IP Security Maintenance and Extensions T. Kivinen
(ipsecme) INSIDE Secure
Internet-Draft December 4, 2012
Updates: RFC 5996 (if approved)
Intended status: Standards Track
Expires: June 7, 2013
Signature Authentication in IKEv2
draft-kivinen-ipsecme-signature-auth-00.txt
Abstract
The Internet Key Exchange Version 2 (IKEv2) protocol has limited
support for the Elliptic Curve Digital Signature Algorithm (ECDSA).
The current support only includes support for three Elliptic Curve
groups, and there is fixed hash algorithm tied to each curve. This
document generalizes the IKEv2 signature support so it can support
any signature method supported by the PKIX and also adds signature
hash algorithm negotiation. This generic mechanism is not limited to
ECDSA, but can also be used with other signature algorithms.
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 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 June 7, 2013.
Copyright Notice
Copyright (c) 2012 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
Kivinen Expires June 7, 2013 [Page 1]
Internet-Draft Signature Authentication in IKEv2 December 2012
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Authentication Payload . . . . . . . . . . . . . . . . . . . . 4
4. Hash Algorithm Notification . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
Kivinen Expires June 7, 2013 [Page 2]
Internet-Draft Signature Authentication in IKEv2 December 2012
1. Introduction
This document adds support for new IKEv2 ([RFC5996]) authentication
method to support all kinds of signature methods. The current
signature based authentication methods in the IKEv2 are per
algorithm, i.e. there is one for RSA Digital signatures, one for DSS
Digital Signatures (using SHA-1) and three for different ECDSA curves
each tied to exactly one hash algorithm. This design starts to be
cumbersome when more ECDSA groups are added, as each of them would
require new authentication method and as with ECDSA there is no way
to extract the hash algorithm from the signature, each ECDSA
algorithm would need to come with fixed hash algorithm tied to it.
With the SHA-3 definitions coming out, it is seen that it might be
possible that in the future the signature methods are used with SHA-3
also, not only SHA-2. This means new mechanism for negotiating the
hash algorithm for the signature algorithms is needed.
The RSA Digital Signatures format in the IKEv2 is specified to use
RSASSA-PKCS1-v1_5, but there has been some discussions that newer
padding methods should also be possible (See section 5 of [RFC4055]).
The DSS Digital Signatures format in the IKEv2 is specified to always
use SHA-1, which limits the security of that, meaning there is no
point of using long keys with it.
This documents specifies two things, one is one new authentication
method, which includes the enough information inside the
Authentication payload data that the signature hash algorithm can be
extracted from there (see Section 3). The another thing is to add
indication of supported signature hash algorithms by the peer (see
Section 4). This allows peer to know which hash algorithms are
supported by the other end and use one of them (provided one is
allowed by policy). There is no need to actually negotiate one
common hash algorithm, as different hash algorithms can be used in
different directions if needed.
The new digital signature method needs to be flexible enough to
include all current signature methods (ECDSA, ECGDSA, RSASSA-PSS,
ElGamal, etc), and also allow adding new things in the future. For
this the signature algorithm is specified by and OID which specifies
both the signature and hash algorithms (i.e. sha1WithRSAEncryption,
dsa-with-sha1, dsa-with-sha256, ecdsa-with-SHA1, ecdsa-with-SHA256
etc), meaning any signature and hash algorithm specified by an OID
can be used.
Kivinen Expires June 7, 2013 [Page 3]
Internet-Draft Signature Authentication in IKEv2 December 2012
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. Authentication Payload
This document specifies new "Digital Signature" authentication
method. This method can be used with any types of signatures. As
the authentication methods are not negotiated in the IKEv2, the peer
is only allowed to use this authentication method if the
SIGNATURE_HASH_ALGORITHMS Notify Payload has been sent and received.
In this newly defined authentication method, the Authentication Data
field inside the Authentication Payload does not include only the
signature value, but instead the signature value is prefixed with the
algorithm identification OID. This OID identifies both the signature
algorithm and the hash used when calculating the signature. To make
implementations easier, the OID is prefixed by the 8-bit length
field. This length field allows simple implementations to be able to
know the length of the OID, so they can use it as binary blob which
is compared against the known OIDs, i.e. they do not need to be able
to parse or generate ASN.1 DER OIDs (Note, that the 2nd byte of the
ASN.1 DER OID, also includes the length, but adding it outside makes
things bit easier for implementors).
The OIDs used here are the same OIDs which are used inside the
AlgorithmIdentifier of the PKIX (Section 4.1.1.2 of [RFC5280]), but
only the algorithm OID is included, no parameters etc. The EC curve
is always known by the peer because it needs to have the certificate
or the public key of the other end before it can do signature
verification and public key specifies the curve.
XXX While reading RFC4055, it seemed that the OID is not enough to
specify the hash function used for the RSASSA-PSS, i.e. it seems
that we would need to include full AlgorithmIdentifier ASN object,
as it includes also the parameters, and the hash function is
specified in the parameters. Is my reading of RFC4055 correct?
XXX
The Authentication payload is defined in IKEv2 as follows:
Kivinen Expires June 7, 2013 [Page 4]
Internet-Draft Signature Authentication in IKEv2 December 2012
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Auth Method | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Authentication Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Authentication Payload Format.
o Auth Method (1 octet) - Specifies the method of authentication
used.
Mechanism Value
-----------------------------------------------------------------
Digital Signature <TBD>
Computed as specified in Section 2.15 of RFC5996 using a
private key associated with the public key sent in certificate
payload, and using one of the hash algorithms sent by the other
end in the SIGNATURE_HASH_ALGORITHMS notify payload. If both
ends send and receive SIGNATURE_HASH_ALGORITHMS and signature
authentication is to be used, then this method MUST be used.
The Authentication Data field has bit different format than in
other Authentication methods (see below).
o Authentication Data (variable length) - see Section 2.15 of
RFC5996. For "Digital Signature" format the Authentication data
contains special format as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OID Length | OID (0x06) . OID value len . OID value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ OID value continuing ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Signature Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Authentication Data Format.
Kivinen Expires June 7, 2013 [Page 5]
Internet-Draft Signature Authentication in IKEv2 December 2012
Where the OID Length is the length of the ASN.1 encoded OID value,
and after that is the actual Signature Algorithm OID followed by
the actual signature value. There is no padding between OID and
signature value. ASN.1 encoded OIDs always start with byte of
0x06 followed by the length of the actual OID value (which is
shown in the figure above). For the hash truncation the method of
X9.62, SEC1 and IO 14888-3 MUST be used. XXX Need reference for
X9.62/SEC1 etchere XXX.
4. Hash Algorithm Notification
The supported hash algorithms that can be used for the signature
algorithms are now indicated with new SIGNATURE_HASH_ALGORITHMS
Notification Payload sent inside the IKE_SA_INIT exchange. This
notification also indicates the support of the new signature
algorithm method, i.e sending this notification tells that new
"Digital Signature" authentication method is supported and that
following hash functions are supported by sending peer. Both ends
sends their list of supported hash-algorithms and when calculating
signature a peer MUST pick one algorithm sent by the other peer.
Note, that different algorithms can be used in different directions.
The algorithm OID matching selected hash algorithm (and signature
algorithm) used when calculating the signature is sent inside the
Authentication Data field of the Authentication Payload.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol ID | SPI Size | Notify Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Security Parameter Index (SPI) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Notification Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Notify Payload Format.
Protocol ID is 0, SPI Size 0, and Notify Message Type <TBD from
status types>. The Notification Data value contains list of 16-bit
hash algorithm identifiers from the newly created Hash Algorithm
Identifiers for the IKEv2 IANA registry.
Kivinen Expires June 7, 2013 [Page 6]
Internet-Draft Signature Authentication in IKEv2 December 2012
5. Security Considerations
XXX The text about the guidance how to select suitable hash
functions is missing here. XXX
This new digital signature method does not tie the EC curve to the
specific hash function, which was done in the old IKEv2 ECDSA
methods. This means it is possible to use 512-bit EC curve with
SHA1, i.e. this allows mixing different security levels. This means
that the security of the authentication method is the security of the
weakest of components (signature algorithm, hash algorithm, curve).
This might make the security analysis of the system bit more complex.
Note, that this kind of mixing of the security can be disallowed by
the policy.
The hash algorithm registry does not include MD5 as supported hash
algorithm, as it is not considered safe enough for signature use.
XXX Need reference for MD5 considered unsafe. XXX
The current IKEv2 uses RSASSA-PKCS1-v1_5, and does not allow using
newer padding methods like RSASSA-PSS. This new method allows using
other padding methods.
XXX Need reference for RSASSA-PSS vs RSASSA-PKCS1-v1_5 security.
XXX
The current IKEv2 only allows using normal DSA with SHA-1, which
means the security of the regular DSA is limited to the security of
SHA-1. This new methods allows using longer keys and longer hashes
with DSA.
6. IANA Considerations
This document creates new IANA registry for IKEv2 Hash Algorithms.
Changes and additions to this registry is by expert review.
The initial values of this registry is:
Hash Algorithm Value
-------------- -----
RESERVED 0
SHA1 1
SHA2-256 2
SHA2-384 3
SHA2-512 4
Kivinen Expires June 7, 2013 [Page 7]
Internet-Draft Signature Authentication in IKEv2 December 2012
MD5 is not included to the hash algorithm list as it is not
considered safe enough for signature hash uses.
Values 5-1023 are reserved to IANA. Values 1024-65535 are for
private use among mutually consenting parties.
7. Acknowledgements
Most of this work was based on the work done in the IPsecME design
team for the ECDSA. The design team members were: Dan Harking,
Johannes Merkle, Tero Kivinen, David McGrew, and Yoav Nir.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, 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, May 2008.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
8.2. Informative References
[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,
June 2005.
[RFC5480] Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
"Elliptic Curve Cryptography Subject Public Key
Information", RFC 5480, March 2009.
Appendix A. Examples
Kivinen Expires June 7, 2013 [Page 8]
Internet-Draft Signature Authentication in IKEv2 December 2012
Author's Address
Tero Kivinen
INSIDE Secure
Eerikinkatu 28
HELSINKI FI-00180
FI
Email: kivinen@iki.fi
Kivinen Expires June 7, 2013 [Page 9]