Hmac constructor
Create an Hmac object from a Hash and a binary key.
The key should be a secret shared between the sender and receiver of the message.
Implementation
Hmac(Hash hash, List<int> key)
: _hash = hash,
_key = Uint8List(hash.blockSize) {
// Hash the key if it's longer than the block size of the hash.
if (key.length > _hash.blockSize) key = _hash.convert(key).bytes;
// If [key] is shorter than the block size, the rest of [_key] will be
// 0-padded.
_key.setRange(0, key.length, key);
}