Re: Re[2]: [Haskell-cafe] Password hashing

Sorry about the hideous formatting above. Reattached as a text file. t. 2008/11/26 Thomas Hartman :

OK, I went ahead and implemented pbkdf2, following the algorithm linked to by bulat and Michael.

If there are any crypto gurus who can code-review this I would be much obliged, and when I'm confident enough that this does the right thing I'll put it up on hackage.

I don't do much crypto so this *definitely* needs a review before it becomes a library?

How's this looks, cafe?

Thanks!

Thomas.

{-# LANGUAGE ScopedTypeVariables #-} module Crypto.PBKDF2 (pbkdf2, pbkdf2') where

import qualified Data.ByteString.Char8 as B import qualified Data.ByteString.Lazy as L import GHC.Word import Control.Monad (foldM) import Random import Data.Digest.SHA512 (hash) import Data.Word import Data.Bits import Data.Binary

newtype Password = Password [Word8] newtype Salt = Salt [Word8] newtype HashedPass = HashedPass [Word8] deriving Show {- | A reasonable default for rsa pbkdf2? Actually I'm not really sure, ask folk with more experience.

...

pbkdf2 = pbkdf2' prfSHA512 512 512 512 -} t = pbkdf2 ( Password . toWord8s $ "meh" ) ( Salt . toWord8s $ "moo" ) pbkdf2 :: Password -> Salt -> HashedPass pbkdf2 = pbkdf2' prfSHA512 512 512 512

{- | Password Based Key Derivation Function, from RSA labs.

...

pbkdf2' prf hlen cIters dklen (Password pass) (Salt salt) -} pbkdf2' :: ([Word8] -> [Word8] -> [Word8]) -> Integer -> Integer -> Integer -> Password -> Salt -> HashedPass pbkdf2' prf hlen cIters dklen (Password pass) (Salt salt) | dklen > ( (2^32-1) * hlen) = error $ "pbkdf2, (dklen,hlen) : " ++ (show (dklen,hlen)) | otherwise = let --l,r :: Int l = ceiling $ (fromIntegral dklen) / (fromIntegral hlen ) r = dklen - ( (l-1) * hlen) ustream :: [Word8] -> [Word8] -> [[Word8]] ustream p s = let x = prf p s in x : ustream p x --us :: Integer -> [[Word8]] us i = take (fromIntegral cIters) $ ustream pass ( salt `myor` ((intToFourWord8s i) )) --f :: [Word8] -> [Word8] -> Integer -> Integer -> [Word8] f pass salt cIters i = foldr1 myxor $ us i ts :: [[Word8]] ts = map (f pass salt cIters) ( [1..l] ) in HashedPass . take (fromIntegral dklen) . concat $ ts

-- The spec says -- Here, INT (i) is a four-octet encoding of the integer i, most significant octet first. -- I'm reading from the right... is this the right thing? toWord8s x = L.unpack . encode $ x

--intToFourWord8s :: Integer -> [Word8] intToFourWord8s i = let w8s = toWord8s $ i in drop (length w8s -4) w8s

myxor :: [Word8] -> [Word8] -> [Word8] myxor = zipWith xor

myor :: [Word8] -> [Word8] -> [Word8] myor = zipWith (.|.)

prfSHA512 :: [Word8] -> [Word8] -> [Word8] prfSHA512 x y = hash $ x ++ y

2008/11/26 John Meacham :

...

What you are using there is not a salt, but rather a secret key. The important thing about a salt is that it is different for _every user_. and you actually store the salt unhashed along with the hash. (it is not secret information). A salt protects against a dictionary attack, for instance, you might have a dictionary of hash's and the common passwords they go to but if you add a 32 bit salt, you would need 2^32 entries for each dictionary word, making such an attack unworkable. You can also trivially tell if two users have the _same_ password just by comparing the hashes without a salt.

John

-- John Meacham - ⑆repetae.net⑆john⑈ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe