string2key utility function

Interpret the S2K systems, modulo the actual hashing.

1 files changed, 22 insertions, 0 deletions

diff --git a/Data/OpenPGP.hs b/Data/OpenPGP.hs
index e71e48a..9a50fa0 100644
--- a/Data/OpenPGP.hs
+++ b/Data/OpenPGP.hs
@@ -50,6 +50,7 @@ module Data.OpenPGP (
         Message(..),
         SignatureSubpacket(..),
         S2K(..),
+        string2key,
         HashAlgorithm(..),
         KeyAlgorithm(..),
         SymmetricAlgorithm(..),
@@ -71,6 +72,7 @@ import Data.Word
 import Data.Char
 import Data.List
 import Data.OpenPGP.Internal
+import qualified Data.ByteString as BS
 import qualified Data.ByteString.Lazy as LZ
 
 #ifdef CEREAL
@@ -735,6 +737,26 @@ instance BINARY_CLASS S2K where
                         3 -> IteratedSaltedS2K <$> get <*> get <*> (decode_s2k_count <$> get)
                         _ -> S2K t <$> getRemainingByteString
 
+-- | Take a hash function and an 'S2K' value and generate the bytes
+--   needed for creating a symmetric key.
+--
+-- Return value is always infinite length.
+-- Take the first n bytes you need for your keysize.
+string2key :: (HashAlgorithm -> LZ.ByteString -> BS.ByteString) -> S2K -> LZ.ByteString -> LZ.ByteString
+string2key hsh (SimpleS2K halgo) s = infiniHashes (hsh halgo) s
+string2key hsh (SaltedS2K halgo salt) s =
+        infiniHashes (hsh halgo) (encode salt `LZ.append` s)
+string2key hsh (IteratedSaltedS2K halgo salt count) s =
+        infiniHashes (hsh halgo) $
+        LZ.take (max (fromIntegral count) (LZ.length s))
+        (LZ.cycle $ encode salt `LZ.append` s)
+string2key _ s2k _ = error $ "Unsupported S2K specifier: " ++ show s2k
+
+infiniHashes :: (LZ.ByteString -> BS.ByteString) -> LZ.ByteString -> LZ.ByteString
+infiniHashes hsh s = LZ.fromChunks (hs 0)
+        where
+        hs c = hsh (LZ.replicate c 0 `LZ.append` s) : hs (c+1)
+
 data HashAlgorithm = MD5 | SHA1 | RIPEMD160 | SHA256 | SHA384 | SHA512 | SHA224 | HashAlgorithm Word8
         deriving (Show, Read, Eq)