Add a check for salt length in bcrypt function

Raises an error (as the original doc claimed) if the salt is not the
required length of 16 bytes.

validatePasswordEither doesn't require separate checking since the hash
length as a whole is checked, implicitly ensuring the salt is the right
length. Therefore it shouldn't be possible to trigger the error by
calling this function.

Fixes #93.

Crypto/Cipher/Blowfish/Primitive.hs

@@ -79,7 +79,9 @@ initBlowfish key
 -- Cost must be between 4 and 31 inclusive
 -- See <https://www.usenix.org/conference/1999-usenix-annual-technical-conference/future-adaptable-password-scheme>
 eksBlowfish :: (ByteArrayAccess salt, ByteArrayAccess password) => Int -> salt -> password -> Context
-eksBlowfish cost salt key = makeKeySchedule key (Just (salt, cost))
+eksBlowfish cost salt key
+    | B.length salt /= 16 = error "bcrypt salt must be 16 bytes"
+    | otherwise           = makeKeySchedule key (Just (salt, cost))
 
 coreCrypto :: Context -> Word64 -> Word64
 coreCrypto (BF p s0 s1 s2 s3) input = doRound input 0

tests/BCrypt.hs

@@ -74,4 +74,5 @@ makeKATs = concatMap maketest (zip3 is passwords hashes)
 
 tests = testGroup "bcrypt"
     [ testGroup "KATs" makeKATs
+    , testCase "Invalid hash length" (assertEqual "" (Left "Invalid hash format") (validatePasswordEither B.empty ("$2a$06$DCq7YPn5Rq63x1Lad4cll.TV4S6ytwfsfvkgY8jIucDrjc8deX1s" :: B.ByteString)))
     ]