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|
-- |
-- Module : Crypto.KDF.HKDF
-- License : BSD-style
-- Maintainer : Vincent Hanquez <vincent@snarc.org>
-- Stability : experimental
-- Portability : unknown
--
-- Key Derivation Function based on HMAC
--
-- See RFC5869
--
{-# LANGUAGE BangPatterns #-}
module Crypto.KDF.HKDF
( PRK
, extract
, extractSkip
, expand
) where
import Data.Word
import Crypto.Hash
import Crypto.MAC.HMAC
import Crypto.Internal.ByteArray (ScrubbedBytes, ByteArray, ByteArrayAccess)
import qualified Crypto.Internal.ByteArray as B
-- | Pseudo Random Key
data PRK a = PRK (HMAC a) | PRK_NoExpand ScrubbedBytes
deriving (Eq)
instance ByteArrayAccess (PRK a) where
length (PRK hm) = B.length hm
length (PRK_NoExpand sb) = B.length sb
withByteArray (PRK hm) = B.withByteArray hm
withByteArray (PRK_NoExpand sb) = B.withByteArray sb
-- | Extract a Pseudo Random Key using the parameter and the underlaying hash mechanism
extract :: (HashAlgorithm a, ByteArrayAccess salt, ByteArrayAccess ikm)
=> salt -- ^ Salt
-> ikm -- ^ Input Keying Material
-> PRK a -- ^ Pseudo random key
extract salt ikm = PRK $ hmac salt ikm
-- | Create a PRK directly from the input key material.
--
-- Only use when guaranteed to have a good quality and random data to use directly as key.
-- This effectively skip a HMAC with key=salt and data=key.
extractSkip :: ByteArrayAccess ikm
=> ikm
-> PRK a
extractSkip ikm = PRK_NoExpand $ B.convert ikm
-- | Expand key material of specific length out of the parameters
expand :: (HashAlgorithm a, ByteArrayAccess info, ByteArray out)
=> PRK a -- ^ Pseudo Random Key
-> info -- ^ Optional context and application specific information
-> Int -- ^ Output length in bytes
-> out -- ^ Output data
expand prkAt infoAt outputLength =
let hF = hFGet prkAt
in B.concat $ loop hF B.empty outputLength 1
where
hFGet :: (HashAlgorithm a, ByteArrayAccess b) => PRK a -> (b -> HMAC a)
hFGet prk = case prk of
PRK hmacKey -> hmac hmacKey
PRK_NoExpand ikm -> hmac ikm
info :: ScrubbedBytes
info = B.convert infoAt
loop :: HashAlgorithm a
=> (ScrubbedBytes -> HMAC a)
-> ScrubbedBytes
-> Int
-> Word8
-> [ScrubbedBytes]
loop hF tim1 n i
| n <= 0 = []
| otherwise =
let input = B.concat [tim1,info,B.singleton i] :: ScrubbedBytes
ti = B.convert $ hF input
hashLen = B.length ti
r = n - hashLen
in (if n >= hashLen then ti else B.take n ti)
: loop hF ti r (i+1)
|
