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|
{- git-annex crypto
-
- Currently using gpg; could later be modified to support different
- crypto backends if neccessary.
-
- Copyright 2011-2012 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Crypto (
Cipher,
KeyIds(..),
StorableCipher(..),
genEncryptedCipher,
genSharedCipher,
updateEncryptedCipher,
describeCipher,
decryptCipher,
encryptKey,
feedFile,
feedBytes,
readBytes,
encrypt,
decrypt,
Gpg.getGpgEncParams,
prop_HmacSha1WithCipher_sane
) where
import qualified Data.ByteString.Lazy as L
import Data.ByteString.Lazy.UTF8 (fromString)
import Control.Applicative
import Common.Annex
import qualified Utility.Gpg as Gpg
import Types.Key
import Types.Crypto
{- The beginning of a Cipher is used for MAC'ing; the remainder is used
- as the GPG symmetric encryption passphrase when using the hybrid
- scheme. Note that the cipher itself is base-64 encoded, hence the
- string is longer than 'cipherSize': 683 characters, padded to 684.
-
- The 256 first characters that feed the MAC represent at best 192
- bytes of entropy. However that's more than enough for both the
- default MAC algorithm, namely HMAC-SHA1, and the "strongest"
- currently supported, namely HMAC-SHA512, which respectively need
- (ideally) 64 and 128 bytes of entropy.
-
- The remaining characters (320 bytes of entropy) is enough for GnuPG's
- symetric cipher; unlike weaker public key crypto, the key does not
- need to be too large.
-}
cipherBeginning :: Int
cipherBeginning = 256
cipherSize :: Int
cipherSize = 512
cipherPassphrase :: Cipher -> String
cipherPassphrase (Cipher c) = drop cipherBeginning c
cipherMac :: Cipher -> String
cipherMac (Cipher c) = take cipherBeginning c
{- Creates a new Cipher, encrypted to the specified key id. -}
genEncryptedCipher :: String -> EncryptedCipherVariant -> Bool -> IO StorableCipher
genEncryptedCipher keyid variant highQuality = do
ks <- Gpg.findPubKeys keyid
random <- Gpg.genRandom highQuality size
encryptCipher (Cipher random) variant ks
where
size = case variant of
HybridCipher -> cipherSize -- used for MAC + symmetric
PubKeyCipher -> cipherBeginning -- only used for MAC
{- Creates a new, shared Cipher. -}
genSharedCipher :: Bool -> IO StorableCipher
genSharedCipher highQuality =
SharedCipher <$> Gpg.genRandom highQuality cipherSize
{- Updates an existing Cipher, re-encrypting it to add or remove keyids,
- depending on whether the first component is True or False. -}
updateEncryptedCipher :: [(Bool, String)] -> StorableCipher -> IO StorableCipher
updateEncryptedCipher _ SharedCipher{} = undefined
updateEncryptedCipher [] encipher = return encipher
updateEncryptedCipher newkeys encipher@(EncryptedCipher _ symmetric (KeyIds ks)) = do
dropKeys <- listKeyIds [ k | (False, k) <- newkeys ]
forM_ dropKeys $ \k -> unless (k `elem` ks) $
error $ "Key " ++ k ++ " was not present; cannot remove."
addKeys <- listKeyIds [ k | (True, k) <- newkeys ]
let ks' = (addKeys ++ ks) \\ dropKeys
when (null ks') $
error "Cannot remove the last key."
cipher <- decryptCipher encipher
encryptCipher cipher symmetric $ KeyIds ks'
where
listKeyIds = mapM (Gpg.findPubKeys >=*> keyIds) >=*> concat
describeCipher :: StorableCipher -> String
describeCipher (SharedCipher _) = "shared cipher"
describeCipher (EncryptedCipher _ variant (KeyIds ks)) =
scheme ++ " with gpg " ++ keys ks ++ " " ++ unwords ks
where
scheme = case variant of
HybridCipher -> "hybrid cipher"
PubKeyCipher -> "pubkey crypto"
keys [_] = "key"
keys _ = "keys"
{- Encrypts a Cipher to the specified KeyIds. -}
encryptCipher :: Cipher -> EncryptedCipherVariant -> KeyIds -> IO StorableCipher
encryptCipher (Cipher c) variant (KeyIds ks) = do
-- gpg complains about duplicate recipient keyids
let ks' = nub $ sort ks
-- The cipher itself is always encrypted to the given public keys
let params = Gpg.pkEncTo ks' ++ Gpg.stdEncryptionParams False
encipher <- Gpg.pipeStrict params c
return $ EncryptedCipher encipher variant (KeyIds ks')
{- Decrypting an EncryptedCipher is expensive; the Cipher should be cached. -}
decryptCipher :: StorableCipher -> IO Cipher
decryptCipher (SharedCipher t) = return $ Cipher t
decryptCipher (EncryptedCipher t _ _) =
Cipher <$> Gpg.pipeStrict [ Param "--decrypt" ] t
{- Generates an encrypted form of a Key. The encryption does not need to be
- reversable, nor does it need to be the same type of encryption used
- on content. It does need to be repeatable. -}
encryptKey :: Mac -> Cipher -> Key -> Key
encryptKey mac c k = Key
{ keyName = macWithCipher mac c (key2file k)
, keyBackendName = "GPG" ++ showMac mac
, keySize = Nothing -- size and mtime omitted
, keyMtime = Nothing -- to avoid leaking data
}
type Feeder = Handle -> IO ()
type Reader a = Handle -> IO a
feedFile :: FilePath -> Feeder
feedFile f h = L.hPut h =<< L.readFile f
feedBytes :: L.ByteString -> Feeder
feedBytes = flip L.hPut
readBytes :: (L.ByteString -> IO a) -> Reader a
readBytes a h = L.hGetContents h >>= a
{- Runs a Feeder action, that generates content that is symmetrically
- encrypted with the Cipher (unless it is empty, in which case
- public-key encryption is used) using the given gpg options, and then
- read by the Reader action. Note: For public-key encryption,
- recipients MUST be included in 'params' (for instance using
- 'getGpgEncParams'). -}
encrypt :: [CommandParam] -> Cipher -> Feeder -> Reader a -> IO a
encrypt params cipher = Gpg.feedRead params' pass
where
pass = cipherPassphrase cipher
params' = params ++ Gpg.stdEncryptionParams (not $ null pass)
{- Runs a Feeder action, that generates content that is decrypted with the
- Cipher (or using a private key if the Cipher is empty), and read by the
- Reader action. -}
decrypt :: Cipher -> Feeder -> Reader a -> IO a
decrypt = Gpg.feedRead [Param "--decrypt"] . cipherPassphrase
macWithCipher :: Mac -> Cipher -> String -> String
macWithCipher mac c = macWithCipher' mac (cipherMac c)
macWithCipher' :: Mac -> String -> String -> String
macWithCipher' mac c s = calcMac mac (fromString c) (fromString s)
{- Ensure that macWithCipher' returns the same thing forevermore. -}
prop_HmacSha1WithCipher_sane :: Bool
prop_HmacSha1WithCipher_sane = known_good == macWithCipher' HmacSha1 "foo" "bar"
where
known_good = "46b4ec586117154dacd49d664e5d63fdc88efb51"
|
