Internet Engineering Task Force (IETF)                         G. Huston
Request for Comments: 6485                                         APNIC
Category: Standards Track                                  February 2012
ISSN: 2070-1721


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

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, and signed objects 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 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/rfc6485.

Copyright Notice

   Copyright (c) 2012 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
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   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

   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) subscribers when
   they apply digital signatures to certificates, Certificate Revocation
   Lists (CRLs), and signed objects (e.g., Route Origin Authorizations
   (ROAs) and manifests).  Relying parties (RPs) also use the algorithms
   defined in this document to verify RPKI subscribers' digital
   signatures [RFC6480].

   This document is referenced by other RPKI profiles and
   specifications, including the RPKI Certificate Policy (CP) [RFC6484],
   the RPKI Certificate Profile [RFC6487], the SIDR 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, and signed
         objects is RSA Public-Key Cryptography Standards (PKCS) #1
         Version 1.5 (sometimes referred to as "RSASSA-PKCS1-v1_5") from
         Section 5 of [RFC4055].

      *  The hashing algorithm used in certificates, CRLs, and signed
         objects is SHA-256 [SHS].  The hashing algorithm is not
         identified by itself when used in certificates and CRLs, as
         they are combined with the digital signature algorithm (see
         below).

         When used in the Cryptographic Message Syntax (CMS) SignedData,
         the hash algorithm (in this case, the hash algorithm is
         sometimes called a message digest algorithm) is identified by
         itself.  For CMS SignedData, the object identifier and
         parameters for SHA-256 (as defined in [RFC5754]) MUST be used

         when populating the digestAlgorithms and digestAlgorithm
         fields.

         NOTE: The exception to the above hashing algorithm is the use
         of SHA-1 [SHS] when Certification Authorities (CAs) generate
         authority and subject key identifiers [RFC6487].

   When used to generate and verify digital signatures the hash and
   digital signature algorithms are referred 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.

   Locations for this OID are as follows:

      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 CMS SignedData, the OID appears in each SignerInfo
      signatureAlgoithm field [RFC3370] using the OID from above; and,

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

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 CMS SignedData's
   signature field is as specified in [RFC3370].

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.

   CAs and RPs SHOULD be capable of supporting a transition to allow for
   the phased introduction of additional encryption algorithms and key
   specifications, and also accommodate the orderly deprecation of
   previously specified algorithms and keys.  Accordingly, CAs and RPs
   SHOULD be capable of supporting multiple RPKI algorithm and key
   profiles simultaneously within the scope of such anticipated
   transitions.  The recommended procedures to implement such a
   transition of key sizes and algorithms is not specified in this
   document.

6.  Security Considerations

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

7.  Acknowledgments

   The author acknowledges the reuse in this document of material
   originally contained in working drafts of the RPKI Certificate Policy
   [RFC6484] and the resource certificate profile [RFC6487] documents.
   The co-authors 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.

9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              November 2000.

   [RFC3370]  Housley, R., "Cryptographic Message Syntax (CMS)
              Algorithms", RFC 3370, August 2002.

   [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.

   [RFC4211]  Schaad, J., "Internet X.509 Public Key Infrastructure
              Certificate Request Message Format (CRMF)", RFC 4211,
              September 2005.

   [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, May 2008.

   [RFC5754]  Turner, S., "Using SHA2 Algorithms with Cryptographic
              Message Syntax", RFC 5754, January 2010.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, February 2012.

   [RFC6484]  Kent, S., Kong, D., Seo, K., and R. Watro, "Certificate
              Policy (CP) for the Resource Public Key Infrastructure
              (RPKI)", BCP 173, RFC 6484, February 2012.

   [RFC6487]  Husotn, G., Michaelson, G., and R. Loomans, "A Profile for
              X.509 PKIX Resource Certificates", RFC 6487, February
              2012.

   [RFC6488]  Lepinski, M., Chi, A., and S. Kent, "Signed Object
              Template for the Resource Public Key Infrastructure
              (RPKI)", RFC 6488, February 2012.

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

Author's Address

   Geoff Huston
   APNIC

   EMail: gih@apnic.net