rfc8418
Internet Engineering Task Force (IETF) R. Housley
Request for Comments: 8418 Vigil Security
Category: Standards Track August 2018
ISSN: 2070-1721
Use of the Elliptic Curve Diffie-Hellman Key Agreement Algorithm
with X25519 and X448 in the Cryptographic Message Syntax (CMS)
Abstract
This document describes the conventions for using the Elliptic Curve
Diffie-Hellman (ECDH) key agreement algorithm with curve25519 and
curve448 in the Cryptographic Message Syntax (CMS).
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
https://www.rfc-editor.org/info/rfc8418.
Copyright Notice
Copyright (c) 2018 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
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.
Housley Standards Track [Page 1]
RFC 8418 Using X25519 and X448 with CMS August 2018
Table of Contents
1. Introduction ....................................................2
1.1. Terminology ................................................3
1.2. ASN.1 ......................................................3
2. Key Agreement ...................................................3
2.1. ANSI-X9.63-KDF .............................................4
2.2. HKDF .......................................................5
3. Enveloped-data Conventions ......................................5
3.1. EnvelopedData Fields .......................................6
3.2. KeyAgreeRecipientInfo Fields ...............................6
4. Authenticated-data Conventions ..................................7
4.1. AuthenticatedData Fields ...................................8
4.2. KeyAgreeRecipientInfo Fields ...............................8
5. Authenticated-enveloped-data Conventions ........................8
5.1. AuthEnvelopedData Fields ...................................8
5.2. KeyAgreeRecipientInfo Fields ...............................8
6. Certificate Conventions .........................................9
7. Key Agreement Algorithm Identifiers .............................9
8. SMIMECapabilities Attribute Conventions ........................10
9. Security Considerations ........................................11
10. IANA Considerations ...........................................12
11. References ....................................................13
11.1. Normative References .....................................13
11.2. Informative References ...................................14
Appendix A. ASN.1 Module ..........................................16
Acknowledgements ..................................................18
Author's Address ..................................................18
1. Introduction
This document describes the conventions for using Elliptic Curve
Diffie-Hellman (ECDH) key agreement using curve25519 and curve448
[CURVES] in the Cryptographic Message Syntax (CMS) [CMS]. Key
agreement is supported in three CMS content types: the enveloped-data
content type [CMS], authenticated-data content type [CMS], and the
authenticated-enveloped-data content type [AUTHENV].
The conventions for using some Elliptic Curve Cryptography (ECC)
algorithms in CMS are described in [CMSECC]. These conventions cover
the use of ECDH with some curves other than curve25519 and curve448
[CURVES]. Those other curves are not deprecated.
Using curve25519 with Diffie-Hellman key agreement is referred to as
"X25519". Using curve448 with Diffie-Hellman key agreement is
referred to as "X448".
Housley Standards Track [Page 2]
RFC 8418 Using X25519 and X448 with CMS August 2018
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. ASN.1
CMS values are generated using ASN.1 [X680], which uses the Basic
Encoding Rules (BER) and the Distinguished Encoding Rules (DER)
[X690].
2. Key Agreement
In 1976, Diffie and Hellman described a means for two parties to
agree upon a shared secret value in a manner that prevents
eavesdroppers from learning the shared secret value [DH1976]. This
secret may then be converted into pairwise symmetric keying material
for use with other cryptographic algorithms. Over the years, many
variants of this fundamental technique have been developed. This
document describes the conventions for using Ephemeral-Static
Elliptic Curve Diffie-Hellman (ECDH) key agreement using X25519 and
X448 [CURVES].
The originator MUST use an ephemeral public/private key pair that is
generated on the same elliptic curve as the public key of the
recipient. The ephemeral key pair MUST be used for a single CMS-
protected content type, and then it MUST be discarded. The
originator obtains the recipient's static public key from the
recipient's certificate [PROFILE].
X25519 is described in Section 6.1 of [CURVES], and X448 is described
in Section 6.2 of [CURVES]. Conforming implementations MUST check
whether the computed Diffie-Hellman shared secret is the all-zero
value, and abort if so, as described in Section 6 of [CURVES]. If an
alternative implementation of these elliptic curves to that
documented in Section 6 of [CURVES] is employed, then the additional
checks specified in Section 7 of [CURVES] SHOULD be performed.
In [CURVES], the shared secret value that is produced by ECDH is
called K. (In some other specifications, the shared secret value is
called Z.) A Key Derivation Function (KDF) is used to produce a
pairwise key-encryption key (KEK) from the shared secret value (K),
the length of the KEK, and the DER-encoded ECC-CMS-SharedInfo
structure [CMSECC].
Housley Standards Track [Page 3]
RFC 8418 Using X25519 and X448 with CMS August 2018
The ECC-CMS-SharedInfo definition from [CMSECC] is repeated here for
convenience.
ECC-CMS-SharedInfo ::= SEQUENCE {
keyInfo AlgorithmIdentifier,
entityUInfo [0] EXPLICIT OCTET STRING OPTIONAL,
suppPubInfo [2] EXPLICIT OCTET STRING }
The ECC-CMS-SharedInfo keyInfo field contains the object identifier
of the key-encryption algorithm and associated parameters. This
algorithm will be used to wrap the content-encryption key. For
example, the AES Key Wrap algorithm [AESKW] does not need parameters,
so the algorithm identifier parameters are absent.
The ECC-CMS-SharedInfo entityUInfo field optionally contains
additional keying material supplied by the sending agent. Note that
[CMS] requires implementations to accept a KeyAgreeRecipientInfo
SEQUENCE that includes the ukm field. If the ukm field is present,
the ukm is placed in the entityUInfo field. By including the ukm, a
different KEK is generated even when the originator ephemeral private
key is improperly used more than once. Therefore, if the ukm field
is present, it MUST be selected in a manner that provides, with very
high probability, a unique value; however, there is no security
benefit to using a ukm value that is longer than the KEK that will be
produced by the KDF.
The ECC-CMS-SharedInfo suppPubInfo field contains the length of the
generated KEK, in bits, represented as a 32-bit number in network
byte order. For example, the key length for AES-256 [AES] would be
0x00000100.
2.1. ANSI-X9.63-KDF
The ANSI-X9.63-KDF key derivation function is a simple construct
based on a one-way hash function described in American National
Standard X9.63 [X963]. This KDF is also described in Section 3.6.1
of [SEC1].
Three values are concatenated to produce the input string to the KDF:
1. The shared secret value generated by ECDH, K.
2. The iteration counter, starting with one, as described below.
3. The DER-encoded ECC-CMS-SharedInfo structure.
To generate a key-encryption key (KEK), the KDF generates one or more
keying material (KM) blocks, with the counter starting at 0x00000001,
and incrementing the counter for each subsequent KM block until
enough material has been generated. The 32-bit counter is
Housley Standards Track [Page 4]
RFC 8418 Using X25519 and X448 with CMS August 2018
represented in network byte order. The KM blocks are concatenated
left to right, and then the leftmost portion of the result is used as
the pairwise key-encryption key, KEK:
KM(i) = Hash(K || INT32(counter=i) || DER(ECC-CMS-SharedInfo))
KEK = KM(counter=1) || KM(counter=2) ...
2.2. HKDF
The Extract-and-Expand HMAC-based Key Derivation Function (HKDF) is a
robust construct based on a one-way hash function described in RFC
5869 [HKDF]. HKDF is comprised of two steps: HKDF-Extract followed
by HKDF-Expand.
Three values are used as inputs to the HKDF:
1. The shared secret value generated by ECDH, K.
2. The length in octets of the keying data to be generated.
3. The DER-encoded ECC-CMS-SharedInfo structure.
The ECC-CMS-SharedInfo structure optionally includes the ukm. If the
ukm is present, the ukm is also used as the HKDF salt. HKDF uses an
appropriate number of zero octets when no salt is provided.
The length of the generated KEK is used in two places, once in bits
and once in octets. The ECC-CMS-SharedInfo structure includes the
length of the generated KEK in bits. The HKDF-Expand function takes
an argument for the length of the generated KEK in octets.
In summary, to produce the pairwise key-encryption key, KEK:
if ukm is provided, then salt = ukm, else salt is not provided
PRK = HKDF-Extract(salt, K)
KEK = HKDF-Expand(PRK, DER(ECC-CMS-SharedInfo), SizeInOctets(KEK))
3. Enveloped-data Conventions
The CMS enveloped-data content type [CMS] consists of an encrypted
content and wrapped content-encryption keys for one or more
recipients. The ECDH key agreement algorithm is used to generate a
pairwise KEK between the originator and a particular recipient.
Then, the KEK is used to wrap the content-encryption key for that
recipient. When there is more than one recipient, the same content-
encryption key MUST be wrapped for each of them.
Housley Standards Track [Page 5]
RFC 8418 Using X25519 and X448 with CMS August 2018
A compliant implementation MUST meet the requirements for
constructing an enveloped-data content type in Section 6 of [CMS].
A content-encryption key MUST be randomly generated for each instance
of an enveloped-data content type. The content-encryption key is
used to encrypt the content.
3.1. EnvelopedData Fields
The enveloped-data content type is ASN.1 encoded using the
EnvelopedData syntax. The fields of the EnvelopedData syntax MUST be
populated as described in Section 6 of [CMS]. The RecipientInfo
choice is described in Section 6.2 of [CMS], and repeated here for
convenience.
RecipientInfo ::= CHOICE {
ktri KeyTransRecipientInfo,
kari [1] KeyAgreeRecipientInfo,
kekri [2] KEKRecipientInfo,
pwri [3] PasswordRecipientinfo,
ori [4] OtherRecipientInfo }
For the recipients that use X25519 or X448, the RecipientInfo kari
choice MUST be used.
3.2. KeyAgreeRecipientInfo Fields
The fields of the KeyAgreeRecipientInfo syntax MUST be populated as
described in this section when X25519 or X448 is employed for one or
more recipients.
The KeyAgreeRecipientInfo version MUST be 3.
The KeyAgreeRecipientInfo originator provides three alternatives for
identifying the originator's public key, and the originatorKey
alternative MUST be used. The originatorKey MUST contain an
ephemeral key for the originator. The originatorKey algorithm field
MUST contain the id-X25519 or the id-X448 object identifier. The
originator's ephemeral public key MUST be encoded as an OCTET STRING.
The object identifiers for X25519 and X448 have been assigned in
[RFC8410]. They are repeated below for convenience.
Housley Standards Track [Page 6]
RFC 8418 Using X25519 and X448 with CMS August 2018
When using X25519, the public key contains exactly 32 octets, and the
id-X25519 object identifier is used:
id-X25519 OBJECT IDENTIFIER ::= { 1 3 101 110 }
When using X448, the public key contains exactly 56 octets, and the
id-X448 object identifier is used:
id-X448 OBJECT IDENTIFIER ::= { 1 3 101 111 }
KeyAgreeRecipientInfo ukm is optional. The processing of the ukm
with the ANSI-X9.63-KDF key derivation function is described in
Section 2.1, and the processing of the ukm with the HKDF key
derivation function is described in Section 2.2.
The KeyAgreeRecipientInfo keyEncryptionAlgorithm MUST contain the
object identifier of the key-encryption algorithm that will be used
to wrap the content-encryption key. The conventions for using
AES-128, AES-192, and AES-256 in the key wrap mode are specified in
[CMSAES].
The KeyAgreeRecipientInfo recipientEncryptedKeys includes a recipient
identifier and encrypted key for one or more recipients. The
RecipientEncryptedKey KeyAgreeRecipientIdentifier MUST contain either
the issuerAndSerialNumber identifying the recipient's certificate or
the RecipientKeyIdentifier containing the subject key identifier from
the recipient's certificate. In both cases, the recipient's
certificate contains the recipient's static X25519 or X448 public
key. The RecipientEncryptedKey EncryptedKey MUST contain the
content-encryption key encrypted with the pairwise key-encryption key
using the algorithm specified by the KeyWrapAlgorithm.
4. Authenticated-data Conventions
The CMS authenticated-data content type [CMS] consists of an
authenticated content, a message authentication code (MAC), and
encrypted authentication keys for one or more recipients. The ECDH
key agreement algorithm is used to generate a pairwise KEK between
the originator and a particular recipient. Then, the KEK is used to
wrap the authentication key for that recipient. When there is more
than one recipient, the same authentication key MUST be wrapped for
each of them.
A compliant implementation MUST meet the requirements for
constructing an authenticated-data content type in Section 9 of
[CMS].
Housley Standards Track [Page 7]
RFC 8418 Using X25519 and X448 with CMS August 2018
An authentication key MUST be randomly generated for each instance of
an authenticated-data content type. The authentication key is used
to compute the MAC over the content.
4.1. AuthenticatedData Fields
The authenticated-data content type is ASN.1 encoded using the
AuthenticatedData syntax. The fields of the AuthenticatedData syntax
MUST be populated as described in [CMS]; for the recipients that use
X25519 or X448, the RecipientInfo kari choice MUST be used.
4.2. KeyAgreeRecipientInfo Fields
The fields of the KeyAgreeRecipientInfo syntax MUST be populated as
described in Section 3.2 of this document.
5. Authenticated-enveloped-data Conventions
The CMS authenticated-enveloped-data content type [AUTHENV] consists
of an authenticated and encrypted content and encrypted content-
authenticated-encryption keys for one or more recipients. The ECDH
key agreement algorithm is used to generate a pairwise KEK between
the originator and a particular recipient. Then, the KEK is used to
wrap the content-authenticated-encryption key for that recipient.
When there is more than one recipient, the same content-
authenticated-encryption key MUST be wrapped for each of them.
A compliant implementation MUST meet the requirements for
constructing an authenticated-data content type in Section 2 of
[AUTHENV].
A content-authenticated-encryption key MUST be randomly generated for
each instance of an authenticated-enveloped-data content type. The
content-authenticated-encryption key is used to authenticate and
encrypt the content.
5.1. AuthEnvelopedData Fields
The authenticated-enveloped-data content type is ASN.1 encoded using
the AuthEnvelopedData syntax. The fields of the AuthEnvelopedData
syntax MUST be populated as described in [AUTHENV]; for the
recipients that use X25519 or X448, the RecipientInfo kari choice
MUST be used.
5.2. KeyAgreeRecipientInfo Fields
The fields of the KeyAgreeRecipientInfo syntax MUST be populated as
described in Section 3.2 of this document.
Housley Standards Track [Page 8]
RFC 8418 Using X25519 and X448 with CMS August 2018
6. Certificate Conventions
RFC 5280 [PROFILE] specifies the profile for using X.509 Certificates
in Internet applications. A recipient static public key is needed
for X25519 or X448, and the originator obtains that public key from
the recipient's certificate. The conventions for carrying X25519 and
X448 public keys are specified in [RFC8410].
7. Key Agreement Algorithm Identifiers
The following object identifiers are assigned in [CMSECC] to indicate
ECDH with ANSI-X9.63-KDF using various one-way hash functions. These
are expected to be used as AlgorithmIdentifiers with a parameter that
specifies the key-encryption algorithm. These are repeated here for
convenience.
secg-scheme OBJECT IDENTIFIER ::= {
iso(1) identified-organization(3) certicom(132) schemes(1) }
dhSinglePass-stdDH-sha256kdf-scheme OBJECT IDENTIFIER ::= {
secg-scheme 11 1 }
dhSinglePass-stdDH-sha384kdf-scheme OBJECT IDENTIFIER ::= {
secg-scheme 11 2 }
dhSinglePass-stdDH-sha512kdf-scheme OBJECT IDENTIFIER ::= {
secg-scheme 11 3 }
The following object identifiers are assigned to indicate ECDH with
HKDF using various one-way hash functions. These are expected to be
used as AlgorithmIdentifiers with a parameter that specifies the
key-encryption algorithm.
smime-alg OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-9(9) smime(16) alg(3) }
dhSinglePass-stdDH-hkdf-sha256-scheme OBJECT IDENTIFIER ::= {
smime-alg 19 }
dhSinglePass-stdDH-hkdf-sha384-scheme OBJECT IDENTIFIER ::= {
smime-alg 20 }
dhSinglePass-stdDH-hkdf-sha512-scheme OBJECT IDENTIFIER ::= {
smime-alg 21 }
Housley Standards Track [Page 9]
RFC 8418 Using X25519 and X448 with CMS August 2018
8. SMIMECapabilities Attribute Conventions
A sending agent MAY announce to other agents that it supports ECDH
key agreement using the SMIMECapabilities signed attribute in a
signed message [SMIME] or a certificate [CERTCAP]. Following the
pattern established in [CMSECC], the SMIMECapabilities associated
with ECDH carries a DER-encoded object identifier that identifies
support for ECDH in conjunction with a particular KDF, and it
includes a parameter that names the key wrap algorithm.
The following SMIMECapabilities values (in hexadecimal) from [CMSECC]
might be of interest to implementations that support X25519 and X448:
ECDH with ANSI-X9.63-KDF using SHA-256; uses AES-128 key wrap:
30 15 06 06 2B 81 04 01 0B 01 30 0B 06 09 60 86 48 01 65 03 04
01 05
ECDH with ANSI-X9.63-KDF using SHA-384; uses AES-128 key wrap:
30 15 06 06 2B 81 04 01 0B 02 30 0B 06 09 60 86 48 01 65 03 04
01 05
ECDH with ANSI-X9.63-KDF using SHA-512; uses AES-128 key wrap:
30 15 06 06 2B 81 04 01 0B 03 30 0B 06 09 60 86 48 01 65 03 04
01 05
ECDH with ANSI-X9.63-KDF using SHA-256; uses AES-256 key wrap:
30 15 06 06 2B 81 04 01 0B 01 30 0B 06 09 60 86 48 01 65 03 04
01 2D
ECDH with ANSI-X9.63-KDF using SHA-384; uses AES-256 key wrap:
30 15 06 06 2B 81 04 01 0B 02 30 0B 06 09 60 86 48 01 65 03 04
01 2D
ECDH with ANSI-X9.63-KDF using SHA-512; uses AES-256 key wrap:
30 15 06 06 2B 81 04 01 0B 03 30 0B 06 09 60 86 48 01 65 03 04
01 2D
Housley Standards Track [Page 10]
RFC 8418 Using X25519 and X448 with CMS August 2018
The following SMIMECapabilities values (in hexadecimal) based on the
algorithm identifiers in Section 7 of this document might be of
interest to implementations that support X25519 and X448:
ECDH with HKDF using SHA-256; uses AES-128 key wrap:
30 1A 06 0B 2A 86 48 86 F7 0D 01 09 10 03 13 30 0B 06 09 60 86
48 01 65 03 04 01 05
ECDH with HKDF using SHA-384; uses AES-128 key wrap:
30 1A 06 0B 2A 86 48 86 F7 0D 01 09 10 03 14 30 0B 06 09 60 86
48 01 65 03 04 01 05
ECDH with HKDF using SHA-512; uses AES-128 key wrap:
30 1A 06 0B 2A 86 48 86 F7 0D 01 09 10 03 15 30 0B 06 09 60 86
48 01 65 03 04 01 05
ECDH with HKDF using SHA-256; uses AES-256 key wrap:
30 1A 06 0B 2A 86 48 86 F7 0D 01 09 10 03 13 30 0B 06 09 60 86
48 01 65 03 04 01 2D
ECDH with HKDF using SHA-384; uses AES-256 key wrap:
30 1A 06 0B 2A 86 48 86 F7 0D 01 09 10 03 14 30 0B 06 09 60 86
48 01 65 03 04 01 2D
ECDH with HKDF using SHA-512; uses AES-256 key wrap:
30 1A 06 0B 2A 86 48 86 F7 0D 01 09 10 03 15 30 0B 06 09 60 86
48 01 65 03 04 01 2D
9. Security Considerations
Please consult the security considerations of [CMS] for security
considerations related to the enveloped-data content type and the
authenticated-data content type.
Please consult the security considerations of [AUTHENV] for security
considerations related to the authenticated-enveloped-data content
type.
Please consult the security considerations of [CURVES] for security
considerations related to the use of X25519 and X448.
The originator uses an ephemeral public/private key pair that is
generated on the same elliptic curve as the public key of the
recipient. The ephemeral key pair is used for a single CMS protected
content type, and then it is discarded. If the originator wants to
be able to decrypt the content (for enveloped-data and authenticated-
enveloped-data) or check the authentication (for authenticated-data),
then the originator needs to treat themselves as a recipient.
Housley Standards Track [Page 11]
RFC 8418 Using X25519 and X448 with CMS August 2018
As specified in [CMS], implementations MUST support processing of the
KeyAgreeRecipientInfo ukm field; this ensures that interoperability
is not a concern whether the ukm is present or absent. The ukm is
placed in the entityUInfo field of the ECC-CMS-SharedInfo structure.
When present, the ukm ensures that a different key-encryption key is
generated, even when the originator ephemeral private key is
improperly used more than once.
10. IANA Considerations
One object identifier for the ASN.1 module in Appendix A was assigned
in the "SMI Security for S/MIME Module Identifiers
(1.2.840.113549.1.9.16.0)" registry on [IANA-SMI]:
id-mod-cms-ecdh-alg-2017 OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-9(9) smime(16) mod(0) 67 }
Three object identifiers for the Key Agreement Algorithm Identifiers
in Section 7 were assigned in the "SMI Security for S/MIME Algorithms
(1.2.840.113549.1.9.16.3)" registry on [IANA-SMI]:
smime-alg OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-9(9) smime(16) alg(3) }
dhSinglePass-stdDH-hkdf-sha256-scheme OBJECT IDENTIFIER ::= {
smime-alg 19 }
dhSinglePass-stdDH-hkdf-sha384-scheme OBJECT IDENTIFIER ::= {
smime-alg 20 }
dhSinglePass-stdDH-hkdf-sha512-scheme OBJECT IDENTIFIER ::= {
smime-alg 21 }
Housley Standards Track [Page 12]
RFC 8418 Using X25519 and X448 with CMS August 2018
11. References
11.1. Normative References
[AUTHENV] Housley, R., "Cryptographic Message Syntax (CMS)
Authenticated-Enveloped-Data Content Type", RFC 5083,
DOI 10.17487/RFC5083, November 2007,
<https://www.rfc-editor.org/info/rfc5083>.
[CERTCAP] Santesson, S., "X.509 Certificate Extension for
Secure/Multipurpose Internet Mail Extensions (S/MIME)
Capabilities", RFC 4262, DOI 10.17487/RFC4262, December
2005, <https://www.rfc-editor.org/info/rfc4262>.
[CMS] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
[CMSASN1] Hoffman, P. and J. Schaad, "New ASN.1 Modules for
Cryptographic Message Syntax (CMS) and S/MIME", RFC 5911,
DOI 10.17487/RFC5911, June 2010,
<https://www.rfc-editor.org/info/rfc5911>.
[CMSECC] Turner, S. and D. Brown, "Use of Elliptic Curve
Cryptography (ECC) Algorithms in Cryptographic Message
Syntax (CMS)", RFC 5753, DOI 10.17487/RFC5753, January
2010, <https://www.rfc-editor.org/info/rfc5753>.
[CURVES] 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>.
[HKDF] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>.
[PROFILE] 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>.
[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>.
Housley Standards Track [Page 13]
RFC 8418 Using X25519 and X448 with CMS August 2018
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8410] Josefsson, S., and J. Schaad, "Algorithm Identifiers for
Ed25519,Ed448, Ed448ph, X25519, and X448 for Use in the
Internet X.509 Public Key Infrastructure", RFC 8410,
DOI 10.17487/RFC8410, August 2018,
<https://www.rfc-editor.org/info/rfc8410>.
[SEC1] Standards for Efficient Cryptography, "SEC 1: Elliptic
Curve Cryptography", Cericom Research, version 2.0, May
2009, <http://www.secg.org/sec1-v2.pdf>.
[SMIME] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, DOI 10.17487/RFC5751, January
2010, <https://www.rfc-editor.org/info/rfc5751>.
[X680] ITU-T, "Information technology -- Abstract Syntax Notation
One (ASN.1): Specification of basic notation", ITU-T
Recommendation X.680, ISO/IEC 8824-1, August 2015,
<https://www.itu.int/rec/T-REC-X.680/en>.
[X690] ITU-T, "Information technology -- ASN.1 encoding rules:
Specification of Basic Encoding Rules (BER), Canonical
Encoding Rules (CER) and Distinguished Encoding Rules
(DER)", ITU-T Recommendation X.690, ISO/IEC 8825-1, August
2015, <https://www.itu.int/rec/T-REC-X.690/en>.
11.2. Informative References
[AES] National Institute of Standards and Technology, "Advanced
Encryption Standard (AES)", FIPS PUB 197, November 2001.
[AESKW] Schaad, J. and R. Housley, "Advanced Encryption Standard
(AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394,
September 2002, <https://www.rfc-editor.org/info/rfc3394>.
[CMSAES] Schaad, J., "Use of the Advanced Encryption Standard (AES)
Encryption Algorithm in Cryptographic Message Syntax
(CMS)", RFC 3565, DOI 10.17487/RFC3565, July 2003,
<https://www.rfc-editor.org/info/rfc3565>.
[DH1976] Diffie, W., and M. E. Hellman, "New Directions in
Cryptography", IEEE Trans. on Info. Theory, Vol. IT-22,
November 1976, pp. 644-654.
Housley Standards Track [Page 14]
RFC 8418 Using X25519 and X448 with CMS August 2018
[IANA-SMI] IANA, "Structure of Management Information (SMI) Numbers
(MIB Module Registrations)",
<https://www.iana.org/assignments/smi-numbers>.
[X963] American National Standards Institute, "Public-Key
Cryptography for the Financial Services Industry: Key
Agreement and Key Transport Using Elliptic Curve
Cryptography", American National Standard X9.63-2001,
November 2001.
Housley Standards Track [Page 15]
RFC 8418 Using X25519 and X448 with CMS August 2018
Appendix A. ASN.1 Module
CMSECDHAlgs-2017
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) id-mod-cms-ecdh-alg-2017(67) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL
IMPORTS
KeyWrapAlgorithm
FROM CryptographicMessageSyntaxAlgorithms-2009 -- in [CMSASN1]
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-9(9) smime(16) modules(0) id-mod-cmsalg-2001-02(37) }
KEY-AGREE, SMIME-CAPS
FROM AlgorithmInformation-2009 -- in [CMSASN1]
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-algorithmInformation-02(58) }
dhSinglePass-stdDH-sha256kdf-scheme,
dhSinglePass-stdDH-sha384kdf-scheme,
dhSinglePass-stdDH-sha512kdf-scheme,
kaa-dhSinglePass-stdDH-sha256kdf-scheme,
kaa-dhSinglePass-stdDH-sha384kdf-scheme,
kaa-dhSinglePass-stdDH-sha512kdf-scheme,
cap-kaa-dhSinglePass-stdDH-sha256kdf-scheme,
cap-kaa-dhSinglePass-stdDH-sha384kdf-scheme,
cap-kaa-dhSinglePass-stdDH-sha512kdf-scheme
FROM CMSECCAlgs-2009-02 -- in [CMSECC]
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-9(9) smime(16) modules(0)
id-mod-cms-ecc-alg-2009-02(46) }
;
Housley Standards Track [Page 16]
RFC 8418 Using X25519 and X448 with CMS August 2018
--
-- Object Identifiers
--
smime-alg OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-9(9) smime(16) alg(3) }
dhSinglePass-stdDH-hkdf-sha256-scheme OBJECT IDENTIFIER ::= {
smime-alg 19 }
dhSinglePass-stdDH-hkdf-sha384-scheme OBJECT IDENTIFIER ::= {
smime-alg 20 }
dhSinglePass-stdDH-hkdf-sha512-scheme OBJECT IDENTIFIER ::= {
smime-alg 21 }
--
-- Extend the Key Agreement Algorithms in [CMSECC]
--
KeyAgreementAlgs KEY-AGREE ::= { ...,
kaa-dhSinglePass-stdDH-sha256kdf-scheme |
kaa-dhSinglePass-stdDH-sha384kdf-scheme |
kaa-dhSinglePass-stdDH-sha512kdf-scheme |
kaa-dhSinglePass-stdDH-hkdf-sha256-scheme |
kaa-dhSinglePass-stdDH-hkdf-sha384-scheme |
kaa-dhSinglePass-stdDH-hkdf-sha512-scheme }
kaa-dhSinglePass-stdDH-hkdf-sha256-scheme KEY-AGREE ::= {
IDENTIFIER dhSinglePass-stdDH-hkdf-sha256-scheme
PARAMS TYPE KeyWrapAlgorithm ARE required
UKM -- TYPE unencoded data -- ARE preferredPresent
SMIME-CAPS cap-kaa-dhSinglePass-stdDH-hkdf-sha256-scheme }
kaa-dhSinglePass-stdDH-hkdf-sha384-scheme KEY-AGREE ::= {
IDENTIFIER dhSinglePass-stdDH-hkdf-sha384-scheme
PARAMS TYPE KeyWrapAlgorithm ARE required
UKM -- TYPE unencoded data -- ARE preferredPresent
SMIME-CAPS cap-kaa-dhSinglePass-stdDH-hkdf-sha384-scheme }
kaa-dhSinglePass-stdDH-hkdf-sha512-scheme KEY-AGREE ::= {
IDENTIFIER dhSinglePass-stdDH-hkdf-sha512-scheme
PARAMS TYPE KeyWrapAlgorithm ARE required
UKM -- TYPE unencoded data -- ARE preferredPresent
SMIME-CAPS cap-kaa-dhSinglePass-stdDH-hkdf-sha512-scheme }
Housley Standards Track [Page 17]
RFC 8418 Using X25519 and X448 with CMS August 2018
--
-- Extend the S/MIME CAPS in [CMSECC]
--
SMimeCAPS SMIME-CAPS ::= { ...,
kaa-dhSinglePass-stdDH-sha256kdf-scheme.&smimeCaps |
kaa-dhSinglePass-stdDH-sha384kdf-scheme.&smimeCaps |
kaa-dhSinglePass-stdDH-sha512kdf-scheme.&smimeCaps |
kaa-dhSinglePass-stdDH-hkdf-sha256-scheme.&smimeCaps |
kaa-dhSinglePass-stdDH-hkdf-sha384-scheme.&smimeCaps |
kaa-dhSinglePass-stdDH-hkdf-sha512-scheme.&smimeCaps }
cap-kaa-dhSinglePass-stdDH-hkdf-sha256-scheme SMIME-CAPS ::= {
TYPE KeyWrapAlgorithm
IDENTIFIED BY dhSinglePass-stdDH-hkdf-sha256-scheme }
cap-kaa-dhSinglePass-stdDH-hkdf-sha384-scheme SMIME-CAPS ::= {
TYPE KeyWrapAlgorithm
IDENTIFIED BY dhSinglePass-stdDH-hkdf-sha384-scheme}
cap-kaa-dhSinglePass-stdDH-hkdf-sha512-scheme SMIME-CAPS ::= {
TYPE KeyWrapAlgorithm
IDENTIFIED BY dhSinglePass-stdDH-hkdf-sha512-scheme }
END
Acknowledgements
Many thanks to Roni Even, Daniel Migault, Eric Rescorla, Jim Schaad,
Stefan Santesson, and Sean Turner for their review and insightful
suggestions.
Author's Address
Russ Housley
918 Spring Knoll Drive
Herndon, VA 20170
United States of America
Email: housley@vigilsec.com
Housley Standards Track [Page 18]
ERRATA
