Internet Engineering Task Force (IETF)                         G. Huston
Request for Comments: 7935                            G. Michaelson, Ed.
Obsoletes: 6485                                                    APNIC
Category: Standards Track                                    August 2016
ISSN: 2070-1721


                The Profile for Algorithms and Key Sizes
           for Use in the Resource Public Key Infrastructure

Abstract

   This document specifies the algorithms, algorithms' parameters,
   asymmetric key formats, asymmetric key size, and signature format for
   the Resource Public Key Infrastructure (RPKI) subscribers that
   generate digital signatures on certificates, Certificate Revocation
   Lists (CRLs), Cryptographic Message Syntax (CMS) signed objects and
   certification requests as well as for the relying parties (RPs) that
   verify these digital signatures.

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 7841.

   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/rfc7935.

Copyright Notice

   Copyright (c) 2016 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
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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Algorithms  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Asymmetric Key Pair Formats . . . . . . . . . . . . . . . . .   4
     3.1.  Public Key Format . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Private Key Format  . . . . . . . . . . . . . . . . . . .   5
   4.  Signature Format  . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Additional Requirements . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Changes Applied to RFC 6485 . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   This document specifies:

      *  the digital signature algorithm and parameters;

      *  the hash algorithm and parameters;

      *  the public and private key formats; and,

      *  the signature format

   used by Resource Public Key Infrastructure (RPKI) [RFC6480]
   subscribers when they apply digital signatures to certificates and
   Certificate Revocation Lists (CRLs) [RFC5280], Cryptographic Message
   Syntax (CMS) signed objects [RFC5652] (e.g., Route Origin
   Authorizations (ROAs) [RFC6482] and manifests [RFC6486]), and
   certification requests [RFC2986] [RFC4211].  Relying parties (RPs)
   also use the algorithms defined in this document to verify RPKI
   subscribers' digital signatures [RFC6480].

   The RPKI profiles and specification documents that reference RFC 6485
   now refer to this document; these documents include the RPKI
   Certificate Policy (CP) [RFC6484], the RPKI Certificate Profile
   [RFC6487], the RPKI Architecture [RFC6480], and the Signed Object
   Template for the RPKI [RFC6488].  Familiarity with these documents is
   assumed.

1.1.  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 [RFC2119].

2.  Algorithms

   Two cryptographic algorithms are used in the RPKI:

      *  The signature algorithm used in certificates, CRLs, CMS signed
         objects, and certification requests is RSA Public-Key
         Cryptography Standards (PKCS) #1 Version 1.5 (sometimes
         referred to as "RSASSA-PKCS1-v1_5") from Section 8.2 of
         [RFC3447].

      *  The hashing algorithm used in certificates, CRLs, CMS signed
         objects and certification requests is SHA-256 [SHS] (see note
         below).

         NOTE: The exception is the use of SHA-1 [SHS] when CAs generate
         authority and subject key identifiers [RFC6487].

   In certificates, CRLs, and certification requests the hashing and
   digital signature algorithms are identified together, i.e., "RSA
   PKCS #1 v1.5 with SHA-256" or more simply "RSA with SHA-256".  The
   Object Identifier (OID) sha256WithRSAEncryption from [RFC4055] MUST
   be used in these products.

   The OID is in the following locations:

      In the certificate, the OID appears in the signature and
      signatureAlgorithm fields [RFC4055].

      In the CRL, the OID appears in the signatureAlgorithm field
      [RFC4055].

      In a certification request, the OID appears in the PKCS #10
      signatureAlgorithm field [RFC2986], or in the Certificate Request
      Message Format (CRMF) POPOSigningKey algorithmIdentifier field
      [RFC4211].

   In CMS SignedData, the hashing (message digest) and digital signature
   algorithms are identified separately.  The object identifier and
   parameters for SHA-256 (as defined in [RFC5754]) MUST be used for the
   SignedData digestAlgorithms field and the SignerInfo digestAlgorithm
   field.  The object identifier and parameters for rsaEncryption
   [RFC3370] MUST be used for the SignerInfo signatureAlgorithm field
   when generating CMS SignedData objects.  RPKI implementations MUST
   accept either rsaEncryption or sha256WithRSAEncryption for the
   SignerInfo signatureAlgorithm field when verifying CMS SignedData
   objects (for compatibility with objects produced by implementations
   conforming to [RFC6485]).

3.  Asymmetric Key Pair Formats

   The RSA key pairs used to compute the signatures MUST have a 2048-bit
   modulus and a public exponent (e) of 65,537.

3.1.  Public Key Format

   The subject's public key is included in subjectPublicKeyInfo
   [RFC5280].  It has two sub-fields: algorithm and subjectPublicKey.
   The values for the structures and their sub-structures follow:

   algorithm (which is an AlgorithmIdentifier type):
      The object identifier for RSA PKCS #1 v1.5 with SHA-256 MUST be
      used in the algorithm field, as specified in Section 5 of
      [RFC4055].  The value for the associated parameters from that
      clause MUST also be used for the parameters field.

   subjectPublicKey:
      RSAPublicKey MUST be used to encode the certificate's
      subjectPublicKey field, as specified in [RFC4055].

3.2.  Private Key Format

   Local policy determines the private key format.

4.  Signature Format

   The structure for the certificate's signature field is as specified
   in Section 1.2 of [RFC4055].  The structure for the signature field
   in the CMS SignedData's SignerInfos is as specified in [RFC5652].

5.  Additional Requirements

   It is anticipated that the RPKI will require the adoption of updated
   key sizes and a different set of signature and hash algorithms over
   time, in order to maintain an acceptable level of cryptographic
   security to protect the integrity of signed products in the RPKI.
   This profile should be replaced to specify such future requirements,
   as and when appropriate.

   The procedures to implement such a transition of key sizes and
   algorithms are specified in [RFC6916].

6.  Security Considerations

   The Security Considerations of [RFC4055], [RFC5280], and [RFC6487]
   apply to certificates and CRLs.  The Security Considerations of
   [RFC2986], [RFC4211], and [RFC6487] apply to certification requests.
   The Security Considerations of [RFC5754] apply to CMS signed objects.
   No new security threats are introduced as a result of this
   specification.

7.  Changes Applied to RFC 6485

   This update includes a slight technical change to [RFC6485] that is
   considered to be outside the limited scope of an erratum.  The
   document update process has included other errata and also corrected
   a number of nits.

   Section 2 of [RFC6485] specified sha256WithRSAEncryption as the OID
   to use for the SignerInfo signatureAlgorithm field in CMS
   SignedObjects.  However, existing implementations use the
   rsaEncryption OID for this field.  (Support for rsaEncryption in
   third-party cryptographic libraries is better than
   sha256WithRSAEncryption, perhaps because [RFC3370] says that support
   for rsaEncryption is required, while support for OIDs that specify
   both RSA and a digest algorithm is optional.)

   Rather than force existing implementations to switch to
   sha256WithRSAEncryption, this document was changed to follow existing
   practice.  This does not represent a cryptographic algorithm change,
   just an identifier change.  (Unlike certificates, CRLs, and
   certification requests, CMS signed objects have a separate algorithm
   identifier field for the hash (digest) algorithm, and that field is
   already required to contain the id-sha256 OID per Section 2.)

   To avoid compatibility problems, RPs are still required to accept
   sha256WithRSAEncryption if encountered.

   Other changes include:

      *  Minor wording and typo fixes.

      *  Corrections to references ([RFC5652] instead of [RFC3370],
         [RFC3447] instead of [RFC4055]).

      *  Additional citations included in the Introduction.

      *  Correction to the CRMF POPOSigningKey field that is mentioned
         in Section 2 (algorithmIdentifier instead of signature).

      *  Inclusion of certification requests in mentions of
         certificates, CRLs, and CMS signed objects.

      *  Replacement of text in Section 5 with a pointer to the
         procedures specified in [RFC6916] (algorithm agility).

      *  Replacement of "signed object" with "CMS signed object"
         everywhere.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              DOI 10.17487/RFC2986, November 2000,
              <http://www.rfc-editor.org/info/rfc2986>.

   [RFC3370]  Housley, R., "Cryptographic Message Syntax (CMS)
              Algorithms", RFC 3370, DOI 10.17487/RFC3370, August 2002,
              <http://www.rfc-editor.org/info/rfc3370>.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, DOI 10.17487/RFC3447, February
              2003, <http://www.rfc-editor.org/info/rfc3447>.

   [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,
              DOI 10.17487/RFC4055, June 2005,
              <http://www.rfc-editor.org/info/rfc4055>.

   [RFC4211]  Schaad, J., "Internet X.509 Public Key Infrastructure
              Certificate Request Message Format (CRMF)", RFC 4211,
              DOI 10.17487/RFC4211, September 2005,
              <http://www.rfc-editor.org/info/rfc4211>.

   [RFC5280]  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, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <http://www.rfc-editor.org/info/rfc5652>.

   [RFC5754]  Turner, S., "Using SHA2 Algorithms with Cryptographic
              Message Syntax", RFC 5754, DOI 10.17487/RFC5754, January
              2010, <http://www.rfc-editor.org/info/rfc5754>.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
              February 2012, <http://www.rfc-editor.org/info/rfc6480>.

   [RFC6484]  Kent, S., Kong, D., Seo, K., and R. Watro, "Certificate
              Policy (CP) for the Resource Public Key Infrastructure
              (RPKI)", BCP 173, RFC 6484, DOI 10.17487/RFC6484, February
              2012, <http://www.rfc-editor.org/info/rfc6484>.

   [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
              X.509 PKIX Resource Certificates", RFC 6487,
              DOI 10.17487/RFC6487, February 2012,
              <http://www.rfc-editor.org/info/rfc6487>.

   [RFC6488]  Lepinski, M., Chi, A., and S. Kent, "Signed Object
              Template for the Resource Public Key Infrastructure
              (RPKI)", RFC 6488, DOI 10.17487/RFC6488, February 2012,
              <http://www.rfc-editor.org/info/rfc6488>.

   [SHS]      National Institute of Standards and Technology (NIST),
              "FIPS Publication 180-3: Secure Hash Standard", FIPS
              Publication 180-3, October 2008.

8.2.  Informative References

   [RFC6482]  Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
              Origin Authorizations (ROAs)", RFC 6482,
              DOI 10.17487/RFC6482, February 2012,
              <http://www.rfc-editor.org/info/rfc6482>.

   [RFC6485]  Huston, G., "The Profile for Algorithms and Key Sizes for
              Use in the Resource Public Key Infrastructure (RPKI)",
              RFC 6485, DOI 10.17487/RFC6485, February 2012,
              <http://www.rfc-editor.org/info/rfc6485>.

   [RFC6486]  Austein, R., Huston, G., Kent, S., and M. Lepinski,
              "Manifests for the Resource Public Key Infrastructure
              (RPKI)", RFC 6486, DOI 10.17487/RFC6486, February 2012,
              <http://www.rfc-editor.org/info/rfc6486>.

   [RFC6916]  Gagliano, R., Kent, S., and S. Turner, "Algorithm Agility
              Procedure for the Resource Public Key Infrastructure
              (RPKI)", BCP 182, RFC 6916, DOI 10.17487/RFC6916, April
              2013, <http://www.rfc-editor.org/info/rfc6916>.

Acknowledgments

   The authors acknowledge the reuse in this document of material
   originally contained in working drafts of the RPKI Certificate Policy
   [RFC6484] and resource certificate profile [RFC6487] documents.  The
   coauthors of these two documents -- namely, Stephen Kent, Derrick
   Kong, Karen Seo, Ronald Watro, George Michaelson, and Robert Loomans
   -- are acknowledged, with thanks.  The constraint on key size noted
   in this profile is the outcome of comments from Stephen Kent and
   review comments from David Cooper.  Sean Turner has provided
   additional review input to this document.

   Andrew Chi and David Mandelberg discovered the issue addressed in
   this replacement of [RFC6485], and the changes in this updated
   specification reflect the outcome of a discussion between Rob Austein
   and Matt Lepinski on the SIDR Working group mailing list.  Richard
   Hansen contributed a significant number of suggestions that have been
   incorporated into this document.

Authors' Addresses

   Geoff Huston
   APNIC

   Email: gih@apnic.net


   George Michaelson (editor)
   APNIC

   Email: ggm@apnic.net