On 12/9/24 19:43, Peter Dimov via Boost wrote:
Note that this is not the only innovation that the proposed hash algorithm concept involves. All hash algorithms are required to support seeding from uint64_t and from an arbitrary sequence of bytes, which makes them effectively _keyed hash functions_ (or _message authentication codes_).
Also note that the requirement that one can interleave calls to `update` and `result` arbitrarily makes it possible to implement byte sequence seeding (for algorithms that don't already support it) in the following manner:
Hash::Hash( unsigned char const* p, size_t n ): Hash() { if( n != 0 ) { update( p, n ); result(); } }
Subsequent `update` calls now start from an initial internal state that has incorporated the contents of [p, p+n), and that has been "finalized" (scrambled thoroughly) such that the result is not equivalent to just prepending the seed to the message (as would have happened if the result() call has been omitted.)
Also, my understanding of HMAC[1] is that the key is prepended to the subsequent data and then the whole data is hashed. This contradicts with your code calling result() in the middle. Am I missing something? [1]: https://datatracker.ietf.org/doc/html/rfc2104#section-2