| Network Working Group | S. Josefsson |
| Internet-Draft | SJD AB |
| Intended status: Standards Track | J. Schaad |
| Expires: May 27, 2017 | August Cellars |
| November 23, 2016 |
Algorithm Identifiers for Ed25519, Ed25519ph, Ed448, Ed448ph, X25519 and X448 for use in the Internet X.509 Public Key Infrastructure
draft-ietf-curdle-pkix-03
This document specifies algorithm identifiers and ASN.1 encoding formats for Elliptic Curve constructs using the Curve25519 and Curve448 curves. The signature algorithms covered are Ed25519, Ed25519ph, Ed448 and Ed448ph. The key agreement algorithm covered are X25519 and X448. The encoding for Public Key, Private Key and EdDSA digital signature structures is provided.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 27, 2017.
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.
In [RFC7748], the elliptic curves Curve25519 and Curve448 are described. They are designed with performance and security in mind. The curves may be used for Diffie-Hellman and Digital Signature operations.
[RFC7748] describes the operations on these curves for the Diffie-Hellman operation. A convention has developed that when these two curves are used with the Diffie-Hellman operation, they are referred to as X25519 and X448. This RFC defines the ASN.1 Object Identifiers (OIDs) for the operations X25519 and X448 along with the parameters. The use of these OIDs is described for public and private keys.
In [I-D.irtf-cfrg-eddsa] the elliptic curve signature system Edwards-curve Digital Signature Algorithm (EdDSA) is described along with a recommendation for the use of the Curve25519 and Curve448. EdDSA has defined two modes, the PureEdDSA mode without pre-hashing, and the HashEdDSA mode with pre-hashing. The Ed25519ph and Ed448ph algorithm definitions specify the one-way hash function that is used for pre-hashing. The convention used for identifying the algorithm/curve combinations are to use the Ed25519 and Ed448 for the PureEdDSA mode, with Ed25519ph and Ed448ph for the HashEdDSA mode. The use of the OIDs is described for public keys, private keys and signatures.
[I-D.irtf-cfrg-eddsa] additionally defined the concept of a context. Contexts can be used to differentiate signatures generated for different purposes with the same key. The use of contexts is not defined in this document for the following reasons:
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].
Certificates conforming to [RFC5280] can convey a public key for any public key algorithm. The certificate indicates the algorithm through an algorithm identifier. This algorithm identifier is an OID and optionally associated parameters.
The AlgorithmIdentifier type, which is included for convenience, is defined as follows:
AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL
}
The fields in AlgorithmIdentifier have the following meanings:
In this document we defined six new OIDs for identifying the different curve/algorithm pairs. The curves being Curve25519 and Curve448. The algorithms being ECDH, EdDSA in pure mode and EdDSA in pre-hash mode. For all of the OIDs, the parameters MUST be absent. Regardless of the defect in the original 1997 syntax, implementations MUST NOT accept a parameters value of NULL.
The same algorithm identifiers are used for identifying a public key, identifying a private key and identifying a signature (for the four EdDSA related OIDs). Additional encoding information is provided below for each of these locations.
id-X25519 OBJECT IDENTIFIER ::= { 1 3 101 110 }
id-X448 OBJECT IDENTIFIER ::= { 1 3 101 111 }
id-Ed25519 OBJECT IDENTIFIER ::= { 1 3 101 112 }
id-Ed448 OBJECT IDENTIFIER ::= { 1 3 101 113 }
id-Ed25519ph OBJECT IDENTIFIER ::= { 1 3 101 114 }
id-Ed448ph OBJECT IDENTIFIER ::= { 1 3 101 115 }
In the X.509 certificate, the subjectPublicKeyInfo field has the SubjectPublicKeyInfo type, which has the following ASN.1 syntax:
SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING
}
The fields in SubjectPublicKeyInfo have the following meanings:
Both [RFC7748] and [I-D.irtf-cfrg-eddsa] define the public key value as being a byte string. It should be noted that the public key is computed differently for each of these documents, thus the same private key will not produce the same public key.
The following is an example of a public key encoded using the textual encoding defined in [RFC7468].
-----BEGIN PUBLIC KEY----- MCowBQYDK2VwAyEAGb9ECWmEzf6FQbrBZ9w7lshQhqowtrbLDFw4rXAxZmE= -----END PUBLIC KEY-----
The intended application for the key is indicated in the keyUsage certificate extension.
If the keyUsage extension is present in a certificate that indicates id-X25119 or id-X448 in SubjectPublicKeyInfo, then the following MUST be present:
keyAgreement;
one of the following MAY also be present:
encipherOnly; or
decipherOnly.
If the keyUsage extension is present in an end-entity certificate that indicates id-EdDSA25519, id-EdDSA25519ph, id-EdDSA448 or id-EdDSA448ph , then the keyUsage extension MUST contain one or both of the following values:
nonRepudiation; and
digitalSignature.
If the keyUsage extension is present in a certification authority certificate that indicates id-EdDSA25519 or id-EdDSA448, then the keyUsage extension MUST contain one or more of the following values:
nonRepudiation;
digitalSignature;
keyCertSign; and
cRLSign.
CAs MUST NOT use the pre-hash versions of the EdDSA algorithms for the creation of certificates or CRLs. This is implied by the fact that those algorithms are not listed in the previous paragraph. Additionally OCSP responders SHOULD NOT use the pre-hash versions of the EdDSA algorithms when generating OCSP responses. No restriction is placed on generation of OCSP requests.
AAs MUST NOT use the pre-hash versions of the EdDSA algorithms for the creation of attribute certificates or attribute CRLs [RFC5755].
The decision to require the use of pure mode balances the higher security of having a single failure point againist the possibility that constrained devices, such as Hardware Security Modules (HSMs), may be unable to check signatures on CRLs due to the amount of memory required to hold the entire CRL in memory at one time. This concern can be addressed by CAs using CRL distribution points, combined with segmenting the certificates issued so that the length of any segmented CRL is not "too long" evenif a large percentage of the certificates are revoked. The defintion of "too long" is going to be highly dependent on what constrained device is being used, it can be on the order of single or low double digit kilobytes.
Signatures can be placed in a number of different ASN.1 structures. The top level structure for a certificate is given below as being illustrative of how signatures are frequently encoded with an algorithm identifier and a location for the signature.
Certificate ::= SEQUENCE {
tbsCertificate TBSCertificate,
signatureAlgorithm AlgorithmIdentifier,
signatureValue BIT STRING }
The same algorithm identifiers are used for signatures as are used for public keys. When used to identify signature algorithms, the parameters MUST be absent.
The data to be signed is prepared for EdDSA. Then, a private key operation is performed to generate the signature value. This value is the opaque value ENC(R) || ENC(S) described in section 3.3 of [I-D.irtf-cfrg-eddsa]. The octet string representing the signature is encoded directly in the BIT STRING without adding any additional ASN.1 wrapping. For the Certificate structure, the signature value is wrapped in the 'signatureValue' BIT STRING field.
When the pre-hash versions of the EdDSA signature algorithms are used, the hash function used for the pre-hash is defined by the algorithm. This means that the pre-hash function is implicitly included in the algorithm identifier rather than being explicit as done in [RFC3279].
Asymmetric Key Packages [RFC5958] describes how encode a private key in a structure that both identifies what algorithm the private key is for, but allows for the public key and additional attributes about the key to be included as well. For illustration, the ASN.1 structure OneAsymmetricKey is replicated below. The algorithm specific details of how a private key is encoded is left for the document describing the algorithm itself.
OneAsymmetricKey ::= SEQUENCE {
version Version,
privateKeyAlgorithm PrivateKeyAlgorithmIdentifier,
privateKey PrivateKey,
attributes [0] Attributes OPTIONAL,
...,
[[2: publicKey [1] PublicKey OPTIONAL ]],
...
}
PrivateKey ::= OCTET STRING
PublicKey ::= OCTET STRING
For the keys defined in this document, the private key is always an opaque byte sequence. The ASN.1 type EdPrivateKey is defined in this document to hold the byte sequence. Thus when encoding a OneAsymmetricKey object, the private key is wrapped in an EdPrivateKey object and then placed in the 'privateKey' field.
EdPrivateKey ::= OCTET STRING
To encode a EdDSA, X25519 or X448 private key, the "privateKey" field will hold the encoded private key. The "privateKeyAlgorithm" field uses the AlgorithmIdentifier structure. The structure is encoded as defined above. If present, the "publicKey" field will hold the encoded key as defined in [RFC7748] and [I-D.irtf-cfrg-eddsa]. public key.
The following is an example of a private key encoded using the textual encoding defined in [RFC7468].
-----BEGIN PRIVATE KEY----- MC4CAQAwBQYDK2VwBCIEINTuctv5E1hK1bbY8fdp+K06/nwoy/HU++CXqI9EdVhC -----END PRIVATE KEY-----
For the purpose of consistent cross-implementation naming this section establishes human readable names for the algorithms specified in this document. Implementations SHOULD use these names when referring to the algorithms. If there is a strong reason to deviate from these names -- for example, if the implementation has a different naming convention and wants to maintain internal consistency -- it is encouraged to deviate as little as possible from the names given here.
Use the string "ECDH" when referring to a public key of type X25519 or X448 when the curve is not known or relevant.
When the curve is known, use the more specific string of X25519 or X448.
Use the string "EdDSA" when referring to a signing public key or signature when the curve is not known or relevant.
When the curve is known, use a more specific string. For the id-EdDSA25519 value use the string "Ed25519". For the id-EdDSA25519ph value use the string "Ed25519ph". For id-EdDSA448 use "Ed448". For id-EdDSA448ph use "Ed448ph".
For reference purposes, the ASN.1 syntax is presented as an ASN.1 module here.
-- ASN.1 Module
Safecurves-pkix-0 {1 3 101 120}
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
IMPORTS
SIGNATURE-ALGORITHM, KEY-AGREE, PUBLIC-KEY, KEY-WRAP,
KeyUsage, AlgorithmIdentifier
FROM AlgorithmInformation-2009
{iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0)
id-mod-algorithmInformation-02(58)}
mda-sha512
FROM PKIX1-PSS-OAEP-Algorithms-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-rsa-pkalgs-02(54) }
kwa-aes128-wrap, kwa-aes256-wrap
FROM CMSAesRsaesOaep-2009
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) id-mod-cms-aes-02(38) }
;
id-edwards-curve-algs OBJECT IDENTIFIER ::= { 1 3 101 }
id-X25519 OBJECT IDENTIFIER ::= { id-edwards-curve-algs 110 }
id-X448 OBJECT IDENTIFIER ::= { id-edwards-curve-algs 111 }
id-EdDSA25519 OBJECT IDENTIFIER ::= { id-edwards-curve-algs 112 }
id-EdDSA25519-ph OBJECT IDENTIFIER ::= { id-edwards-curve-algs 114 }
id-EdDSA448 OBJECT IDENTIFIER ::= { id-edwards-curve-algs 113 }
id-EdDSA448-ph OBJECT IDENTIFIER ::= { id-edwards-curve-algs 115 }
sa-EdDSA25519 SIGNATURE-ALGORITHM ::= {
IDENTIFIER id-EdDSA25519
PARAMS ARE absent
PUBLIC-KEYS {pk-EdDSA25519}
SMIME-CAPS { IDENTIFIED BY id-EdDSA25519 }
}
pk-EdDSA25519 PUBLIC-KEY ::= {
IDENTIFIER id-EdDSA25519
-- KEY no ASN.1 wrapping --
PARAMS ARE absent
CERT-KEY-USAGE {digitalSignature, nonRepudiation,
keyCertSign, cRLSign}
PRIVATE-KEY EdPrivateKey
}
sa-EdDSA25519-ph SIGNATURE-ALGORITHM ::= {
IDENTIFIER id-EdDSA25519-ph
PARAMS ARE absent
HASHES { mda-sha512 }
PUBLIC-KEYS {pk-EdDSA25519-ph}
SMIME-CAPS { IDENTIFIED BY id-EdDSA25519-ph }
}
pk-EdDSA25519-ph PUBLIC-KEY ::= {
IDENTIFIER id-EdDSA25519-ph
-- KEY no ASN.1 wrapping --
PARAMS ARE absent
CERT-KEY-USAGE {digitalSignature, nonRepudiation}
PRIVATE-KEY EdPrivateKey
}
kaa-X25519 KEY-AGREE ::= {
IDENTIFIER id-X25519
PARAMS ARE absent
PUBLIC-KEYS {pk-X25519}
UKM -- TYPE no ASN.1 wrapping -- ARE preferredPresent
SMIME-CAPS {
TYPE AlgorithmIdentifier{KEY-WRAP, {KeyWrapAlgorithms}}
IDENTIFIED BY id-X25519 }
}
pk-X25519 PUBLIC-KEY ::= {
IDENTIFIER id-X25519
-- KEY no ASN.1 wrapping --
PARAMS ARE absent
CERT-KEY-USAGE { keyAgreement }
PRIVATE-KEY EdPrivateKey
}
KeyWrapAlgorithms KEY-WRAP ::= {
kwa-aes128-wrap | kwa-aes256-wrap,
...
}
kaa-X488 KEY-AGREE ::= {
IDENTIFIER id-X448
PARAMS ARE absent
PUBLIC-KEYS {pk-X448}
UKM -- TYPE no ASN.1 wrapping -- ARE preferredPresent
SMIME-CAPS {
TYPE AlgorithmIdentifier{KEY-WRAP, {KeyWrapAlgorithms}}
IDENTIFIED BY id-X448 }
}
pk-X448 PUBLIC-KEY ::= {
IDENTIFIER id-X448
-- KEY no ASN.1 wrapping --
PARAMS ARE absent
CERT-KEY-USAGE { keyAgreement }
PRIVATE-KEY EdPrivateKey
}
EdPrivateKey ::= OCTET STRING
END
This section contains illustrations of EdDSA public keys and certificates, illustrating parameter choices.
An example of a Ed25519 public key:
Public Key Information:
Public Key Algorithm: EdDSA25519
Algorithm Security Level: High
Public Key Usage:
Public Key ID: 9b1f5eeded043385e4f7bc623c5975b90bc8bb3b
-----BEGIN PUBLIC KEY-----
MCowBQYDK2VwAyEAGb9ECWmEzf6FQbrBZ9w7lshQhqowtrbLDFw4rXAxZmE=
-----END PUBLIC KEY-----
An example of a self issued PKIX certificate using Ed25519 to sign a X25519 public key would be:
0 300: SEQUENCE {
4 223: SEQUENCE {
7 3: [0] {
9 1: INTEGER 2
: }
12 8: INTEGER 56 01 47 4A 2A 8D C3 30
22 5: SEQUENCE {
24 3: OBJECT IDENTIFIER
: EdDSA 25519 signature algorithm { 1 3 101 112 }
: }
29 25: SEQUENCE {
31 23: SET {
33 21: SEQUENCE {
35 3: OBJECT IDENTIFIER commonName (2 5 4 3)
40 14: UTF8String 'IETF Test Demo'
: }
: }
: }
56 30: SEQUENCE {
58 13: UTCTime 01/08/2016 12:19:24 GMT
73 13: UTCTime 31/12/2040 23:59:59 GMT
: }
88 25: SEQUENCE {
90 23: SET {
92 21: SEQUENCE {
94 3: OBJECT IDENTIFIER commonName (2 5 4 3)
99 14: UTF8String 'IETF Test Demo'
: }
: }
: }
115 42: SEQUENCE {
117 5: SEQUENCE {
119 3: OBJECT IDENTIFIER
: ECDH 25519 key agreement { 1 3 101 110 }
: }
124 33: BIT STRING
: 85 20 F0 09 89 30 A7 54 74 8B 7D DC B4 3E F7 5A
: 0D BF 3A 0D 26 38 1A F4 EB A4 A9 8E AA 9B 4E 6A
: }
159 69: [3] {
161 67: SEQUENCE {
163 15: SEQUENCE {
165 3: OBJECT IDENTIFIER basicConstraints (2 5 29 19)
170 1: BOOLEAN TRUE
173 5: OCTET STRING, encapsulates {
175 3: SEQUENCE {
177 1: BOOLEAN FALSE
: }
: }
: }
180 14: SEQUENCE {
182 3: OBJECT IDENTIFIER keyUsage (2 5 29 15)
187 1: BOOLEAN FALSE
190 4: OCTET STRING, encapsulates {
192 2: BIT STRING 3 unused bits
: '10000'B (bit 4)
: }
: }
196 32: SEQUENCE {
198 3: OBJECT IDENTIFIER subjectKeyIdentifier (2 5 29 14)
203 1: BOOLEAN FALSE
206 22: OCTET STRING, encapsulates {
208 20: OCTET STRING
: 9B 1F 5E ED ED 04 33 85 E4 F7 BC 62 3C 59 75 B9
: 0B C8 BB 3B
: }
: }
: }
: }
: }
230 5: SEQUENCE {
232 3: OBJECT IDENTIFIER
: EdDSA 25519 signature algorithm { 1 3 101 112 }
: }
237 65: BIT STRING
: AF 23 01 FE DD C9 E6 FF C1 CC A7 3D 74 D6 48 A4
: 39 80 82 CD DB 69 B1 4E 4D 06 EC F8 1A 25 CE 50
: D4 C2 C3 EB 74 6C 4E DD 83 46 85 6E C8 6F 3D CE
: 1A 18 65 C5 7A C2 7B 50 A0 C3 50 07 F5 E7 D9 07
: }
-----BEGIN CERTIFICATE-----
MIIBLDCB36ADAgECAghWAUdKKo3DMDAFBgMrZXAwGTEXMBUGA1UEAwwOSUVURiBUZX
N0IERlbW8wHhcNMTYwODAxMTIxOTI0WhcNNDAxMjMxMjM1OTU5WjAZMRcwFQYDVQQD
DA5JRVRGIFRlc3QgRGVtbzAqMAUGAytlbgMhAIUg8AmJMKdUdIt93LQ+91oNvzoNJj
ga9OukqY6qm05qo0UwQzAPBgNVHRMBAf8EBTADAQEAMA4GA1UdDwEBAAQEAwIDCDAg
BgNVHQ4BAQAEFgQUmx9e7e0EM4Xk97xiPFl1uQvIuzswBQYDK2VwA0EAryMB/t3J5v
/BzKc9dNZIpDmAgs3babFOTQbs+BolzlDUwsPrdGxO3YNGhW7Ibz3OGhhlxXrCe1Cg
w1AH9efZBw==
-----END CERTIFICATE-----
An example of an Ed25519 private key:
-----BEGIN PRIVATE KEY----- MC4CAQAwBQYDK2VwBCIEINTuctv5E1hK1bbY8fdp+K06/nwoy/HU++CXqI9EdVhC -----END PRIVATE KEY-----
Text and/or inspiration were drawn from [RFC5280], [RFC3279], [RFC4055], [RFC5480], and [RFC5639].
The following people discussed the document and provided feedback: Klaus Hartke, Ilari Liusvaara, Erwann Abalea, Rick Andrews, Rob Stradling, James Manger, Nikos Mavrogiannopoulos, Russ Housley, David Benjamin, and Alex Wilson.
A big thank you to Symantec for kindly donating the OIDs used in this draft.
None.
The security considerations of [RFC5280], [RFC7748], and [I-D.irtf-cfrg-eddsa] apply accordingly.
The procedures for going from a private key to a public key is different for when used with Diffie-Helman and when used with Edwards Signatures. This means that the same public key cannot be used for both ECDH and EdDSA.
In the original design of Ed25519 signatures, there was a known attack between the pure and the pre-hash version of the signatures. This has since been corrected in the final version of the design. The initial problem meant that there was a known attack, and therefore a known reason to forbid the use of Ed25519 keys with the Ed25519ph signature scheme and visa versa. With the change in the design this attack has been prevented. This does not mean that the same Ed25519 key should be used with both schemes, there still may be attacks where collisions can be found. For this reason, the same keys are not to be used for the pure and pre-hash versions of the scheme. This applies to both curve 25519 and curve 448.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [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. |
| [RFC5480] | Turner, S., Brown, D., Yiu, K., Housley, R. and T. Polk, "Elliptic Curve Cryptography Subject Public Key Information", RFC 5480, DOI 10.17487/RFC5480, March 2009. |
| [RFC7748] | Langley, A., Hamburg, M. and S. Turner, "Elliptic Curves for Security", RFC 7748, DOI 10.17487/RFC7748, January 2016. |
| [I-D.irtf-cfrg-eddsa] | Josefsson, S. and I. Liusvaara, "Edwards-curve Digital Signature Algorithm (EdDSA)", Internet-Draft draft-irtf-cfrg-eddsa-08, August 2016. |
| [RFC5958] | Turner, S., "Asymmetric Key Packages", RFC 5958, DOI 10.17487/RFC5958, August 2010. |
| [RFC3279] | Bassham, L., Polk, W. and R. Housley, "Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3279, DOI 10.17487/RFC3279, April 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, DOI 10.17487/RFC4055, June 2005. |
| [RFC5639] | Lochter, M. and J. Merkle, "Elliptic Curve Cryptography (ECC) Brainpool Standard Curves and Curve Generation", RFC 5639, DOI 10.17487/RFC5639, March 2010. |
| [RFC5755] | Farrell, S., Housley, R. and S. Turner, "An Internet Attribute Certificate Profile for Authorization", RFC 5755, DOI 10.17487/RFC5755, January 2010. |
| [RFC7468] | Josefsson, S. and S. Leonard, "Textual Encodings of PKIX, PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468, April 2015. |