Additional Cryptographic Message Syntax (CMS) Revocation Information Choices
Lets a CMS message carry OCSP and SCVP answers about revoked certificates, not just CRLs.
Turner, S. and R. Housley, "Additional Cryptographic Message Syntax (CMS) Revocation Information Choices", RFC 5940, DOI 10.17487/RFC5940, August 2010, <https://www.rfc-editor.org/info/rfc5940>.
@misc{rfc5940,
series = {Request for Comments},
number = 5940,
howpublished = {RFC 5940},
publisher = {RFC Editor},
doi = {10.17487/RFC5940},
url = {https://www.rfc-editor.org/info/rfc5940},
author = {S. Turner and R. Housley},
title = {{Additional Cryptographic Message Syntax (CMS) Revocation Information Choices}},
pagetotal = 9,
year = 2010,
month = aug,
} RFC text
Contents
Internet Engineering Task Force (IETF) S. Turner
Request for Comments: 5940 IECA
Category: Standards Track R. Housley
ISSN: 2070-1721 Vigil Security
August 2010
Additional Cryptographic Message Syntax (CMS)
Revocation Information Choices
Abstract
The Cryptographic Message Syntax (CMS) allows revocation information
to be conveyed as part of the SignedData, EnvelopedData,
AuthenticatedData, and AuthEnvelopedData content types. The
preferred format for revocation information is the Certificate
Revocation List (CRL), but an extension mechanism supports other
revocation information formats. This document defines two additional
revocation information formats for Online Certificate Status Protocol
(OCSP) responses and Server-Based Certificate Validation Protocol
(SCVP) requests and responses.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5940.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
1. Introduction
The RevocationInfoChoices type defined in [CMS] provides a set of
revocation status information alternatives, which allows revocation
information to be conveyed as part of the SignedData, EnvelopedData,
AuthenticatedData, and AuthEnvelopedData content types. The intent
is to provide information sufficient to determine whether the
certificates and attribute certificates carried elsewhere in the CMS-
protected content have been revoked. There may be more revocation
status information than necessary or there may be less revocation
status information than necessary.
X.509 Certificate Revocation Lists (CRLs) [PROFILE] are the primary
source of revocation status information, but any other revocation
information format can be supported. This document specifies two
other formats: Online Certificate Status Protocol (OCSP) responses
[OCSP] and Server-Based Certificate Validation Protocol (SCVP)
requests and responses [SCVP].
Section 2 discusses the RevocationInformation structure. Section 3
defines a mechanism to carry OCSP responses. Section 4 defines a
mechanism to carry SCVP requests and responses. Appendix A provides
the normative ASN.1 syntax for the two mechanisms.
1.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [WORDS].
2. Revocation Information
For convenience, the ASN.1 definition of the RevocationInfoChoices
type from [CMS] is repeated here:
RevocationInfoChoices ::= SET OF RevocationInfoChoice
RevocationInfoChoice ::= CHOICE {
crl CertificateList,
other [1] IMPLICIT OtherRevocationInfoFormat }
OtherRevocationInfoFormat ::= SEQUENCE {
otherRevInfoFormat OBJECT IDENTIFIER,
otherRevInfo ANY DEFINED BY otherRevInfoFormat }
The other CHOICE MUST be used to convey OCSP responses, SCVP
requests, and SCVP responses.
This document defines the id-ri arc under which the revocation
information formats are defined. The id-ri object identifier is:
id-ri OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) ri(16) }
NOTE: Numbers 1 and 3 were assigned to CRL and Delta CRL. These two
numbers are not used because these formats use the
RevocationInfoChoice crl CHOICE when included in CMS [CMS].
3. OCSP Response
To carry an OCSP response, the otherRevInfoFormat is set to
id-ri-ocsp-response, which has the following ASN.1 definition:
id-ri-ocsp-response OBJECT IDENTIFIER ::= { id-ri 2 }
In this case, otherRevInfo MUST carry the OCSP response using the
OCSPResponse type defined in [OCSP]. The responseStatus field MUST
be successful and the responseBytes field MUST be present.
4. SCVP Request and Response
Unlike OSCP, SCVP permits unprotected and protected responses, where
protected responses can be digitally signed or include message
authentication codes. While this provides more flexibility, it
complicates implementations when an SCVP response can be validated by
entities other than the entity that generated the SCVP request. If a
lower layer provides authentication and integrity for the client-
server interaction and the response is not protected, then a third
party cannot validate the response because there is no way to know
that the response was returned over a protected connection. If a
message authentication code is used, then the third party will be
unable to validate the message authentication code because it does
not possess the necessary private key. For these reasons, SCVP
responses sent to a third party MUST be signed by the SCVP server so
that the third party can validate them.
SCVP response validation requires matching it to the SCVP request.
This means that the SCVP request MUST always be included with the
response. SCVP permits the client to retain the response, and SCVP
permits the request to be returned in the response (in the requestReq
field). The request need not be protected for matching to be
performed; nonces and certIds can be checked.
To carry the SCVP request and response, the otherRevInfoFormat is set
to id-ri-scvp, which has the following ASN.1 definition:
id-ri-scvp OBJECT IDENTIFIER ::= { id-ri 4 }
In this case, the otherRevInfo MUST carry both the SCVP request and
response with the following structure:
SCVPReqRes ::= SEQUENCE {
request [0] EXPLICIT ContentInfo OPTIONAL,
response ContentInfo }
The SCVPReqRes has the following fields:
o request contains the SCVP request. It contains the unprotected
request, authenticated request, or the signed request. The request
MUST be present if the response does not include the requestRef
fullRequest field.
o response contains the SCVP response. It MUST contain the signed
response. Additionally, the responseStatus MUST be okay.
Unprotected and authenticated responses MUST NOT be included.
5. Security Considerations
The security considerations of [CMS], [CMS-ASN], [OCSP], [SCVP], and
[PROFILE-ASN] apply.
To locally store unprotected or authenticated SCVP responses, a
client can encapsulate the unprotected or authenticated SCVP response
in a SignedData. It is a matter of local policy whether these SCVP
responses that are encapsulated and signed by the client are
considered valid by another entity.
6. IANA Considerations
This document makes use of object identifiers. These object
identifiers are defined in an arc delegated by IANA to the PKIX
Working Group. When the PKIX Working Group closes, this arc and its
registration procedures will be transferred to IANA. No further
action by IANA is necessary for this document or any anticipated
updates.
7. References
7.1. Normative References
[CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
5652, September 2009.
[CMS-ASN] Hoffman, P. and J. Schaad, "New ASN.1 Modules for
Cryptographic Message Syntax (CMS) and S/MIME", RFC 5911,
June 2010.
[OCSP] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C.
Adams, "X.509 Internet Public Key Infrastructure Online
Certificate Status Protocol - OCSP", RFC 2560, June 1999.
[PROFILE-ASN]
Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
June 2010.
[SCVP] Freeman, T., Housley, R., Malpani, A., Cooper, D., and W.
Polk, "Server-Based Certificate Validation Protocol
(SCVP)", RFC 5055, December 2007.
[WORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[X.680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824- 1:2002.
Information Technology - Abstract Syntax Notation One.
[X.681] ITU-T Recommendation X.681 (2002) | ISO/IEC 8824- 2:2002.
Information Technology - Abstract Syntax Notation One:
Information Object Specification.
[X.682] ITU-T Recommendation X.682 (2002) | ISO/IEC 8824- 3:2002.
Information Technology - Abstract Syntax Notation One:
Constraint Specification.
[X.683] ITU-T Recommendation X.683 (2002) | ISO/IEC 8824- 4:2002.
Information Technology - Abstract Syntax Notation One:
Parameterization of ASN.1 Specifications, 2002.
7.2. Informative References
[PROFILE] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
Appendix A. ASN.1 Modules
Appendix A.1 provides the normative ASN.1 definitions for the
structures described in this specification using ASN.1 as defined in
[X.680] for compilers that support the 1988 ASN.1.
Appendix A.2 provides informative ASN.1 definitions for the
structures described in this specification using ASN.1 as defined in
[X.680], [X.681], [X.682], and [X.683] for compilers that support the
2002 ASN.1. This appendix contains the same information as Appendix
A.1 in a more recent (and precise) ASN.1 notation, however Appendix
A.1 takes precedence in case of conflict.
A.1. 1988 ASN.1 Module
CMS-Other-RIs-2009-88
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-cms-otherRIs-2009-88(63)
}
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL
IMPORTS
-- FROM CMS [CMS]
ContentInfo
FROM CryptographicMessageSyntax2004
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) cms-2004(24) }
;
id-ri OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) ri(16) }
-- RevocationInfoChoice for OCSP response
-- OID included in otherRevInfoFormat
-- signed OCSP response included in otherRevInfo
id-ri-ocsp-response OBJECT IDENTIFIER ::= { id-ri 2 }
-- RevocationInfoChoice for SCVP response
-- OID included in otherRevInfoFormat
-- SCVPReqRes included in otherRevInfo
id-ri-scvp OBJECT IDENTIFIER ::= { id-ri 4 }
SCVPReqRes ::= SEQUENCE {
request [0] EXPLICIT ContentInfo OPTIONAL,
response ContentInfo }
END
A.2. 2002 ASN.1 Module
CMS-Other-RIs-2009-02
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-cms-otherRIs-2009-93(64)
}
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORT ALL
IMPORTS
-- FROM [PROFILE-ASN]
OCSPResponse
FROM OCSP-2009
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-ocsp-02(48) }
-- FROM [CMS-ASN]
ContentInfo, OTHER-REVOK-INFO
FROM CryptographicMessageSyntax-2009
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) id-mod-cms-2004-02(41) }
;
-- Defines OCSP and SCVP formats for RevocationInfoChoice
SupportedOtherRevokInfo OTHER-REVOK-INFO ::= {
ri-ocsp-response |
ri-scvp,
... }
ri-ocsp-response OTHER-REVOK-INFO ::= {
OCSPResponse IDENTIFIED BY id-ri-ocsp-response }
id-ri OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) ri(16) }
id-ri-ocsp-response OBJECT IDENTIFIER ::= { id-ri 2 }
ri-scvp OTHER-REVOK-INFO ::= {
SCVPReqRes IDENTIFIED BY id-ri-scvp }
id-ri-scvp OBJECT IDENTIFIER ::= { id-ri 4 }
SCVPReqRes ::= SEQUENCE {
request [0] EXPLICIT ContentInfo OPTIONAL,
response ContentInfo }
END
Authors' Addresses
Sean Turner
IECA, Inc.
3057 Nutley Street, Suite 106
Fairfax, VA 22031
USA
EMail: turners@ieca.com
Russ Housley
Vigil Security, LLC
918 Spring Knoll Drive
Herndon, VA 20170
USA
EMail: housley@vigilsec.com
AI ELI5
On this page
§1Why CMS Needs More Revocation Formats
The RevocationInfoChoices type defined in RFC 5652 lets revocation information travel inside the SignedData, EnvelopedData, AuthenticatedData and AuthEnvelopedData content types. The goal is to give a receiver enough information to decide whether the certificates and attribute certificates in the protected content have been revoked.
X.509 CRLs are the primary source of revocation status information, but the CMS design lets any other format be supported. This RFC specifies two: Online Certificate Status Protocol (OCSP) responses and Server-Based Certificate Validation Protocol (SCVP) requests and responses. It also notes that there may be more revocation status information than necessary, or less.
When you send a signed message, you can staple proof that the sender's ID is still good. This RFC adds two new kinds of proof you can staple.
§2The RevocationInfoChoices Structure
A RevocationInfoChoices is a set of RevocationInfoChoice values. Each is either a crl (a CertificateList) or an other value of type OtherRevocationInfoFormat. That type pairs an object identifier, otherRevInfoFormat, with data, otherRevInfo, whose type depends on the identifier.
The RFC says the other choice MUST be used to carry OCSP responses, SCVP requests and SCVP responses.
The RFC defines the id-ri arc, under the PKIX arc, for these formats. Numbers 1 and 3 were assigned to CRL and Delta CRL. They are not used because those formats already travel in the crl choice.
The message has a slot for the standard form and a 'something else' slot. Each item in the 'something else' slot carries a label that says what kind of thing it is.
- RevocationInfoChoices SET OF RevocationInfoChoice
- crl CertificateList (CRLs and Delta CRLs)
- other OtherRevocationInfoFormat
- id-ri-ocsp-response { id-ri 2 } OCSPResponse
- id-ri-scvp { id-ri 4 } SCVPReqRes
§3Carrying an OCSP Response
To carry an OCSP response, otherRevInfoFormat is set to id-ri-ocsp-response, which is { id-ri 2 }. The otherRevInfo field MUST then hold the response as the OCSPResponse type defined in RFC 2560.
Two constraints apply. The responseStatus field MUST be successful, and the responseBytes field MUST be present. In other words, an error response has no place in the message.
If you attach an OCSP answer, it has to be a real answer that says 'here is the result', not a note that says 'something went wrong'.
§4Carrying SCVP Requests and Responses
SCVP is defined in RFC 5055. Unlike OCSP, SCVP permits unprotected and protected responses, and protected ones can be digitally signed or carry message authentication codes. That flexibility complicates things when someone other than the original requester validates the response. An unprotected response leaves a third party unable to know it came over a protected connection. A message authentication code cannot be checked by a third party who lacks the necessary key. So SCVP responses sent to a third party MUST be signed by the SCVP server.
Validating an SCVP response means matching it to its request, so the request MUST always be included with the response. The request need not be protected for this, since nonces and certIds can be checked.
The format is identified by id-ri-scvp, which is { id-ri 4 }, and the data is an SCVPReqRes sequence. The request field holds the unprotected, authenticated or signed request, and MUST be present if the response does not include the requestRef fullRequest field. The response field MUST hold the signed response with responseStatus of okay. Unprotected and authenticated responses MUST NOT be included.
If you show someone else an answer from a helper, the answer has to carry the helper's signature and the original question, so they can trust it and see what it was answering.
§5Security Considerations
The security considerations of the CMS, OCSP and SCVP specifications, and of the ASN.1 module documents RFC 5911 and RFC 5912, apply.
The RFC adds one point. To store an unprotected or authenticated SCVP response locally, a client can wrap it in a SignedData. Whether another entity treats such a client-signed response as valid is a matter of local policy.
If you keep a copy of a note and sign it yourself, whether other people believe it is up to them.
§6IANA and ASN.1 Modules
The object identifiers come from an arc delegated by IANA to the PKIX Working Group. When that group closes, the arc and its registration procedures will be transferred to IANA. No further action by IANA is necessary for this document.
Appendix A gives the ASN.1. Appendix A.1 is a normative module for compilers that support the 1988 ASN.1. Appendix A.2 is an informative module in the 2002 ASN.1 notation. It carries the same information, and A.1 takes precedence if they conflict.
The special label numbers are handed out from a list the standards group keeps, and nothing new needs to be registered.