means. The Digital Signature Standard (DSS) [DSS] takes the other means. The Digital Signature Standard (DSS) [DSS] takes the
first approach by requiring the use of an "approved" one-way hash first approach by requiring the use of an "approved" one-way hash
algorithm. algorithm.
For the authenticated-data content type, the improvements specified For the authenticated-data content type, the improvements specified
in this document force an attacker to mount a MAC algorithm in this document force an attacker to mount a MAC algorithm
substitution attack, which is difficult because the attacker does not substitution attack, which is difficult because the attacker does not
know the authentication key. know the authentication key.
The CMSAlgorithmProtection attribute [RFC6211] offers protection for The CMSAlgorithmProtection attribute [RFC6211] offers protection for
the algorithm identifiers used in the signed-data and authenticated- the algorithm identifiers used in the signed-data and authenticated-
data content types. However, no protection is provided for the data content types. However, no protection is provided for the
algorithm identifiers in the enveloped-data, digested-data, or algorithm identifiers in the enveloped-data, digested-data, or
encrypted-data content types. Likewise, The CMSAlgorithmProtection encrypted-data content types. Likewise, The CMSAlgorithmProtection
attribute provides no protection for the algorithm identifiers used attribute provides no protection for the algorithm identifiers used
in the authenticated-enveloped-data content type defined in in the authenticated-enveloped-data content type defined in
[RFC5083]. [RFC5083]. A mechanism for algorithm identifier protection for these
content types is work for the future.
7. Acknowledgements 7. Acknowledgements
Many thanks to Jim Schaad and Peter Gutmann; without knowing it, they Many thanks to Jim Schaad and Peter Gutmann; without knowing it, they
motivated me to write this document. Thanks to Roman Danyliw for motivated me to write this document. Thanks to Roman Danyliw, Ben
careful review and editorial suggestions. Kaduk, and Peter Yee for their careful review and editorial
suggestions.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3161] Adams, C., Cain, P., Pinkas, D., and R. Zuccherato,
"Internet X.509 Public Key Infrastructure Time-Stamp
Protocol (TSP)", RFC 3161, DOI 10.17487/RFC3161, August
2001, <https://www.rfc-editor.org/info/rfc3161>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009, RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>. <https://www.rfc-editor.org/info/rfc5652>.
[RFC6211] Schaad, J., "Cryptographic Message Syntax (CMS) Algorithm [RFC6211] Schaad, J., "Cryptographic Message Syntax (CMS) Algorithm
Identifier Protection Attribute", RFC 6211, Identifier Protection Attribute", RFC 6211,
DOI 10.17487/RFC6211, April 2011, DOI 10.17487/RFC6211, April 2011,
<https://www.rfc-editor.org/info/rfc6211>. <https://www.rfc-editor.org/info/rfc6211>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
skipping to change at page 8, line 9 skipping to change at page 8, line 24
8.2. Informative References 8.2. Informative References
[DSS] National Institute of Standards and Technology (NIST), [DSS] National Institute of Standards and Technology (NIST),
"Digital Signature Standard (DSS)", FIPS "Digital Signature Standard (DSS)", FIPS
Publication 186-4, July 2013. Publication 186-4, July 2013.
[HASHID] Kaliski, B., "On Hash Function Firewalls in Signature [HASHID] Kaliski, B., "On Hash Function Firewalls in Signature
Schemes", Lecture Notes in Computer Science, Volume 2271, Schemes", Lecture Notes in Computer Science, Volume 2271,
DOI 10.1007/3-540-45760-7_1, February 2002. DOI 10.1007/3-540-45760-7_1, February 2002.
[RFC3161] Adams, C., Cain, P., Pinkas, D., and R. Zuccherato,
"Internet X.509 Public Key Infrastructure Time-Stamp
Protocol (TSP)", RFC 3161, DOI 10.17487/RFC3161, August
2001, <https://www.rfc-editor.org/info/rfc3161>.
[RFC5083] Housley, R., "Cryptographic Message Syntax (CMS) [RFC5083] Housley, R., "Cryptographic Message Syntax (CMS)
Authenticated-Enveloped-Data Content Type", RFC 5083, Authenticated-Enveloped-Data Content Type", RFC 5083,
DOI 10.17487/RFC5083, November 2007, DOI 10.17487/RFC5083, November 2007,
<https://www.rfc-editor.org/info/rfc5083>. <https://www.rfc-editor.org/info/rfc5083>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>. <https://www.rfc-editor.org/info/rfc5280>.
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