Struct LengthBounds 

pub struct LengthBounds;

Type that is used to bound the implementations to valid key and output lengths.

We implement SupportsKeyLen and SupportsOutLen for Blake2s<LengthBounds> and Blake2b<LengthBounds> with the appropriate lengths. This can be used by callers to bound their own implementations to only accept valid lengths.

Example

use libcrux_blake2::{Blake2b, Blake2bBuilder, LengthBounds, SupportsKeyLen, SupportsOutLen};

// A function that does a keyed Blake2b and only accepts valid key lengths
fn keyed_hash<const KEY_LEN: usize>(key: &[u8; KEY_LEN], msg: &[u8]) -> [u8; 32]
where
    Blake2b<LengthBounds>: SupportsKeyLen<KEY_LEN>,
{
    let mut hasher = Blake2bBuilder::new_keyed_const(key)
        .build_const_digest_len::<32>();
    hasher.update(msg);
    let mut output = [0u8; 32];
    hasher.finalize(&mut output);
    output
}

// This compiles because Blake2b supports 32 byte keys
let key = [0; 32]; // this should actually be random
let msg = b"a test message";
let result = keyed_hash(&key, msg);