Blake2 rework

[newpavlov]

Rework of blake2 crate based on blake2-rfc. (with the consent of Cesar)

[Ralith]

I relied on 0.3.0's support for statically customized hash output size (specifically, I use a 200-bit hash because it divides evenly into both bytes and base 36). This seems to break my use case.

[newpavlov]

BLAKE2 defines variable size output as a simple truncation, so this code from compiler perspective will behave identically to the old approach:

use blake2::Blake2b;
use digest::{Digest, VariableOutput};

let hasher = Blake2b::new();
// do hashing
let hash = [0u8; 200];
hasher.variable_result(&mut hash[..]);

[Ralith]

Thanks! However, doesn't the 0.3.0 code place the output size in the parameter block, as specified in the RFC? It seems like the new approach would be non-conformant and yield different hashes.

[newpavlov]

Oh... It indeed looks like my mistake and overlook while reworking the crate. Thank you for noticing this!

I will try fix this issue until the end of the week.

[Ralith]

Thanks! No particular urgency, since 0.3.0 is still working fine for me and I can always construct a parameter block manually if I really need to, but it's good to know support is intended.