Updates for RSAES-OAEP and RSASSA-PSS Algorithm Parameters

Abstract

This document updates RFC 4055. It updates the conventions for using the RSA Encryption Scheme - Optimal Asymmetric Encryption Padding (RSAES-OAEP) key transport algorithm in the Internet X.509 Public Key Infrastructure (PKI). Specifically, it updates the conventions for algorithm parameters in an X.509 certificate's subjectPublicKeyInfo field.

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/rfc5756.

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1. Introduction

RFC 4055 specifies conventions for using the RSA Encryption Scheme - Optimal Asymmetric Encryption Padding (RSAES-OAEP) key transport algorithm in the Internet X.509 Public Key Infrastructure (PKI). It provides algorithm identifiers and parameters for RSAES-OAEP.

This document updates the conventions for RSAES-OAEP parameters in the subjectPublicKeyInfo field of an X.509 certificate. The PKIX WG Elliptic Curve Cryptography (ECC) design team recommended that Key Derivation Functions (KDFs) should not be constrained within a certificate; rather, KDF constraints should be negotiated in protocols that need to employ certificates.

Only two paragraphs in [RFC4055] discuss RSAES-OAEP parameters in X.509 certificates: the second paragraph of Section 4 and the first paragraph of Section 4.1. This document only updates these two paragraphs. Section 3 updates the second paragraph in Section 4 of [RFC4055], while Section 4 updates the second paragraph in Section 4.1 of [RFC4055]. "Old:" prefaces the text to be replaced and "New:" prefaces the replacement text.

This document also replaces incorrect references to the publicKeyAlgorithms field in Section 3 with references to the parameters field in the subjectPublicKeyInfo algorithm field. Section 3 also rewords the second and third paragraphs for clarity.

1.1. Conventions Used in This Document

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 [RFC2119].

2. Changes to Section 3 (Second and Third Paragraphs)

This change clarifies the placement of RSASSA-PSS-params in the signature, signatureAlgorithm, and subjectPublicKeyInfo fields for certification authority (CA) and end-entity (EE) certificates. It also clarifies the placement of RSASSA-PSS-params in the signatureAlgorithm field in certificate revocation lists (CRLs).

Old:

CAs that issue certificates with the id-RSASSA-PSS algorithm identifier SHOULD require the presence of parameters in the publicKeyAlgorithms field if the cA boolean flag is set in the basic constraints certificate extension. CAs MAY require that the parameters be present in the publicKeyAlgorithms field for end-entity certificates.

CAs that use the RSASSA-PSS algorithm for signing certificates SHOULD include RSASSA-PSS-params in the subjectPublicKeyInfo algorithm parameters in their own certificates. CAs that use the RSASSA-PSS algorithm for signing certificates or CRLs MUST include RSASSA-PSS- params in the signatureAlgorithm parameters in the TBSCertificate or TBSCertList structures.

New:

When the id-RSASSA-PSS object identifier appears in the TBSCertificate or TBSCertList signature algorithm field, then the RSASSA-PSS-params structure MUST be included in the TBSCertificate or TBSCertList signature parameters field.

When the id-RSASSA-PSS object identifier appears in the TBSCertificate subjectPublicKeyInfo algorithm field of CA certificates, then the parameters field SHOULD include the RSASSA- PSS-params structure. When the id-RSASSA-PSS object identifier appears in the TBSCertificate subjectPublicKeyInfo algorithm field of EE certificates, then the parameters field MAY include the RSASSA- PSS-params structure.

All certificates and CRLs signed by a CA that supports the id-RSASSA- PSS algorithm MUST include the RSASSA-PSS-params in the signatureAlgorithm parameters in Certificate and CertList structures, respectively.

3. Changes to Section 4 (Second Paragraph)

This change prohibits the inclusion of RSAES-OAEP-params in the subjectPublicKeyInfo field. This was done because a) it does not affect interoperability and b) it aligns with PKIX practice to not include limitations on how the public key can be used in subjectPublicKeyInfo. A poll of implementers was taken and there were no objections to this change as it did not affect current implementations.

Old:

CAs that issue certificates with the id-RSAES-OAEP algorithm identifier SHOULD require the presence of parameters in the publicKeyAlgorithms field for all certificates. Entities that use a certificate with a publicKeyAlgorithm value of id-RSA-OAEP where the parameters are absent SHOULD use the default set of parameters for RSAES-OAEP-params. Entities that use a certificate with a publicKeyAlgorithm value of rsaEncryption SHOULD use the default set of parameters for RSAES-OAEP-params.

New:

CAs that issue certificates with the id-RSAES-OAEP algorithm identifier MUST NOT include parameters in the subjectPublicKeyInfo algorithm field.

4. Changes to Section 4.1 (First Paragraph)

This change prohibits the inclusion of parameters in the subjectPublicKeyInfo field. This was done because a) it does not affect interoperability and b) it aligns with PKIX practice to not include limitations on how the public key can be used in subjectPublicKeyInfo. A poll of implementers was taken and there were no objections to this change as it did not affect current implementations.

Old:

When id-RSAES-OAEP is used in an AlgorithmIdentifier, the parameters MUST employ the RSAES-OAEP-params syntax. The parameters may be either absent or present when used as subject public key information.

The parameters MUST be present when used in the algorithm identifier associated with an encrypted value.

New:

When id-RSAES-OAEP is used in an AlgorithmIdentifier, the parameters MUST employ the RSAES-OAEP-params syntax. The parameters MUST be absent when used in the subjectPublicKeyInfo field. The parameters MUST be present when used in the algorithm identifier associated with an encrypted value.

5. Security Considerations

The security considerations from [RFC4055] apply.

If the RSAES-OAEP-params are negotiated, then the negotiation mechanism needs to provide integrity for these parameters. For example, an S/MIME Agent can advertise their capabilities in the SMIMECapabilities attribute, which is either a signed attribute [RFC5751] or a certificate extension [RFC4262].

6. References

6.1. Normative References

   [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
   
                 Requirement Levels", BCP 14, RFC 2119, March 1997.
   
   [RFC4055]     Schaad, J., Kaliski, B., and R. Housley, "Additional
                 Algorithms and Identifiers for RSA Cryptography for use
                 in the Internet X.509 Public Key Infrastructure
                 Certificate and Certificate Revocation List (CRL)
                 Profile", RFC 4055, June 2005.

6.2. Informative References

   [RFC4262]     Santesson, S., "X.509 Certificate Extension for
                 Secure/Multipurpose Internet Mail Extensions (S/MIME)
                 Capabilities", RFC 4262, December 2005.
   
   [RFC5751]     Ramsdell, B. and S. Turner, "Secure/Multipurpose
                 Internet Mail Extensions (S/MIME) Version 3.2 Message
                 Specification", RFC 5751, January 2010.

Authors' Addresses

Sean Turner
IECA, Inc.
3057 Nutley Street, Suite 106
Fairfax, VA 22031
USA

EMail:

          turners@ieca.com

Kelvin Yiu
Microsoft
One Microsoft Way
Redmond, WA 98052-6399
USA

EMail:

          kelviny@microsoft.com

Daniel R. L. Brown
Certicom Corp
5520 Explorer Drive #400
Mississauga, ON L4W 5L1
CANADA

EMail:

          dbrown@certicom.com

Russ Housley
Vigil Security, LLC
918 Spring Knoll Drive
Herndon, VA 20170
USA

EMail:

          housley@vigilsec.com

Tim Polk
NIST
Building 820, Room 426
Gaithersburg, MD 20899
USA

EMail:

          wpolk@nist.gov