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-- Copyright 2018 Google LLC
--
-- Licensed under the Apache License, Version 2.0 (the "License"); you may not
-- use this file except in compliance with the License. You may obtain a copy of
-- the License at
--
-- https://www.apache.org/licenses/LICENSE-2.0
--
-- Unless required by applicable law or agreed to in writing, software
-- distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
-- WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
-- License for the specific language governing permissions and limitations under
-- the License.
module Codec.Crypto.HKDF
( AssociatedData(AssociatedData), Salt(Salt), SecretKey(SecretKey), noSalt
, hkdf, extract, expand
) where
import qualified Data.ByteString as ByteString
import qualified Data.ByteString.Unsafe as ByteString
import Foreign (allocaArray)
import Foreign.Marshal.Unsafe (unsafeLocalState)
import BTLS.BoringSSL.Digest (evpMaxMDSize)
import BTLS.BoringSSL.HKDF
import BTLS.BoringSSLPatterns (onBufferOfMaxSize)
import BTLS.Cast (asCUCharBuf)
import BTLS.Types
( Algorithm(Algorithm), AssociatedData(AssociatedData), Salt(Salt)
, SecretKey(SecretKey), noSalt
)
-- | Computes an HKDF as specified by RFC 5869.
hkdf :: Algorithm -> Salt -> AssociatedData -> Int -> SecretKey -> SecretKey
hkdf md salt info outLen = expand md info outLen . extract md salt
-- | Computes an HKDF pseudorandom key (PRK) as specified by RFC 5869.
extract :: Algorithm -> Salt -> SecretKey -> SecretKey
extract (Algorithm md) (Salt salt) (SecretKey secret) =
SecretKey $
unsafeLocalState $
onBufferOfMaxSize evpMaxMDSize $ \pOutKey pOutLen -> do
-- @HKDF_extract@ won't mutate @secret@ or @salt@, so the sharing inherent
-- in 'ByteString.unsafeUseAsCStringLen' is fine.
ByteString.unsafeUseAsCStringLen secret $ \(pSecret, secretLen) ->
ByteString.unsafeUseAsCStringLen salt $ \(pSalt, saltLen) ->
hkdfExtract
(asCUCharBuf pOutKey) pOutLen
md
(asCUCharBuf pSecret) (fromIntegral secretLen)
(asCUCharBuf pSalt) (fromIntegral saltLen)
-- | Computes HKDF output key material (OKM) as specified by RFC 5869.
expand :: Algorithm -> AssociatedData -> Int -> SecretKey -> SecretKey
expand (Algorithm md) (AssociatedData info) outLen (SecretKey secret) =
SecretKey $
unsafeLocalState $
allocaArray outLen $ \pOutKey -> do
-- @HKDF_expand@ won't mutate @secret@ or @info@, so the sharing inherent
-- in 'ByteString.unsafeUseAsCStringLen' is fine.
ByteString.unsafeUseAsCStringLen secret $ \(pSecret, secretLen) ->
ByteString.unsafeUseAsCStringLen info $ \(pInfo, infoLen) ->
hkdfExpand
(asCUCharBuf pOutKey) (fromIntegral outLen)
md
(asCUCharBuf pSecret) (fromIntegral secretLen)
(asCUCharBuf pInfo) (fromIntegral infoLen)
ByteString.packCStringLen (pOutKey, outLen)
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