diff --git a/Crypto/Cipher/Tests/KATs.hs b/Crypto/Cipher/Tests/KATs.hs
--- a/Crypto/Cipher/Tests/KATs.hs
+++ b/Crypto/Cipher/Tests/KATs.hs
@@ -11,34 +11,34 @@
 
 -- | ECB KAT
 data KAT_ECB = KAT_ECB
-    { ecbKey        :: ByteString
-    , ecbPlaintext  :: ByteString
-    , ecbCiphertext :: ByteString
+    { ecbKey        :: ByteString -- ^ Key
+    , ecbPlaintext  :: ByteString -- ^ Plaintext
+    , ecbCiphertext :: ByteString -- ^ Ciphertext
     } deriving (Show,Eq)
 
 -- | CBC KAT
 data KAT_CBC = KAT_CBC
-    { cbcKey        :: ByteString
-    , cbcIV         :: ByteString
-    , cbcPlaintext  :: ByteString
-    , cbcCiphertext :: ByteString
+    { cbcKey        :: ByteString -- ^ Key
+    , cbcIV         :: ByteString -- ^ IV
+    , cbcPlaintext  :: ByteString -- ^ Plaintext
+    , cbcCiphertext :: ByteString -- ^ Ciphertext
     } deriving (Show,Eq)
 
 -- | CTR KAT
 data KAT_CTR = KAT_CTR
-    { ctrKey        :: ByteString
-    , ctrIV         :: ByteString
-    , ctrPlaintext  :: ByteString
-    , ctrCiphertext :: ByteString
+    { ctrKey        :: ByteString -- ^ Key
+    , ctrIV         :: ByteString -- ^ IV (usually represented as a 128 bits integer)
+    , ctrPlaintext  :: ByteString -- ^ Plaintext 
+    , ctrCiphertext :: ByteString -- ^ Ciphertext
     } deriving (Show,Eq)
 
 -- | XTS KAT
 data KAT_XTS = KAT_XTS
-    { xtsKey1       :: ByteString
-    , xtsKey2       :: ByteString
-    , xtsIV         :: ByteString
-    , xtsPlaintext  :: ByteString
-    , xtsCiphertext :: ByteString
+    { xtsKey1       :: ByteString -- ^ 1st XTS key
+    , xtsKey2       :: ByteString -- ^ 2nd XTS key
+    , xtsIV         :: ByteString -- ^ XTS IV
+    , xtsPlaintext  :: ByteString -- ^ plaintext
+    , xtsCiphertext :: ByteString -- ^ Ciphertext
     } deriving (Show,Eq)
 
 -- | AEAD KAT
@@ -53,6 +53,8 @@
     , aeadTag        :: AuthTag    -- ^ expected tag
     } deriving (Show,Eq)
 
+-- | all the KATs. use defaultKATs to prevent compilation error
+-- from future expansion of this data structure
 data KATs = KATs
     { kat_ECB  :: [KAT_ECB]
     , kat_CBC  :: [KAT_CBC]
@@ -61,6 +63,7 @@
     , kat_AEAD :: [KAT_AEAD]
     } deriving (Show,Eq)
 
+-- | the empty KATs
 defaultKATs :: KATs
 defaultKATs = KATs
     { kat_ECB  = []
@@ -70,6 +73,7 @@
     , kat_AEAD = []
     }
 
+-- | tests related to KATs
 testKATs :: BlockCipher cipher => KATs -> cipher -> Test
 testKATs kats cipher = testGroup "KAT"
     (   maybeGroup makeECBTest "ECB" (kat_ECB kats)
@@ -124,7 +128,9 @@
         nbs = [0..]
         
         cipherMakeKey :: BlockCipher cipher => cipher -> ByteString -> Key cipher
-        cipherMakeKey _ bs = fromJust $ makeKey bs
+        cipherMakeKey c bs = case makeKey bs of
+                                Left e -> error ("invalid key " ++ show bs ++ " for " ++ show (cipherName c) ++ " " ++ show e)
+                                Right k  -> k
 
         cipherMakeIV :: BlockCipher cipher => cipher -> ByteString -> IV cipher
         cipherMakeIV _ bs = fromJust $ makeIV bs
diff --git a/Crypto/Cipher/Tests/Properties.hs b/Crypto/Cipher/Tests/Properties.hs
--- a/Crypto/Cipher/Tests/Properties.hs
+++ b/Crypto/Cipher/Tests/Properties.hs
@@ -45,21 +45,29 @@
 instance Show (AEADUnit a) where
     show (AEADUnit key iv aad b) = "AEAD(key=" ++ show (toBytes key) ++ ",iv=" ++ show iv ++ ",aad=" ++ show (toBytes aad) ++ ",input=" ++ show b ++ ")"
 
+-- | Generate an arbitrary valid key for a specific block cipher
 generateKey :: BlockCipher a => Gen (Key a)
 generateKey = keyFromCipher undefined
   where keyFromCipher :: BlockCipher a => a -> Gen (Key a)
-        keyFromCipher cipher = case cipherKeySize cipher of
-                                Just sz -> fromJust . makeKey . B.pack <$> replicateM sz arbitrary
-                                Nothing -> fromJust . makeKey . B.pack <$> (choose (1,66) >>= \sz -> replicateM sz arbitrary)
+        keyFromCipher cipher = do
+            sz <- case cipherKeySize cipher of
+                         KeySizeRange low high -> choose (low, high)
+                         KeySizeFixed v -> return v
+                         KeySizeEnum l  -> elements l
+            either (error . show) id . makeKey . B.pack <$> replicateM sz arbitrary
 
+-- | Generate an arbitrary valid IV for a specific block cipher
 generateIv :: BlockCipher a => Gen (IV a)
 generateIv = ivFromCipher undefined
   where ivFromCipher :: BlockCipher a => a -> Gen (IV a)
         ivFromCipher cipher = fromJust . makeIV . B.pack <$> replicateM (blockSize cipher) arbitrary
 
+-- | Generate an arbitrary valid IV for AEAD for a specific block cipher
 generateIvAEAD :: Gen B.ByteString
 generateIvAEAD = choose (12,90) >>= \sz -> (B.pack <$> replicateM sz arbitrary)
 
+-- | Generate a plaintext multiple of 16 bytes. TODO replace by one function that use the blockSize
+-- cipher instance
 generatePlaintextMultiple16 :: Gen B.ByteString
 generatePlaintextMultiple16 = choose (1,128) >>= \size -> replicateM (size*16) arbitrary >>= return . B.pack
 
@@ -92,6 +100,8 @@
                          <*> generatePlaintext
                          <*> generatePlaintext
 
+-- | Test a generic block cipher for properties
+-- related to block cipher modes.
 testModes :: BlockCipher a => a -> [Test]
 testModes cipher =
     [ testGroup "decrypt.encrypt==id"
@@ -125,8 +135,9 @@
         testProperty_CTR (CTRUnit (cipherInit -> ctx) testIV plaintext) =
             plaintext `assertEq` ctrCombine ctx testIV (ctrCombine ctx testIV plaintext)
 
-        testProperty_XTS (XTSUnit (cipherInit -> ctx1) (cipherInit -> ctx2) testIV plaintext) =
-            plaintext `assertEq` xtsDecrypt (ctx1, ctx2) testIV 0 (xtsEncrypt (ctx1, ctx2) testIV 0 plaintext)
+        testProperty_XTS (XTSUnit (cipherInit -> ctx1) (cipherInit -> ctx2) testIV plaintext)
+            | blockSize ctx1 == 16 = plaintext `assertEq` xtsDecrypt (ctx1, ctx2) testIV 0 (xtsEncrypt (ctx1, ctx2) testIV 0 plaintext)
+            | otherwise            = True
 
         testProperty_AEAD mode (AEADUnit (cipherInit -> ctx) testIV aad plaintext) =
             case aeadInit mode ctx testIV of
diff --git a/crypto-cipher-tests.cabal b/crypto-cipher-tests.cabal
--- a/crypto-cipher-tests.cabal
+++ b/crypto-cipher-tests.cabal
@@ -1,5 +1,5 @@
 Name:                crypto-cipher-tests
-Version:             0.0.2
+Version:             0.0.3
 Synopsis:            Generic cryptography cipher tests
 Description:         Generic cryptography cipher tests
 License:             BSD3
@@ -27,7 +27,7 @@
                    , bytestring
                    , byteable >= 0.1.1
                    , securemem >= 0.1.1
-                   , crypto-cipher-types
+                   , crypto-cipher-types >= 0.0.3
   ghc-options:       -Wall -fwarn-tabs
 
 Test-Suite test-crypto-cipher-dummy
@@ -37,7 +37,7 @@
   Build-Depends:     base >= 3 && < 5
                    , bytestring
                    , byteable
-                   , crypto-cipher-types
+                   , crypto-cipher-types >= 0.0.3
                    , crypto-cipher-tests
                    , mtl
                    , QuickCheck >= 2