RFC7935
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.
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Contents
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.
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.
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).
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.
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.
Private Key Format
Local policy determines the private key format.
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.
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.
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.
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.
References
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.
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: [email protected]
George Michaelson (editor) APNIC
Email: [email protected]
