Hi,

I need a keyed hash function (HMAC) based on SHA256.  I looked at Cryptokit's
support for HMAC, and though it has built-in support for HMAC-MD5 and HMAC-SHA1,
it seems HMAC-SHA256 is not directly supported, despite Cryptokit implementing
the SHA256 algorithm.

While RFC 2104 seems straightforward enough and there's always the option
of adapting Cryptokit's HMAC-SHA1 code, I wonder if someone else out there
either a) has already done this, or b) knows of an alternative library
implementing HMAC-SHA256.

Best regards,
Dario Teixeira