[gnutls-devel] Supported MAC algorithms

[Jaak Ristioja]

On 22.12.2015 11:35, Nikos Mavrogiannopoulos wrote:
> On Mon, 2015-12-21 at 14:50 +0200, Jaak Ristioja wrote:
>> Hello!
>> The table of supported HMAC algorithms in the GnuTLS manual only
>> lists
>> MAC_MD5, MAC_SHA1, MAC_SHA256 and MAC_AEAD, whereas the enum
>> gnutls_mac_algorithm_t in gnutls.h also lists GNUTLS_MAC_SHA384,
>> GNUTLS_MAC_SHA512, GNUTLS_MAC_SHA224 etc. Are these HMAC algorithms
>> really not supported or is the documentation incorrect?
> 
> Hi Jaak,
>  This table lists the algorithms supported in the TLS protocol. SHA224
> and SHA512 are not supported. SHA384 is supported by some ciphersuites
> and is indeed missing.
> 
>> The GnuTLS documentation doesn't clearly state whether the HMAC
>> implementations in GnuTLS are based on RFC 2104?
> 
> Why would that matter? This section describes the algorithms used in
> TLS, so it should be apparent that the HMAC construction used is the
> one referenced by TLS. If that's not sufficient, please suggest some
> text.

I think it is confusing that subsection "8.3 Hash and HMAC functions"
which refers to the Table 3.2 of the supported HMAC algorithms with is
under section "8 Using GnuTLS as a cryptographic library" which I think
is rather TLS-agnostic. I think subsection 8.3 should have a separate
table listing all the algorithms supported by GnuTLS as a cryptographic
library, whereas the description of Table 3.2 should state "Supported
MAC algorithms in the TLS record layer" and the second paragraph under
3.3.1 should also be corrected accordingly.

Best regards,
Jaak