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
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.
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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.
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].
Huston & Michaelson Standards Track [Page 3]
RFC 7935 RPKI Algorithm Profile August 2016
* 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]).
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].
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].
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.
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.
[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>.
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.