| IP Security Maintenance and Extensions (ipsecme) | T. Kivinen |
| Internet-Draft | INSIDE Secure |
| Updates: RFC 5996 (if approved) | J. Snyder |
| Intended status: Standards Track | Opus One |
| Expires: January 22, 2015 | July 21, 2014 |
Signature Authentication in IKEv2
draft-kivinen-ipsecme-signature-auth-07.txt
The Internet Key Exchange Version 2 (IKEv2) protocol has limited support for the Elliptic Curve Digital Signature Algorithm (ECDSA). The current version only includes support for three Elliptic Curve groups, and there is a fixed hash algorithm tied to each group. This document generalizes IKEv2 signature support to allow any signature method supported by the PKIX and also adds signature hash algorithm negotiation. This is a generic mechanism, and is not limited to ECDSA, but can also be used with other signature algorithms.
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This document adds a new IKEv2 ([RFC5996]) authentication method to support signature methods in a more general way. The current signature-based authentication methods in 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 is cumbersome when more signature algorithms, hash algorithms and elliptic curves need to be supported:
With the selection of SHA-3, it might be possible that a signature method can be used with either SHA-3 or SHA-2. This means that a new mechanism for negotiating the hash algorithm for a signature algorithm is needed.
This document specifies two things:
The new digital signature method is flexible enough to include all current signature methods (RSA, DSA, ECDSA, RSASSA-PSS, etc.), and add new methods (ECGDSA, ElGamal, etc.) in the future. To support this flexibility, the signature algorithm is specified in the same way that PKIX ([RFC5280]) specifies the signature of the Digital Certificate, by placing a simple ASN.1 object before the actual signature data. This ASN.1 object contains an OID specifying the algorithm and associated parameters. When an IKEv2 implementation supports a fixed set of signature methods with commonly used parameters, it is acceptable for the implementation to treat the ASN.1 object as a binary blob which can be compared against the fixed set of known values. IKEv2 implementations can also parse the ASN.1 and extract the signature algorithm and associated parameters.
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].
This document specifies a new "Digital Signature" authentication method. This method can be used with any type of signature. As the authentication methods are not negotiated in IKEv2, the peer is only allowed to use this authentication method if the Notify payload of type SIGNATURE_HASH_ALGORITHMS has been sent and received by each peer.
In this authentication method, the Authentication Data field inside the Authentication Payload does not just include the signature value, as do other existing IKEv2 Authentication Payloads. Instead, the signature value is prefixed with an ASN.1 object indicating the algorithm used to generate the signature. The ASN.1 object contains the algorithm identification OID, which identifies both the signature algorithm and the hash used when calculating the signature. In addition to the OID, the ASN.1 object can contain optional parameters which might be needed for algorithms such as RSASSA-PSS (Section 8.1 of [RFC3447]).
To make implementations easier, the ASN.1 object is prefixed by the 8-bit length field. This length field allows simple implementations to know the length of the ASN.1 object without the need to parse it, so they can use it as a binary blob to be compared against known signature algorithm ASN.1 objects. Thus, simple implementations may not need to be able to parse or generate ASN.1 objects. See Appendix A for commonly used ASN.1 objects.
The ASN.1 used here is the same ASN.1 used in the AlgorithmIdentifier of PKIX (Section 4.1.1.2 of [RFC5280]), encoded using distinguished encoding rules (DER) [CCITT.X690.2002]. The algorithm OID inside the ASN.1 specifies the signature algorithm and the hash function, both of which are needed for signature verification.
Currently, only the RSASSA-PSS signature algorithm uses the optional parameters. For other signature algorithms, the parameters are either NULL or missing. Note, that for some algorithms there are two possible ASN.1 encodings, one with optional parameters included but set to NULL and the other where the optional parameters are omitted. These dual encodings exist because of the way those algorithms are specified. When encoding the ASN.1, implementations SHOULD use the preferred format called for by the algorithm specification. If the algorithm specification says "preferredPresent" then the parameters object needs to be present, although it will be NULL if no parameters are specified. If the algorithm specification says "preferredAbsent", then the entire optional parameters object is missing.
The Authentication payload is defined in IKEv2 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Payload |C| RESERVED | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Auth Method | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Authentication Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Authentication Payload Format.
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 the
Certificate payload, and using one of the hash algorithms
sent by the other end in the Notify payload of type
SIGNATURE_HASH_ALGORITHMS. If both ends send and receive
SIGNATURE_HASH_ALGORITHMS Notify payloads and signature
authentication is to be used, then the authentication
method specified in this Authentication payload MUST be
used. The format of the Authentication Data field is
different from other Authentication methods and is
specified 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASN.1 Length | AlgorithmIdentifier ASN.1 object |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ AlgorithmIdentifier ASN.1 object continuing ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Signature Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Authentication Data Format.
There is no padding between ASN.1 object and signature value. For hash truncation, the method specified in ANSI X9.62:2005 (
[X9.62]) MUST be used.The supported hash algorithms that can be used for the signature algorithms are indicated with a Notify payload of type SIGNATURE_HASH_ALGORITHMS sent inside the IKE_SA_INIT exchange.
This notification also implicitly indicates support of the new "Digital Signature" algorithm method, as well as the list of hash functions supported by the sending peer.
Both ends send their list of supported hash algorithms. When calculating the digital 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 indicating the selected hash algorithm (and signature algorithm) used when calculating the signature is sent inside the Authentication Data field of the Authentication payload (with Auth Method of "Digital Signature" as defined above).
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.
The Notify payload format is defined in RFC5996 section 3.10. When a Notify payload of type SIGNATURE_HASH_ALGORITHMS is sent, the Protocol ID field is set to 0, the SPI Size is set to 0, and the Notify Message Type is set to <TBD from status types>.
The Notification Data field contains the list of 16-bit hash algorithm identifiers from the Hash Algorithm Identifiers for the IKEv2 IANA registry. There is no padding between the hash algorithm identifiers.
This specification does not provide a way for the peers to indicate the public / private key pair types they have. This raises the question of how the responder selects a public / private key pair type that the initiator supports. This information can be found by several methods.
One method to signal the key the initiator wants the responder to use is to indicate that in the IDr payload of the IKE_AUTH request sent by the initiator. In this case, the initiator indicates that it wants the responder to use a particular public / private key pair by sending an IDr payload which indicates that information. In this case, the responder has different identities configured, with each of those identities associated to a public / private key or key type.
Another method to ascertain the key the initiator wants the responder to use is through a Certificate Request payload sent by the initiator. For example, the initiator could indicate in the Certificate Request payload that it trusts a CA signed by an ECDSA key. This indication implies that the initiator can process ECDSA signatures, which means that the responder can safely use ECDSA keys when authenticating.
A third method is for the responder to check the key type used by the initiator, and use same key type that the initiator used. This method does not work if the initiator is using shared secret or EAP authentication (i.e., is not using public keys). If the initiator is using public key authentication, this method is the best way for the responder to ascertain the type of key the initiator supports.
If the initiator uses a public key type that the responder does not support, the responder replies with a Notify message with error type AUTHENTICATION_FAILED. If the initiator has multiple different keys, it may try a different key (and perhaps a different key type) until it finds a key that the other end accepts. The initiator can also use the Certificate Request payload sent by the responder to help decide which public key should be tried. In normal cases, when the initiator has multiple public keys, out-of-band configuration is used to select a public key for each connection.
The "Recommendations for Key Management" ([NIST800-57]) table 2 combined with table 3 gives recommendations for how to select suitable hash functions for the signature.
This new digital signature method does not tie the Elliptic Curve to a specific hash function, which was done in the old IKEv2 ECDSA methods. This means it is possible to mix different security levels. For example, it is possible to use 512-bit Elliptic Curve with SHA1. This means that the security of the authentication method is the security of the weakest component (signature algorithm, hash algorithm, or curve). This complicates the security analysis of the system.
IKEv2 peers have a series of policy databases (see [RFC4301] section 4.4 "Major IPsec Databases") that define which security algorithms and methods should be used during establishment of security associations. To help end-users select the desired security levels for communications protected by IPsec, implementers may wish to provide a mechanism in the IKE policy databases to limit the mixing of security levels or to restrict combinations of protocols.
Security downgrade attacks, where more secure methods are deleted or modified from a payload by a Man-in-the-Middle to force lower levels of security, are not a significant concern in IKEv2 Authentication Payloads as discussed in this RFC. This is because a modified AUTH payload will be detected when the peer computes a signature over the IKE messages.
One specific class of downgrade attacks requires selection of catastrophically weak ciphers. In this type of attack, the Man-in-the-Middle attacker is able to "break" the cryptography in real time. This type of downgrade attack should be blocked by policy regarding cipher algorithm selection, as discussed above.
The hash algorithm registry does not include MD5 as a supported hash algorithm, as it is not considered safe enough for signature use ([WY05]).
The current IKEv2 protocol uses RSASSA-PKCS1-v1_5, which has known security vulnerabilities ([KA08], [ME01]) and does not allow using newer padding methods such as RSASSA-PSS. The new method described in this RFC allows using other padding methods.
The current IKEv2 protocol only allows use of normal DSA with SHA-1, which means the security of the authentication is limited to the security of SHA-1. This new method allows using longer keys and longer hashes with DSA.
This document creates a new IANA registry for IKEv2 Hash Algorithms. Changes and additions to this registry are by expert review.
The initial values of this registry are:
Hash Algorithm Value -------------- ----- RESERVED 0 SHA1 1 SHA2-256 2 SHA2-384 3 SHA2-512 4
MD5 is not included in 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.
This specification also adds one new "IKEv2 Notify Message Types - Status Types" value for SIGNATURE_HASH_ALGORITHMS, and adds one new "IKEv2 Authentication Method" value for "Digital Signature".
Most of this work was based on the work done in the IPsecME design team for the ECDSA. The design team members were: Dan Harkins, Johannes Merkle, Tero Kivinen, David McGrew, and Yoav Nir.
| [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. |
This section lists commonly used ASN.1 objects in binary form. This section is not normative, and these values should only be used as examples. If the ASN.1 object listed in Appendix A and the ASN.1 object specified by the algorithm differ, then the algorithm specification must be used. These values are taken from "New ASN.1 Modules for the Public Key Infrastructure Using X.509 (PKIX)" ([RFC5912]).
The algorithm identifiers here include several different ASN.1 objects with different hash algorithms. This document only includes the commonly used ones, i.e. the ones using SHA-1 or SHA-2 as hash function. Some other algorithms (such as MD2 and MD5) are not safe enough to be used as signature hash algorithms, and are omitted. The IANA registry does not have code points for these other algorithms with RSA Encryption. Note that there are no optional parameters in any of these algorithm identifiers, but all included here need NULL optional parameters present in the ASN.1.
See "Algorithms and Identifiers for PKIX Profile" ([RFC3279]) and "Additional Algorithms and Identifiers for RSA Cryptography for use in PKIX Profile" ([RFC4055]) for more information.
sha1WithRSAEncryption OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 5 }
Parameters are required, and they must be NULL.
Name = sha1WithRSAEncryption, oid = 1.2.840.113549.1.1.5 Length = 15 0000: 300d 0609 2a86 4886 f70d 0101 0505 00
sha256WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 11 }
Parameters are required, and they must be NULL.
Name = sha256WithRSAEncryption, oid = 1.2.840.113549.1.1.11 Length = 15 0000: 300d 0609 2a86 4886 f70d 0101 0b05 00
sha384WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 12 }
Parameters are required, and they must be NULL.
Name = sha384WithRSAEncryption, oid = 1.2.840.113549.1.1.12 Length = 15 0000: 300d 0609 2a86 4886 f70d 0101 0c05 00
sha512WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 13 }
Parameters are required, and they must be NULL.
Name = sha512WithRSAEncryption, oid = 1.2.840.113549.1.1.13 Length = 15 0000: 300d 0609 2a86 4886 f70d 0101 0d05 00
With DSA algorithms, optional parameters are always omitted. Only algorithm combinations for DSA listed in the IANA registry are included.
See "Algorithms and Identifiers for PKIX Profile" ([RFC3279]) and "PKIX Additional Algorithms and Identifiers for DSA and ECDSA" ([RFC5758] for more information.
dsa-with-sha1 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) x9-57(10040) x9algorithm(4) 3 }
Parameters are absent.
Name = dsa-with-sha1, oid = 1.2.840.10040.4.3 Length = 11 0000: 3009 0607 2a86 48ce 3804 03
dsa-with-sha256 OBJECT IDENTIFIER ::= { joint-iso-ccitt(2) country(16) us(840) organization(1) gov(101) csor(3) algorithms(4) id-dsa-with-sha2(3) 2 }
Parameters are absent.
Name = dsa-with-sha256, oid = 2.16.840.1.101.3.4.3.2 Length = 13 0000: 300b 0609 6086 4801 6503 0403 02
With ECDSA algorithms, the optional parameters are always omitted. Only algorithm combinations for ECDSA listed in the IANA registry are included.
See "Elliptic Curve Cryptography Subject Public Key Information" ([RFC5480]), "Algorithms and Identifiers for PKIX Profile" ([RFC3279]) and "PKIX Additional Algorithms and Identifiers for DSA and ECDSA" ([RFC5758] for more information.
ecdsa-with-SHA1 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) ansi-X9-62(10045) signatures(4) 1 }
Parameters are absent.
Name = ecdsa-with-sha1, oid = 1.2.840.10045.4.1 Length = 11 0000: 3009 0607 2a86 48ce 3d04 01
ecdsa-with-SHA256 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 2 }
Parameters are absent.
Name = ecdsa-with-sha256, oid = 1.2.840.10045.4.3.2 Length = 12 0000: 300a 0608 2a86 48ce 3d04 0302
ecdsa-with-SHA384 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 3 }
Parameters are absent.
Name = ecdsa-with-sha384, oid = 1.2.840.10045.4.3.3 Length = 12 0000: 300a 0608 2a86 48ce 3d04 0303
ecdsa-with-SHA512 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 4 }
Parameters are absent.
Name = ecdsa-with-sha512, oid = 1.2.840.10045.4.3.4 Length = 12 0000: 300a 0608 2a86 48ce 3d04 0304
With RSASSA-PSS, the algorithm object identifier must always be id-RSASSA-PSS, and the hash function and padding parameters are conveyed in the parameters (which are not optional in this case). See [RFC4055] for more information.
id-RSASSA-PSS OBJECT IDENTIFIER ::= { pkcs-1 10 }
Parameters are empty, but the ASN.1 part of the sequence must be present. This means default parameters are used.
0000 : SEQUENCE 0002 : OBJECT IDENTIFIER RSASSA-PSS (1.2.840.113549.1.1.10) 000d : SEQUENCE
Length = 15 0000: 300d 0609 2a86 4886 f70d 0101 0a30 00
id-RSASSA-PSS OBJECT IDENTIFIER ::= { pkcs-1 10 }
Here the parameters are present, and contain the default parameters, i.e. hashAlgorithm of SHA-1, maskGenAlgorithm of mgf1SHA1, saltLength of 20, trailerField of 1.
0000 : SEQUENCE 0002 : OBJECT IDENTIFIER RSASSA-PSS (1.2.840.113549.1.1.10) 000d : SEQUENCE 000f : CONTEXT 0 0011 : SEQUENCE 0013 : OBJECT IDENTIFIER id-sha1 (1.3.14.3.2.26) 001a : NULL 001c : CONTEXT 1 001e : SEQUENCE 0020 : OBJECT IDENTIFIER 1.2.840.113549.1.1.8 002b : SEQUENCE 002d : OBJECT IDENTIFIER id-sha1 (1.3.14.3.2.26) 0034 : NULL 0036 : CONTEXT 2 0038 : INTEGER 0x14 (5 bits) 003b : CONTEXT 3 003d : INTEGER 0x1 (1 bits)
Name = RSASSA-PSS with default parameters,
oid = 1.2.840.113549.1.1.10
Length = 64
0000: 303e 0609 2a86 4886 f70d 0101 0a30 31a0
0010: 0b30 0906 052b 0e03 021a 0500 a118 3016
0020: 0609 2a86 4886 f70d 0101 0830 0906 052b
0030: 0e03 021a 0500 a203 0201 14a3 0302 0101
id-RSASSA-PSS OBJECT IDENTIFIER ::= { pkcs-1 10 }
Here the parameters are present, and contain hashAlgorithm of SHA-256, maskGenAlgorithm of SHA-256, saltLength of 32, trailerField of 1.
0000 : SEQUENCE 0002 : OBJECT IDENTIFIER RSASSA-PSS (1.2.840.113549.1.1.10) 000d : SEQUENCE 000f : CONTEXT 0 0011 : SEQUENCE 0013 : OBJECT IDENTIFIER id-sha256 (2.16.840.1.101.3.4.2.1) 001e : NULL 0020 : CONTEXT 1 0022 : SEQUENCE 0024 : OBJECT IDENTIFIER 1.2.840.113549.1.1.8 002f : SEQUENCE 0031 : OBJECT IDENTIFIER id-sha256 (2.16.840.1.101.3.4.2.1) 003c : NULL 003e : CONTEXT 2 0040 : INTEGER 0x20 (6 bits) 0043 : CONTEXT 3 0045 : INTEGER 0x1 (1 bits)
Name = RSASSA-PSS with sha-256, oid = 1.2.840.113549.1.1.10 Length = 72 0000: 3046 0609 2a86 4886 f70d 0101 0a30 39a0 0010: 0f30 0d06 0960 8648 0165 0304 0201 0500 0020: a11c 301a 0609 2a86 4886 f70d 0101 0830 0030: 0d06 0960 8648 0165 0304 0201 0500 a203 0040: 0201 20a3 0302 0101
The IKEv2 AUTH payload would start like this:
00000000: NN00 00LL XX00 0000 0f30 0d06 092a 8648 00000010: 86f7 0d01 0105 0500 ....
Where the NN will be the next payload type (i.e. the value depends on the next payload after this Authentication payload), the LL will be the length of this payload, and after the sha1WithRSAEncryption ASN.1 block (15 bytes) there will be the actual signature, which is omitted here.
Note to the RFC editor / IANA, replace the XX above with the newly allocated authentication method type for Digital Signature, and remove this note.