A HMAC function, taking a key as the first argument and the input value as the second, producing a MAC digest.

>>> import qualified Crypto.Hash.SHA256 as SHA256
>>> :t SHA256.hmac
SHA256.hmac :: BS.ByteString -> BS.ByteString -> BS.ByteString
>>> SHA256.hmac "my HMAC key" "my HMAC input"
<256-bit MAC>

Derive a key from a secret, via a HMAC-based key derivation function.

The salt and info arguments are optional to the KDF, and may be simply passed as mempty. An empty salt will be replaced by hashlen zero bytes.

>>> import qualified Crypto.Hash.SHA256 as SHA256
>>> derive SHA256.hmac "my public salt" mempty 64 "my secret input"
<64-byte output keying material>