RFC 7670

Generic Raw Public-Key Support for IKEv2

📅 published January 2016, from ietf

RFC 7670: Generic Raw Public-Key Support for IKEv2 🎀

okay so this is RFC 7670 💖 published in January 2016, and it's a Standards Track document 👑 (real official spec energy). T. Kivinen (INSIDE Secure), P. Wouters (Red Hat), and H. Tschofenig wrote it, and it's filed as ISSN 2070-1721 ✨. The big headline is that it updates RFC 7296, which is the IKEv2 spec itself 🧚. There's no Obsoletes line, so nothing gets replaced 🌸.

Abstract ✨

okay so IKEv2 did have raw public keys already, but it only supported RSA 🙈. In constrained environments (think tiny smart devices 🍓), other kinds of keys like the Elliptic Curve Cryptography ones are super useful. This doc updates RFC 7296 and adds support for other types of raw public keys to IKEv2 💅.

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 5741.

Info about the current status of this document, any errata, and how to give feedback is at http://www.rfc-editor.org/info/rfc7670.

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  . . . . . . . . . . . . . . . . . . . . . . . .   2
2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
3.  Certificate Encoding Payload  . . . . . . . . . . . . . . . .   3
4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
  6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
  6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .   7
  A.1.  ECDSA Example . . . . . . . . . . . . . . . . . . . . . .   7
  A.2.  RSA Example . . . . . . . . . . . . . . . . . . . . . . .   8
Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  10
Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1. Introduction 🎀

okay so this doc swaps out the algorithm-specific version of raw public keys in IKEv2 [RFC7296] for a generic version that doesn't care which algorithm you use 💖.

In [RFC5996], IKEv2 supported PKCS #1 encoded RSA keys, meaning a DER-encoded RSAPublicKey structure (see [RSA] and [RFC3447]). Other raw public-key types were not supported, though 🙈. [RFC7296] removed that feature, and this document brings raw public-key support back to IKEv2 in a more generic way ✨.

DNSSEC lets public keys be tied to domain names so they can be used with security protocols like IKEv2 and Transport Layer Security (TLS) [RFC5246], but it depends on extensions to those protocols being specified first 🧚.

The Raw Public Keys in Transport Layer Security specification ([RFC7250]) adds generic raw public-key support to TLS by reusing the SubjectPublicKeyInfo format from the X.509 Public-Key Infrastructure Certificate profile [RFC5280] 🌸.

This document is basically the same idea as that TLS spec, just applied to IKEv2 so it can support all the public-key formats defined by PKIX 👑. Bonus: future public-key extensions will work without IKEv2 needing more upgrades 💅.

To support new public-key types in IKEv2, we need these changes:

  • A new Certificate Encoding format has to be defined for carrying the SubjectPublicKeyInfo structure. Section 3 specifies this new encoding format.
  • A new Certificate Encoding has to be allocated by IANA. Section 5 has the details about the IANA registration.

The base IKEv2 spec includes support for RSA and DSA signatures, but the Signature Authentication in IKEv2 [RFC7427] extended IKEv2 so signature methods over any key type can be used 🔥. Implementations using raw public keys SHOULD use the Digital Signature method described in RFC 7427.

With raw public keys, the authenticated identity usually isn't the identity from the ID payload. Instead, the public key itself is used as the identity for the other end 🙈. That means the ID payload contents might not be useful for authentication. They could still help with policy decisions, like making the policy lookup simpler. Or you can use the ID_NULL type [RFC7619] to say the ID payload isn't relevant to this authentication 💜.

2. 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. Certificate Encoding Payload 🦋

Section 3.6 of RFC 7296 defines the Certificate payload format, shown in Figure 1 below 💖.

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Cert Encoding |                                               |
   +-+-+-+-+-+-+-+-+                                               |
   ~                       Certificate Data                        ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: Certificate Payload Format

To support raw public keys, the fields work like this:

  • Certificate Encoding (1 octet): this tells you what kind of certificate, or certificate-related info, is in the Certificate Data field 🎀.
   Certificate Encoding                 Value
   ----------------------------------------------------
   Raw Public Key                       15
  • Certificate Data (variable length): the actual encoding of the certificate data 🌸.

okay so to say the key type when the encoding is "Raw Public Key", the SubjectPublicKeyInfo structure from the PKIX certificate gets used 🧚. It's a super simple encoding, since most of the ASN.1 part can be included literally and recognized by block comparison. See Appendix A of [RFC7250] for a detailed breakdown. This document's Appendix A also has a few examples 💅.

Besides the Certificate payload, the Cert Encoding for Raw Public Key can also go in the Certificate Request payload. In that case, the Certification Authority field MUST be empty if the "Raw Public Key" certificate encoding is used 🙈.

For RSA keys, implementations MUST follow the public-key processing rules of Section 1.2 of the Additional Algorithms and Identifiers for RSA Cryptography for PKIX ([RFC4055]). This still applies even when the SubjectPublicKeyInfo isn't part of a certificate and is sent as a Certificate Data field instead 👑. What that means is that RSASSA-PSS and RSASSA-PSS-params inside the SubjectPublicKeyInfo structure MUST be sent when applicable 🔥.

4. Security Considerations 🔥

⚠️ bestie, this part is serious, so read it closely 💀

An IKEv2 deployment using raw public keys needs an out-of-band public-key validation procedure to be confident the keys are authentic 🙈. One way to get there is a configuration mechanism that provisions raw public keys into the IKEv2 software. "Smart object" deployments are likely to use such preconfigured public keys 🍓.

Another approach is to rely on secure DNS to associate public keys with domain names, using the IPSECKEY DNS RRtype [RFC4025] 🌈. More info is in DNS-Based Authentication of Named Entities (DANE) [RFC6394] 💜.

This document does not change the security assumptions made by the IKEv2 specification, since "Raw RSA Key" support was already available in IKEv2 in [RFC5996] ✨. This document only generalizes raw public-key support 🦋.

5. IANA Considerations 🧚

This document allocates a new value from the IKEv2 Certificate Encodings registry:

15      Raw Public Key

6. References 💖

6.1. 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>.

[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>.

[RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
           Kivinen, "Internet Key Exchange Protocol Version 2
           (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
           2014, <http://www.rfc-editor.org/info/rfc7296>.

[RFC7427]  Kivinen, T. and J. Snyder, "Signature Authentication in
           the Internet Key Exchange Version 2 (IKEv2)", RFC 7427,
           DOI 10.17487/RFC7427, January 2015,
           <http://www.rfc-editor.org/info/rfc7427>.

[RFC7619]  Smyslov, V. and P. Wouters, "The NULL Authentication
           Method in the Internet Key Exchange Protocol Version 2
           (IKEv2)", RFC 7619, DOI 10.17487/RFC7619, August 2015,
           <http://www.rfc-editor.org/info/rfc7619>.

🧚 to be continued! Part 2 picks up with 6.2 Informative References, then Appendix A (the ECDSA and RSA examples), Acknowledgements and Authors' Addresses, so don't go anywhere bestie 💜🫶

6.2. Informative References 📚✨

Okay, the informative references are the extra reading list, the stuff that helps you understand the vibes but isn't strictly required to implement this. Here they all are, full details included 🫶

Appendix A. Examples 🎀

Okay, this appendix is the good stuff. It shows real examples of the actual payloads that get sent on the wire 🔥

A.1. ECDSA Example 💜

This first example uses the 256-bit ECDSA private/public key pair defined in Section 8.1 of the IKEv2 ECDSA document [RFC4754].

The public key is as follows:

  • Algorithm: id-ecPublicKey (1.2.840.10045.2.1)
  • Fixed curve: secp256r1 (1.2.840.10045.3.1.7)
  • Public key x coordinate:
cb28e099 9b9c7715 fd0a80d8 e47a7707
9716cbbf 917dd72e 97566ea1 c066957c
  • Public key y coordinate:
2b57c023 5fb74897 68d058ff 4911c20f
dbe71e36 99d91339 afbb903e e17255dc

The SubjectPublicKeyInfo ASN.1 object is as follows:

0000 :     SEQUENCE
0002 :       SEQUENCE
0004 :         OBJECT IDENTIFIER  id-ecPublicKey (1.2.840.10045.2.1)
000d :         OBJECT IDENTIFIER  secp256r1 (1.2.840.10045.3.1.7)
0017 :       BIT STRING  (66 bytes)
00000000: 0004 cb28 e099 9b9c 7715 fd0a 80d8 e47a
00000010: 7707 9716 cbbf 917d d72e 9756 6ea1 c066
00000020: 957c 2b57 c023 5fb7 4897 68d0 58ff 4911
00000030: c20f dbe7 1e36 99d9 1339 afbb 903e e172
00000040: 55dc

The first byte (00) of the bit string indicates that there is no "number of unused bits", and the second byte (04) indicates uncompressed form ([RFC5480]). Those two octets are followed by the values of X and Y.

The final encoded SubjectPublicKeyInfo object is as follows:

00000000: 3059 3013 0607 2a86 48ce 3d02 0106 082a
00000010: 8648 ce3d 0301 0703 4200 04cb 28e0 999b
00000020: 9c77 15fd 0a80 d8e4 7a77 0797 16cb bf91
00000030: 7dd7 2e97 566e a1c0 6695 7c2b 57c0 235f
00000040: b748 9768 d058 ff49 11c2 0fdb e71e 3699
00000050: d913 39af bb90 3ee1 7255 dc

This will result in the final IKEv2 Certificate Payload:

00000000: NN00 0060 0f30 5930 1306 072a 8648 ce3d
00000010: 0201 0608 2a86 48ce 3d03 0107 0342 0004
00000020: cb28 e099 9b9c 7715 fd0a 80d8 e47a 7707
00000030: 9716 cbbf 917d d72e 9756 6ea1 c066 957c
00000040: 2b57 c023 5fb7 4897 68d0 58ff 4911 c20f
00000050: dbe7 1e36 99d9 1339 afbb 903e e172 55dc

Where NN is the next payload type (i.e., the type of payload that immediately follows this Certificate payload).

A.2. RSA Example 🌸

This second example uses a random 1024-bit RSA key.

The public key is as follows:

  • Algorithm: rsaEncryption (1.2.840.113549.1.1.1)
  • Modulus n (1024 bits, decimal):
1323562071162740912417075551025599045700
3972512968992059076067098474693867078469
7654066339302927451756327389839253751712
9485277759962777278073526290329821841100
9721044682579432931952695408402169276996
5181887843758615443536914372816830537901
8976615344413864477626646564638249672329
04996914356093900776754835411
  • Modulus n (1024 bits, hexadecimal):
bc7b4347 49c7b386 00bfa84b 44f88187 9a2dda08 d1f0145a
f5806c2a ed6a6172 ff0dc3d4 cd601638 e8ca348e bdca5742
31cadc97 12e209b1 fddba58a 8c62b369 038a3d1e aa727c1f
39ae49ed 6ebc30f8 d9b52e23 385a4019 15858c59 be72f343
fb1eb87b 16ffc5ab 0f8f8fe9 f7cb3e66 3d8fe9f9 ecfa1230
66f36835 8ceaefd3
  • Exponent e (17 bits, decimal): 65537
  • Exponent e (17 bits, hexadecimal): 10001

The SubjectPublicKeyInfo ASN.1 object is as follows:

0000 :     SEQUENCE
0003 :       SEQUENCE
0005 :         OBJECT IDENTIFIER rsaEncryption (1.2.840.113549.1.1.1)
0016 :         NULL
0018 :       BIT STRING  (141 bytes)
00000000: 0030 8189 0281 8100 bc7b 4347 49c7 b386
00000010: 00bf a84b 44f8 8187 9a2d da08 d1f0 145a
00000020: f580 6c2a ed6a 6172 ff0d c3d4 cd60 1638
00000030: e8ca 348e bdca 5742 31ca dc97 12e2 09b1
00000040: fddb a58a 8c62 b369 038a 3d1e aa72 7c1f
00000050: 39ae 49ed 6ebc 30f8 d9b5 2e23 385a 4019
00000060: 1585 8c59 be72 f343 fb1e b87b 16ff c5ab
00000070: 0f8f 8fe9 f7cb 3e66 3d8f e9f9 ecfa 1230
00000080: 66f3 6835 8cea efd3 0203 0100 01

The first byte (00) of the bit string indicates that there is no "number of unused bits". Inside that bit string, there is an ASN.1 sequence having 2 integers. The second byte (30) indicates that this is the beginning of the sequence, and the next byte (81) indicates the length does not fit in 7 bits, but requires one byte, so the length is in the next byte (89). Then starts the first integer with tag (02) and length (81 81). After that we have the modulus (prefixed with 0 so it will not be a negative number). After the modulus, there follows the tag (02) and length (03) of the exponent, and the last 3 bytes are the exponent.

The final encoded SubjectPublicKeyInfo object is as follows:

00000000: 3081 9f30 0d06 092a 8648 86f7 0d01 0101
00000010: 0500 0381 8d00 3081 8902 8181 00bc 7b43
00000020: 4749 c7b3 8600 bfa8 4b44 f881 879a 2dda
00000030: 08d1 f014 5af5 806c 2aed 6a61 72ff 0dc3
00000040: d4cd 6016 38e8 ca34 8ebd ca57 4231 cadc
00000050: 9712 e209 b1fd dba5 8a8c 62b3 6903 8a3d
00000060: 1eaa 727c 1f39 ae49 ed6e bc30 f8d9 b52e
00000070: 2338 5a40 1915 858c 59be 72f3 43fb 1eb8
00000080: 7b16 ffc5 ab0f 8f8f e9f7 cb3e 663d 8fe9
00000090: f9ec fa12 3066 f368 358c eaef d302 0301
000000a0: 0001

This will result in the final IKEv2 Certificate Payload:

00000000: NN00 00a7 0f30 819f 300d 0609 2a86 4886
00000010: f70d 0101 0105 0003 818d 0030 8189 0281
00000020: 8100 bc7b 4347 49c7 b386 00bf a84b 44f8
00000030: 8187 9a2d da08 d1f0 145a f580 6c2a ed6a
00000040: 6172 ff0d c3d4 cd60 1638 e8ca 348e bdca
00000050: 5742 31ca dc97 12e2 09b1 fddb a58a 8c62
00000060: b369 038a 3d1e aa72 7c1f 39ae 49ed 6ebc
00000070: 30f8 d9b5 2e23 385a 4019 1585 8c59 be72
00000080: f343 fb1e b87b 16ff c5ab 0f8f 8fe9 f7cb
00000090: 3e66 3d8f e9f9 ecfa 1230 66f3 6835 8cea
000000a0: efd3 0203 0100 01

Where NN is the next payload type (i.e., the type of the payload that immediately follows this Certificate payload).

Acknowledgements 🫶

This document reproduces some parts of the similar TLS document ([RFC7250]).

Authors' Addresses 💌

Tero Kivinen
INSIDE Secure
Eerikinkatu 28
Helsinki  FI-00180
Finland

Email: kivinen@iki.fi


Paul Wouters
Red Hat

Email: pwouters@redhat.com


Hannes Tschofenig

Email: Hannes.Tschofenig@gmx.net
URI:   http://www.tschofenig.priv.at
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