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Versions: (draft-ietf-curdle-pkix-newcurves) 00 01 02 03 04 05 06

Network Working Group                                       S. Josefsson
Internet-Draft                                                    SJD AB
Intended status: Standards Track                               J. Schaad
Expires: March 16, 2018                                   August Cellars
                                                      September 12, 2017


Algorithm Identifiers for Ed25519, Ed448, X25519 and X448 for use in the
                Internet X.509 Public Key Infrastructure
                       draft-ietf-curdle-pkix-06

Abstract

   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 and
   Ed448.  The key agreement algorithm covered are X25519 and X448.  The
   encoding for Public Key, Private Key and EdDSA digital signature
   structures is provided.

Status of This Memo

   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 https://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 March 16, 2018.

Copyright Notice

   Copyright (c) 2017 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
   (https://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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Terminology  . . . . . . . . . . . . . . . . . .   3
   3.  Curve25519 and Curve448 Algorithm Identifiers . . . . . . . .   3
   4.  Subject Public Key Fields . . . . . . . . . . . . . . . . . .   4
   5.  Key Usage Bits  . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  EdDSA Signatures  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Private Key Format  . . . . . . . . . . . . . . . . . . . . .   6
   8.  Human Readable Algorithm Names  . . . . . . . . . . . . . . .   8
   9.  ASN.1 Module  . . . . . . . . . . . . . . . . . . . . . . . .   8
   10. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Example Ed25519 Public Key . . . . . . . . . . . . . . .  10
     10.2.  Example X25519 Certificate . . . . . . . . . . . . . . .  11
     10.3.  Examples of Ed25519 Private Key  . . . . . . . . . . . .  13
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  14
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     14.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Appendix A.  Invalid Encodings  . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   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 [RFC8032] 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 convention used for identifying
   the algorithm/curve combinations are to use the Ed25519 and Ed448 for



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   the PureEdDSA mode.  The document does not provide the conventions
   needed for the pre-hash versions of the signature algorithm.  The use
   of the OIDs is described for public keys, private keys and
   signatures.

   [RFC8032] 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:

   o  The current implementations of Ed25519 do not support the use of
      contexts, thus if specified it will potentially delay the use of
      these algorithms further.

   o  The EdDSA algorithms are the only IETF algorithms that currently
      support the use of contexts, however there is a possibility that
      there will be confusion between which algorithms need have
      separate keys and which do not.  This may result in a decrease of
      security for those other algorithms.

   o  There are still on going discussions among the cryptographic
      community about how effective the use of contexts is for
      preventing attacks.

   o  There needs to be discussions about the correct way to identify
      when context strings are to be used.  It is not clear if different
      OIDs should be used for different contexts, or the OID should
      merely not that a context string needs to be provided.

2.  Requirements 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].

3.  Curve25519 and Curve448 Algorithm Identifiers

   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:







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   AlgorithmIdentifier  ::=  SEQUENCE  {
       algorithm   OBJECT IDENTIFIER,
       parameters  ANY DEFINED BY algorithm OPTIONAL
   }

   The fields in AlgorithmIdentifier have the following meanings:

   o  algorithm identifies the cryptographic algorithm with an object
      identifier.  This is one of the OIDs defined below.

   o  parameters, which are optional, are the associated parameters for
      the algorithm identifier in the algorithm field.  When the 1997
      syntax for AlgorithmIdentifier was initially defined, it omitted
      the OPTIONAL key word.  The optionality of the parameters field
      was later recovered via a defect report, but by then many people
      thought that the field was mandatory.  For this reason, a small
      number of implementations may still require the field to be
      present.

   In this document we defined four new OIDs for identifying the
   different curve/algorithm pairs.  The curves being curve25519 and
   curve448.  The algorithms being ECDH and EdDSA in pure 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 two
   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 }

4.  Subject Public Key Fields

   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:




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   o  algorithm is the algorithm identifier and parameters for the
      public key (see above).

   o  subjectPublicKey contains the byte stream of the public key.  The
      algorithms defined in this document always encode the public key
      as an exact multiple of 8-bits.

   Both [RFC7748] and [RFC8032] 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-----
   MCowBQYDK2VwAyEAGb9ECWmEzf6FQbrBZ9w7lshQhqowtrbLDFw4rXAxZuE=
   -----END PUBLIC KEY-----

5.  Key Usage Bits

   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-X25519 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-Ed25519 or id-Ed448, 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-Ed25519 or id-Ed448, then the keyUsage
   extension MUST contain one or more of the following values:






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          nonRepudiation;
          digitalSignature;
          keyCertSign; and
          cRLSign.

6.  EdDSA Signatures

   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
   [RFC8032].  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.

7.  Private Key Format

   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.













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   OneAsymmetricKey ::= SEQUENCE {
      version Version,
      privateKeyAlgorithm PrivateKeyAlgorithmIdentifier,
      privateKey PrivateKey,
      attributes [0] IMPLICIT Attributes OPTIONAL,
      ...,
      [[2: publicKey [1] IMPLICIT PublicKey OPTIONAL ]],
      ...
   }

   PrivateKey ::= OCTET STRING

   PublicKey ::= BIT STRING

   For the keys defined in this document, the private key is always an
   opaque byte sequence.  The ASN.1 type CurvePrivateKey is defined in
   this document to hold the byte sequence.  Thus when encoding a
   OneAsymmetricKey object, the private key is wrapped in an
   CurvePrivateKey object and wrapped by the OCTET STRING of the
   "privateKey" field.

   CurvePrivateKey ::= 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 [RFC8032].

   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-----

   The following example, in addition to encoding the private key,
   additionally has an attribute included as well as the public key.  As
   with the prior example, the textual encoding defined in [RFC7468] is
   used.

   -----BEGIN PRIVATE KEY-----
   MHICAQEwBQYDK2VwBCIEINTuctv5E1hK1bbY8fdp+K06/nwoy/HU++CXqI9EdVhC
   oB8wHQYKKoZIhvcNAQkJFDEPDA1DdXJkbGUgQ2hhaXJzgSEAGb9ECWmEzf6FQbrB
   Z9w7lshQhqowtrbLDFw4rXAxZuE=
   -----END PRIVATE KEY------





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   NOTE: There exist some private key import functions that have not
   picked up the new ASN.1 structure OneAsymmetricKey that is defined in
   [RFC7748].  This means that they will not accept a private key
   structure which contains the public key field.  This means a
   balancing act needs to be done between being able to do a consistency
   check on the key pair and widest ability to import the key.

8.  Human Readable Algorithm Names

   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-
   Ed25519 value use the string "Ed25519".  For id-Ed448 use "Ed448".

9.  ASN.1 Module

   For reference purposes, the ASN.1 syntax is presented as an ASN.1
   module here.

   -- ASN.1 Module

   Safecurves-pkix-0 -- TBD - IANA assigned module OID

   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)



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       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-Ed25519       OBJECT IDENTIFIER ::= { id-edwards-curve-algs 112 }
   id-Ed448         OBJECT IDENTIFIER ::= { id-edwards-curve-algs 113 }


    sa-Ed25519 SIGNATURE-ALGORITHM ::= {
       IDENTIFIER id-Ed25519
        PARAMS ARE absent
        PUBLIC-KEYS {pk-Ed25519}
        SMIME-CAPS { IDENTIFIED BY id-Ed25519 }
    }

    pk-Ed25519 PUBLIC-KEY ::= {
        IDENTIFIER id-Ed25519
        -- KEY no ASN.1 wrapping --
        PARAMS ARE absent
        CERT-KEY-USAGE {digitalSignature, nonRepudiation,
                        keyCertSign, cRLSign}
        PRIVATE-KEY CurvePrivateKey
    }

    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 }
    }



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    pk-X25519 PUBLIC-KEY ::= {
        IDENTIFIER id-X25519
        -- KEY no ASN.1 wrapping --
        PARAMS ARE absent
        CERT-KEY-USAGE { keyAgreement }
        PRIVATE-KEY CurvePrivateKey
    }

    KeyWrapAlgorithms KEY-WRAP ::= {
        kwa-aes128-wrap | kwa-aes256-wrap,
        ...
    }

    kaa-X448 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 CurvePrivateKey
    }

   CurvePrivateKey ::= OCTET STRING


   END

10.  Examples

   This section contains illustrations of EdDSA public keys and
   certificates, illustrating parameter choices.

10.1.  Example Ed25519 Public Key

   An example of a Ed25519 public key:







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         Public Key Information:
             Public Key Algorithm: Ed25519
             Algorithm Security Level: High

         Public Key Usage:

         Public Key ID: 9b1f5eeded043385e4f7bc623c5975b90bc8bb3b

         -----BEGIN PUBLIC KEY-----
         MCowBQYDK2VwAyEAGb9ECWmEzf6FQbrBZ9w7lshQhqowtrbLDFw4rXAxZuE=
         -----END PUBLIC KEY-----

10.2.  Example X25519 Certificate

   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
          :         Ed 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 {



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   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
          :       Ed 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



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          :   }

   -----BEGIN CERTIFICATE-----
   MIIBLDCB36ADAgECAghWAUdKKo3DMDAFBgMrZXAwGTEXMBUGA1UEAwwOSUVURiBUZX
   N0IERlbW8wHhcNMTYwODAxMTIxOTI0WhcNNDAxMjMxMjM1OTU5WjAZMRcwFQYDVQQD
   DA5JRVRGIFRlc3QgRGVtbzAqMAUGAytlbgMhAIUg8AmJMKdUdIt93LQ+91oNvzoNJj
   ga9OukqY6qm05qo0UwQzAPBgNVHRMBAf8EBTADAQEAMA4GA1UdDwEBAAQEAwIDCDAg
   BgNVHQ4BAQAEFgQUmx9e7e0EM4Xk97xiPFl1uQvIuzswBQYDK2VwA0EAryMB/t3J5v
   /BzKc9dNZIpDmAgs3babFOTQbs+BolzlDUwsPrdGxO3YNGhW7Ibz3OGhhlxXrCe1Cg
   w1AH9efZBw==
   -----END CERTIFICATE-----

10.3.  Examples of Ed25519 Private Key

   An example of an Ed25519 private key without the public key:

   -----BEGIN PRIVATE KEY-----
   MC4CAQAwBQYDK2VwBCIEINTuctv5E1hK1bbY8fdp+K06/nwoy/HU++CXqI9EdVhC
   -----END PRIVATE KEY-----

   The same item dumped as asn1 yields:

    0 30   46: SEQUENCE {
    2 02    1:   INTEGER 0
    5 30    5:   SEQUENCE {
    7 06    3:     OBJECT IDENTIFIER
             :       Ed 25519 signature algorithm { 1 3 101 112 }
             :     }
   12 04   34:   OCTET STRING
             :     04 20 D4 EE 72 DB F9 13 58 4A D5 B6 D8 F1 F7 69
             :     F8 AD 3A FE 7C 28 CB F1 D4 FB E0 97 A8 8F 44 75
             :     58 42
             :   }

   Note that the value of the private key is:

   D4 EE 72 DB F9 13 58 4A D5 B6 D8 F1 F7 69 F8 AD
   3A FE 7C 28 CB F1 D4 FB E0 97 A8 8F 44 75 58 42

   An example of the same Ed25519 private key encoded with an attribute
   and the public key:

   -----BEGIN PRIVATE KEY-----
   MHICAQEwBQYDK2VwBCIEINTuctv5E1hK1bbY8fdp+K06/nwoy/HU++CXqI9EdVhC
   oB8wHQYKKoZIhvcNAQkJFDEPDA1DdXJkbGUgQ2hhaXJzgSEAGb9ECWmEzf6FQbrB
   Z9w7lshQhqowtrbLDFw4rXAxZuE=
   -----END PRIVATE KEY-----




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   The same item dumped as asn1 yields:

     0 114: SEQUENCE {
     2   1:   INTEGER 1
     5   5:   SEQUENCE {
     7   3:     OBJECT IDENTIFIER '1 3 101 112'
          :     }
    12  34:   OCTET STRING, encapsulates {
    14  32:     OCTET STRING D4 EE 72 DB F9 13 58 4A D5 B6 D8 F1 F7
                    69 F8 AD 3A FE 7C 28 CB F1 D4 FB E0 97 A8 8F 44
                    75 58 42
          :     }
    48  31:   [0] {
    50  29:     SEQUENCE {
    52  10:       OBJECT IDENTIFIER '1 2 840 113549 1 9 9 20'
    64  15:       SET {
    66  13:         UTF8String 'Curdle Chairs'
          :         }
          :       }
          :     }
   81  33:   [1] 00 19 BF 44 09 69 84 CD FE 85 41 BA C1 67 DC 3B
                 96 C8 50 86 AA 30 B6 B6 CB 0C 5C 38 AD 70 31 66
                 E1
          :   }

11.  Acknowledgements

   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, Brian Smith, and Alex Wilson.

   A big thank you to Symantec for kindly donating the OIDs used in this
   draft.

12.  IANA Considerations

   IANA is requested to assign a module OID from the "SMI for PKIX
   Module Identifier" registry for the ASN.1 module in Section 9.

13.  Security Considerations

   The security considerations of [RFC5280], [RFC7748], and [RFC8032]
   apply accordingly.




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   The procedures for going from a private key to a public key are
   different for when used with Diffie-Hellman and when used with
   Edwards Signatures.  This means that the same public key cannot be
   used for both ECDH and EdDSA.

14.  References

14.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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,
              <https://www.rfc-editor.org/info/rfc5280>.

   [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,
              <https://www.rfc-editor.org/info/rfc5480>.

   [RFC5958]  Turner, S., "Asymmetric Key Packages", RFC 5958,
              DOI 10.17487/RFC5958, August 2010,
              <https://www.rfc-editor.org/info/rfc5958>.

   [RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
              for Security", RFC 7748, DOI 10.17487/RFC7748, January
              2016, <https://www.rfc-editor.org/info/rfc7748>.

   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032,
              DOI 10.17487/RFC8032, January 2017,
              <https://www.rfc-editor.org/info/rfc8032>.

14.2.  Informative References

   [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, <https://www.rfc-editor.org/info/rfc3279>.






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   [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,
              <https://www.rfc-editor.org/info/rfc4055>.

   [RFC5639]  Lochter, M. and J. Merkle, "Elliptic Curve Cryptography
              (ECC) Brainpool Standard Curves and Curve Generation",
              RFC 5639, DOI 10.17487/RFC5639, March 2010,
              <https://www.rfc-editor.org/info/rfc5639>.

   [RFC7468]  Josefsson, S. and S. Leonard, "Textual Encodings of PKIX,
              PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468,
              April 2015, <https://www.rfc-editor.org/info/rfc7468>.

Appendix A.  Invalid Encodings

   There are a number of things that need to be dealt with when a new
   key part is decoded and imported into the system.  A partial list of
   these includes:

   o  ASN.1 encoding errors: Two items are highlighted here.  First, the
      use of an OCTET STRING rather than a BIT STRING for the public
      key.  This was an incorrect copy of the structure from [RFC5958]
      which was corrected before publication.  However, any early
      implementation may have this wrong.  Second, the value of the
      version field is required to be 0 if the publicKey is absent and 1
      if present.  This is called out in [RFC5958] but is not duplicated
      in the main text.

   o  Key encoding errors: Both [RFC7748] and [RFC8032] have formatting
      requirements for keys that need to be enforced.  In some cases the
      enforcement is done at the time of importing, for example doing
      masking or a mod p operation.  In other cases the enforcement is
      done by rejecting the keys and having an import failure.

   o  Key mismatch errors: If a public key is provided, it may not agree
      with the private key either because it is wrong or the wrong
      algorithm was used.

   Some systems are also going to be stricter on what they accept.  As
   stated in [RFC5958], BER decoding of OneAsymmetricKey objects is a
   requirement for compliance.  Despite this requirement, some acceptors
   will only decode DER formats.  The following is a BER encoding of a
   private key, as such is is valid, but it may not be accepted by many
   systems.




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   -----BEGIN PRIVATE KEY-----
   MIACAQAwgAYDK2VwAAAEIgQg1O5y2/kTWErVttjx92n4rTr+fCjL8dT74Jeoj0R1W
   EIAAA==
   -----END PRIVATE KEY-----

   What follows here is a brief sampling of some incorrect keys.

   In the following example, the private key does not match the masking
   requirements for X25519.  For this example the top bits are set to
   zero and the bottom three bits are set to 001.

   -----BEGIN PRIVATE KEY-----
   MFMCAQEwBQYDK2VuBCIEIPj///////////////////////////////////////8/oS
   MDIQCEfA0sN1I082XmYJVRh6NzWg92E9FgnTpqTYxTrqpaIg==
   -----END PRIVATE KEY-----

   In the following examples, the key is the wrong length because an all
   zero byte has been removed.  In one case the first byte has been
   removed, in the other case the last byte has been removed.

   -----BEGIN PRIVATE KEY-----
   MFICAQEwBQYDK2VwBCIEIC3GfeUYbZGTAhwLEE2cbvJL7ivTlcy17VottfN6L8HwoS
   IDIADBfk2Lv/J8H7YYwj/OmIcDx++jzVkKrKwS0/HjyQyM
   -----END PRIVATE KEY-----

   -----BEGIN PRIVATE KEY-----
   MFICAQEwBQYDK2VwBCIEILJXn1VaLqvausjUaZexwI/ozmOFjfEk78KcYN+7hsNJoS
   IDIACdQhJwzi/MCGcsQeQnIUh2JFybDxSrZxuLudJmpJLk
   -----END PRIVATE KEY-----

Authors' Addresses

   Simon Josefsson
   SJD AB

   Email: simon@josefsson.org


   Jim Schaad
   August Cellars

   Email: ietf@augustcellars.com









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