RPKI Algorithms: The Profile for Algorithms and Key Sizes for Use in the Resource Public Key Infrastructure
The one agreed set of signature and hash algorithms and key sizes that every RPKI participant uses.
Huston, G. and G. Michaelson, Ed., "The Profile for Algorithms and Key Sizes for Use in the Resource Public Key Infrastructure", RFC 7935, DOI 10.17487/RFC7935, August 2016, <https://www.rfc-editor.org/info/rfc7935>.
@misc{rfc7935,
series = {Request for Comments},
number = 7935,
howpublished = {RFC 7935},
publisher = {RFC Editor},
doi = {10.17487/RFC7935},
url = {https://www.rfc-editor.org/info/rfc7935},
author = {G. Huston and G. Michaelson},
title = {{The Profile for Algorithms and Key Sizes for Use in the Resource Public Key Infrastructure}},
pagetotal = 9,
year = 2016,
month = aug,
} RFC text
Contents
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
(http://trustee.ietf.org/license-info) in effect on the date of
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
AI ELI5
On this page
§1Purpose of the Profile
This document sets four things used by Resource Public Key Infrastructure (RPKI) subscribers when they apply digital signatures: the signature algorithm and its parameters, the hash algorithm and its parameters, the public and private key formats, and the signature format.
They apply to certificates, Certificate Revocation Lists (CRLs), Cryptographic Message Syntax (CMS) signed objects such as Route Origin Authorizations (RFC 6482) and manifests (RFC 6486), and certification requests. Relying parties use the same algorithms to verify those signatures.
Other RPKI documents that used to point to RFC 6485 now point here, including the certificate policy, the certificate profile (RFC 6487), the architecture (RFC 6480) and the signed object template (RFC 6488).
Everyone who signs or checks these papers needs to use the same kind of pen and the same way of writing the signature, or the checks would not work.
§2The Two Algorithms
Two cryptographic algorithms are used. The signature algorithm is RSA PKCS #1 version 1.5 (also called RSASSA-PKCS1-v1_5), taken from RFC 3447. The hashing algorithm is SHA-256. The one exception is SHA-1, which CAs use when they generate authority and subject key identifiers.
In certificates, CRLs and certification requests, the hash and signature algorithms are named together as a single identifier. The object identifier sha256WithRSAEncryption from RFC 4055 MUST be used in those products.
CMS SignedData is different because it names the hash and the signature separately. The identifier for SHA-256 MUST be used for the digest algorithm fields, and the identifier for rsaEncryption MUST be used for the SignerInfo signatureAlgorithm field when generating objects. When verifying, implementations MUST accept either rsaEncryption or sha256WithRSAEncryption in that field, for compatibility with objects made under RFC 6485.
Everyone uses the same lock-and-key method and the same way of squishing a document into a short fingerprint. Some signed papers write down the two choices together, others write them separately.
| Product | How hash and signature are named |
|---|---|
| Certificates, CRLs, certification requests | Together: sha256WithRSAEncryption |
| CMS signed objects (generating) THIS RFC | Separately: SHA-256 digest plus rsaEncryption |
| CMS signed objects (verifying) | Accept rsaEncryption or sha256WithRSAEncryption |
§3Key Pairs and Signature Format
The RSA key pairs used to compute signatures MUST have a 2048-bit modulus and a public exponent of 65,537.
The public key goes in the subjectPublicKeyInfo structure from RFC 5280. Its algorithm field MUST carry the object identifier for RSA PKCS #1 v1.5 with SHA-256 together with the parameters value from RFC 4055, and the key itself MUST be encoded as an RSAPublicKey. The private key format is left to local policy.
A certificate's signature field follows RFC 4055, and the signature in CMS SignerInfos follows RFC 5652.
The key has a required size, so it is hard to guess. How you store your own secret key at home is up to you, but the public part must be written down in one agreed way.
§6Security and Future Change
The RFC adds no new security text of its own. It points to the security considerations of RFC 4055, RFC 5280 and RFC 6487 for certificates and CRLs, to those of RFC 2986, RFC 4211 and RFC 6487 for certification requests, and to those of RFC 5754 for CMS signed objects. It states that no new security threats are introduced by this specification.
The profile expects to change. Key sizes and algorithms will probably need updating over time to keep an acceptable level of cryptographic security, and this profile should be replaced when that happens. The transition procedures are specified in RFC 6916.
Locks get weaker as burglars get better tools, so the rules say they will be swapped for stronger ones later, using a plan written in another document.
§7What Changed from RFC 6485
The main change is technical. RFC 6485 required sha256WithRSAEncryption in the SignerInfo signatureAlgorithm field of CMS signed objects, but existing implementations used rsaEncryption. The RFC says support for rsaEncryption in third-party libraries is better, perhaps because RFC 3370 requires it while identifiers that combine RSA and a digest are optional.
Rather than make implementations switch, this document follows existing practice. It calls this an identifier change, not a cryptographic algorithm change, since CMS has a separate digest field that already had to hold the SHA-256 identifier. Relying parties must still accept sha256WithRSAEncryption if they see it.
Other changes include wording and typo fixes, corrected references, added citations, a corrected CRMF field name, mentions of certification requests alongside the other products, and a pointer to RFC 6916 in place of the old text on algorithm agility.
The old rule asked for a name nobody was using. Instead of making everyone change, the rule was fixed to match what people already did, and the old name is still accepted.