Internet Engineering Task Force (IETF) G. Huston
Request for Comments: 7935 G. Michaelson, Ed.
Obsoletes: 6485 APNIC
Category: Standards Track August 2016
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
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
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
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].
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
* The hashing algorithm used in certificates, CRLs, CMS signed
objects and certification requests is SHA-256 [SHS] (see note
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
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
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.
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
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"
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.
George Michaelson (editor)