-- |
-- Module      : Crypto.PubKey.Rabin.Modified
-- License     : BSD-style
-- Maintainer  : Carlos Rodriguez-Vega <crodveg@yahoo.es>
-- Stability   : experimental
-- Portability : unknown
--
-- Modified-Rabin public-key digital signature algorithm.
-- See algorithm 11.30 in "Handbook of Applied Cryptography" by Alfred J. Menezes et al.
--
{-# LANGUAGE DeriveDataTypeable #-}
module Crypto.PubKey.Rabin.Modified
    ( PublicKey(..)
    , PrivateKey(..)
    , generate
    , sign
    , verify
    ) where

import           Data.ByteString
import           Data.Data

import           Crypto.Hash
import           Crypto.Number.ModArithmetic (expSafe, jacobi)
import           Crypto.Number.Serialize (os2ip)
import           Crypto.PubKey.Rabin.Types
import           Crypto.Random.Types

-- | Represent a Modified-Rabin public key.
data PublicKey = PublicKey
    { PublicKey -> Int
public_size :: Int      -- ^ size of key in bytes
    , PublicKey -> Integer
public_n    :: Integer  -- ^ public p*q
    } deriving (Int -> PublicKey -> ShowS
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-- | Represent a Modified-Rabin private key.
data PrivateKey = PrivateKey
    { PrivateKey -> PublicKey
private_pub :: PublicKey
    , PrivateKey -> Integer
private_p   :: Integer   -- ^ p prime number
    , PrivateKey -> Integer
private_q   :: Integer   -- ^ q prime number
    , PrivateKey -> Integer
private_d   :: Integer
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-- | Generate a pair of (private, public) key of size in bytes.
-- Prime p is congruent 3 mod 8 and prime q is congruent 7 mod 8.
generate :: MonadRandom m
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publicKey, PrivateKey
privateKey)

-- | Sign message using hash algorithm and private key.
sign :: HashAlgorithm hash
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     -> ByteString    -- ^ message to sign
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sign :: PrivateKey -> hash -> ByteString -> Either Error Integer
sign PrivateKey
pk hash
hashAlg ByteString
m =
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d = PrivateKey -> Integer
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pk
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public_n (PublicKey -> Integer) -> PublicKey -> Integer
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pk
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h Integer -> Integer -> Integer
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+ Integer
6
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InvalidParameters

-- | Verify signature using hash algorithm and public key.
verify :: HashAlgorithm hash
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       -> hash          -- ^ hash function
       -> ByteString    -- ^ message
       -> Integer       -- ^ signature
       -> Bool
verify :: PublicKey -> hash -> ByteString -> PrimeCondition
verify PublicKey
pk hash
hashAlg ByteString
m Integer
s =
    let n :: Integer
n   = PublicKey -> Integer
public_n PublicKey
pk
        h :: Integer
h   = Digest hash -> Integer
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os2ip (Digest hash -> Integer) -> Digest hash -> Integer
forall a b. (a -> b) -> a -> b
$ hash -> ByteString -> Digest hash
forall ba alg.
(ByteArrayAccess ba, HashAlgorithm alg) =>
alg -> ba -> Digest alg
hashWith hash
hashAlg ByteString
m
        s' :: Integer
s'  = Integer -> Integer -> Integer -> Integer
expSafe Integer
s Integer
2 Integer
n
        s'' :: Integer
s'' = case Integer
s' Integer -> Integer -> Integer
forall a. Integral a => a -> a -> a
`mod` Integer
8 of
            Integer
6 -> Integer
s'
            Integer
3 -> Integer
2Integer -> Integer -> Integer
forall a. Num a => a -> a -> a
*Integer
s'
            Integer
7 -> Integer
n Integer -> Integer -> Integer
forall a. Num a => a -> a -> a
- Integer
s'
            Integer
2 -> Integer
2Integer -> Integer -> Integer
forall a. Num a => a -> a -> a
*(Integer
n Integer -> Integer -> Integer
forall a. Num a => a -> a -> a
- Integer
s')
            Integer
_ -> Integer
0
     in case Integer
s'' Integer -> Integer -> Integer
forall a. Integral a => a -> a -> a
`mod` Integer
16 of
            Integer
6 -> let h' :: Integer
h' = (Integer
s'' Integer -> Integer -> Integer
forall a. Num a => a -> a -> a
- Integer
6) Integer -> Integer -> Integer
forall a. Integral a => a -> a -> a
`div` Integer
16
                  in Integer
h' Integer -> PrimeCondition
forall a. Eq a => a -> a -> Bool
== Integer
h 
            Integer
_ -> Bool
False