Added SKEIN256 and SKEIN512 backends

SHA3 is still waiting for final standardization.
Although this is looking less likely given
https://www.cdt.org/blogs/joseph-lorenzo-hall/2409-nist-sha-3

In the meantime, cryptohash implements skein, and it's used by some of the
haskell ecosystem (for yesod sessions, IIRC), so this implementation is
likely to continue working. Also, I've talked with the cryprohash author
and he's a reasonable guy.

It makes sense to have an alternate high security hash, in case some
horrible attack is found against SHA2 tomorrow, or in case SHA3 comes out
and worst fears are realized.

I'd also like to support using skein for HMAC. But no hurry there and
a new version of cryptohash has much nicer HMAC code, so I will probably
wait until I can use that version.

1 files changed, 0 insertions, 148 deletions

diff --git a/Backend/SHA.hs b/Backend/SHA.hs
deleted file mode 100644
index 42cde3f57..000000000
--- a/Backend/SHA.hs
+++ /dev/null
@@ -1,148 +0,0 @@
-{- git-annex SHA backends
- -
- - Copyright 2011-2013 Joey Hess <joey@kitenet.net>
- -
- - Licensed under the GNU GPL version 3 or higher.
- -}
-
-module Backend.SHA (backends) where
-
-import Common.Annex
-import qualified Annex
-import Types.Backend
-import Types.Key
-import Types.KeySource
-import Utility.Hash
-import Utility.ExternalSHA
-
-import qualified Build.SysConfig as SysConfig
-import qualified Data.ByteString.Lazy as L
-import Data.Char
-
-type SHASize = Int
-
-{- Order is slightly significant; want SHA256 first, and more general
- - sizes earlier. -}
-sizes :: [Int]
-sizes = [256, 1, 512, 224, 384]
-
-{- The SHA256E backend is the default. -}
-backends :: [Backend]
-backends = catMaybes $ map genBackendE sizes ++ map genBackend sizes
-
-genBackend :: SHASize -> Maybe Backend
-genBackend size = Just Backend
-	{ name = shaName size
-	, getKey = keyValue size
-	, fsckKey = Just $ checkKeyChecksum size
-	, canUpgradeKey = Just needsUpgrade
-	}
-
-genBackendE :: SHASize -> Maybe Backend
-genBackendE size = do
-	b <- genBackend size
-	return $ b 
-		{ name = shaNameE size
-		, getKey = keyValueE size
-		}
-
-shaName :: SHASize -> String
-shaName size = "SHA" ++ show size
-
-shaNameE :: SHASize -> String
-shaNameE size = shaName size ++ "E"
-
-shaN :: SHASize -> FilePath -> Integer -> Annex String
-shaN shasize file filesize = do
-	showAction "checksum"
-	liftIO $ case shaCommand shasize filesize of
-		Left sha -> sha <$> L.readFile file
-		Right command ->
-			either error return 
-				=<< externalSHA command shasize file
-
-shaCommand :: SHASize -> Integer -> Either (L.ByteString -> String) String
-shaCommand shasize filesize
-	| shasize == 1 = use SysConfig.sha1 sha1
-	| shasize == 256 = use SysConfig.sha256 sha256
-	| shasize == 224 = use SysConfig.sha224 sha224
-	| shasize == 384 = use SysConfig.sha384 sha384
-	| shasize == 512 = use SysConfig.sha512 sha512
-	| otherwise = error $ "bad sha size " ++ show shasize
-  where
-	use Nothing hasher = Left $ show . hasher
-	use (Just c) hasher
-		{- Use builtin, but slightly slower hashing for
-		 - smallish files. Cryptohash benchmarks 90 to 101%
-		 - faster than external hashers, depending on the hash
-		 - and system. So there is no point forking an external
-		 - process unless the file is large. -}
-		| filesize < 1048576 = use Nothing hasher
-		| otherwise = Right c
-
-{- A key is a checksum of its contents. -}
-keyValue :: SHASize -> KeySource -> Annex (Maybe Key)
-keyValue shasize source = do
-	let file = contentLocation source
-	stat <- liftIO $ getFileStatus file
-	let filesize = fromIntegral $ fileSize stat
-	s <- shaN shasize file filesize
-	return $ Just $ stubKey
-		{ keyName = s
-		, keyBackendName = shaName shasize
-		, keySize = Just filesize
-		}
-
-{- Extension preserving keys. -}
-keyValueE :: SHASize -> KeySource -> Annex (Maybe Key)
-keyValueE size source = keyValue size source >>= maybe (return Nothing) addE
-  where
-	addE k = return $ Just $ k
-		{ keyName = keyName k ++ selectExtension (keyFilename source)
-		, keyBackendName = shaNameE size
-		}
-
-selectExtension :: FilePath -> String
-selectExtension f
-	| null es = ""
-	| otherwise = intercalate "." ("":es)
-  where
-	es = filter (not . null) $ reverse $
-		take 2 $ takeWhile shortenough $
-		reverse $ split "." $ filter validExtension $ takeExtensions f
-	shortenough e = length e <= 4 -- long enough for "jpeg"
-
-{- A key's checksum is checked during fsck. -}
-checkKeyChecksum :: SHASize -> Key -> FilePath -> Annex Bool
-checkKeyChecksum size key file = do
-	fast <- Annex.getState Annex.fast
-	mstat <- liftIO $ catchMaybeIO $ getFileStatus file
-	case (mstat, fast) of
-		(Just stat, False) -> do
-			let filesize = fromIntegral $ fileSize stat
-			check <$> shaN size file filesize
-		_ -> return True
-  where
-	sha = keySha key
-	check s
-		| s == sha = True
-		{- A bug caused checksums to be prefixed with \ in some
-		 - cases; still accept these as legal now that the bug has been
-		 - fixed. -}
-		| '\\' : s == sha = True
-		| otherwise = False
-
-keySha :: Key -> String
-keySha key = dropExtensions (keyName key)
-
-validExtension :: Char -> Bool
-validExtension c
-	| isAlphaNum c = True
-	| c == '.' = True
-	| otherwise = False
-
-{- Upgrade keys that have the \ prefix on their sha due to a bug, or
- - that contain non-alphanumeric characters in their extension. -}
-needsUpgrade :: Key -> Bool
-needsUpgrade key = "\\" `isPrefixOf` keySha key ||
-	any (not . validExtension) (takeExtensions $ keyName key)