]>
Signature Authentication in IKEv2INSIDE SecureEerikinkatu 28FI-00180HELSINKIFIkivinen@iki.fi
Security
IP Security Maintenance and Extensions
(ipsecme)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 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 is generic
mechanism, and is not limited to ECDSA, but can also be used with
other signature algorithms.This document adds new IKEv2 ()
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 be preferred instead of PKCS #1
version 1.5 (See section 5 of ). 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 ). The another thing is to add indication
of supported signature hash algorithms by the peer (see ). 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 (RSA, DSA, ECDSA,
RSASSA-PSS, etc), and also allow adding new things in the future
(ECGDSA, ElGamal etc). For this the signature algorithm is
specified in the same way as the PKIX ()
specifies the signature of the Certificate, i.e. there is simple
ASN.1 object before the actual signature data. This ASN.1 object
contains the OID specifying the algorithm, and associated
parameters to it. In normal case the IKEv2 implementations
supports fixed amount of signature methods, with commonly used
parameters, so it is acceptable for the implementation to just
treat this ASN.1 object as binary blob which is compared against
the known values, or the implementation can parse the ASN.1 and
extract information from there.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
.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 ASN.1 object containing the algorithm used to generate
the signature. The ASN.1 object contains the algorithm
identification OID, and this OID identifies both the signature
algorithm and the hash used when calculating the signature. In
addition to the OID there is optional parameters which might be
needed for algorithms like RSASSA-PSS.To make implementations easier, the ASN.1 object is prefixed by
the 8-bit length field. This length field allows simple
implementations to be able to know the length of the ASN.1 without
the need to parse it, so they can use it as binary blob which is
compared against the known signature algorithm ASN.1 objects, i.e.
they do not need to be able to parse or generate ASN.1 objects.
See for commonly used ASN.1
objects.The ASN.1 used here are the same ASN.1 which is used in the
AlgorithmIdentifier of the PKIX (Section 4.1.1.2 of ). The algorithm OID inside the ASN.1 specifies
the signature algorithm and the hash function, which are needed to
signature verification. 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.Currently only the RSASSA-PSS uses the parameters, for all
others the parameters is either NULL or missing. Note, that for
some algorithms there is two possible ASN.1 encoding possible, one
with parameters being NULL and others where the whole parameters
is omitted. This is because some of those algorithms are specified
that way. When encoding the ASN.1 implementations should use the
preferred way, i.e. if the algorithm specification says
"preferredPresent" then parameter object needs to be there (i.e.
it will be NULL if no parameters is specified), and if it says
"preferredAbsent", then the whole parameters object is missing.The Authentication payload is defined in IKEv2 as follows:Auth Method (1 octet) - Specifies the method of
authentication used.
Authentication Data (variable length) - see Section 2.15 of
RFC5996. For "Digital Signature" format the Authentication data
contains special format as follows:
Where the ASN.1 Length is the length of the ASN.1 encoded
AlgorithmIdentifier object, and after that is the actual
AlgorithmIdentifier ASN.1 object, followed by the actual signature
value. There is no padding between ASN.1 object and signature
value.
For the hash truncation the method of X9.62 () MUST be used.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.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.The "Recommendations for Key Management" () 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 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 ().The current IKEv2 uses RSASSA-PKCS1-v1_5, which do have some
problems (, ) and does
not allow using newer padding methods like RSASSA-PSS. This new
method allows using other padding methods.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.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: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.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.
&rfc2119;
&rfc5280;
&rfc5996;
&rfc3279;
&rfc4055;
&rfc5480;
&rfc5758;
&rfc5912;
How to break MD5 and other hash functionsVariants of Bleichenbacher's Low-Exponent Attack on PKCS#1 RSA SignaturesRecommendations for Key ManagementPublic Key Cryptography for the Financial
Services Industry: The Elliptic Curve Digital Signature
Algorithm (ECDSA)American National Standards
InstituteEvaluation of Security Level of Cryptography: RSA-OAEP,
RSA-PSS, RSA SignatureUniversity of WaterlooThis section lists commonly used ASN.1 objects in binary form.
This section is not-normative, and these values should only be
used as examples, i.e. if this and the actual specification of the
algorithm ASN.1 object is different the actual format specified in
the actual specification needs to be used. These values are taken
form the New ASN.1 Modules for the Public Key Infrastructure Using
X.509 ().These algorithm identifiers here include several different
ASN.1 objects with different hash algorithms. In this document
we only include the commonly used ones i.e. the one using SHA-1,
or SHA-2 as hash function. Some of those other algorithms (MD2,
MD5) specified for this are not safe enough to be used as
signature hash algorithm, and some are omitted as there is no
hash algorithm specified in the our IANA registry for them.
Note, that there is no parameters in any of these, but all
specified here needs to have NULL parameters present in the
ASN.1.See Algorithms and Identifiers for PKIX Profile () and Additional Algorithms and Identifiers for
RSA Cryptography for PKIX Profile () 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.XXX binary object missingsha256WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 11 }Parameters are required, and they must be NULL.XXX binary object missingsha384WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 12 }Parameters are required, and they must be NULL.XXX binary object missingsha512WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 13 }Parameters are required, and they must be NULL.XXX binary object missingWith different DSA algorithms the parameters are always
omitted. Again we omit dsa-with-sha224 as there is no hash
algorithm in our IANA registry for it.See Algorithms and Identifiers for PKIX Profile () and PKIX Additional Algorithms and
Identifiers for DSA and ECDSA ( for more
information.dsa-with-sha1 OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) x9-57(10040) x9algorithm(4) 3 }Parameters are absent.XXX binary object missingdsa-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.XXX binary object missingWith different ECDSA algorithms the parameters are always
omitted. Again we omit ecdsa-with-sha224 as there is no hash
algorithm in our IANA registry for it.See Elliptic Curve Cryptography Subject Public Key
Information (), Algorithms and
Identifiers for PKIX Profile () and PKIX
Additional Algorithms and Identifiers for DSA and ECDSA ( 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.XXX binary object missingecdsa-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.XXX binary object missingecdsa-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.XXX binary object missingecdsa-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.XXX binary object missingWith the RSASSA-PSS the algorithm object identifier is always
id-RSASSA-PSS, but the hash function is taken from the
parameters, and it is required. See for
more information.id-RSASSA-PSS OBJECT IDENTIFIER ::= { pkcs-1 10 }Parameters are empty, but the ASN.1 part of the sequence
must be there. This means default parameters are used (same as
the next example).XXX binary object missingid-RSASSA-PSS OBJECT IDENTIFIER ::= { pkcs-1 10 }Here the parameters are present, and contains the default
parameters, i.e. SHA-1, mgf1SHA1, saltlength of 20,
trailerfield of 1.XXX binary object missing