diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,30 @@
+Copyright (c) 2013, Li-Ting Tsai
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Li-Ting Tsai nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/Paillier.cabal b/Paillier.cabal
new file mode 100644
--- /dev/null
+++ b/Paillier.cabal
@@ -0,0 +1,39 @@
+
+name:                Paillier
+version:             0.1.0.1
+synopsis:            a simple Paillier cryptosystem    
+description:         a simple Paillier cryptosystem        
+license:             BSD3
+license-file:        LICENSE
+author:              Li-Ting Tsai
+maintainer:          and.liting@gmail.com
+category:            Math
+build-type:          Simple
+cabal-version:       >=1.10
+
+source-repository this
+ type:     git
+ location: https://github.com/onemouth/HsPaillier.git
+ tag: 0.1.0.1
+
+library
+ hs-source-dirs: src
+ exposed-modules: Crypto.Paillier
+ default-language: Haskell2010
+ build-depends: base >=4.6 && <4.7, crypto-numbers >= 0.2.2, crypto-random >= 0.0.7
+
+--executable paillier
+--  main-is: Main.hs            
+--  build-depends:       base >=4.6 && <4.7, cmdargs >= 0.10.5, Paillier >= 0.1.0.0
+--  default-language:    Haskell2010
+
+Test-suite test-Paillier
+  type: exitcode-stdio-1.0
+  hs-source-dirs: src,test
+  main-is: TestMain.hs
+  build-depends: QuickCheck >= 2.6, HUnit, test-framework-th, test-framework, 
+                test-framework-quickcheck2,
+                base >=4.6 && <4.7, crypto-numbers >= 0.2.2, crypto-random >= 0.0.7,
+                Paillier
+  default-language: Haskell2010
+
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/src/Crypto/Paillier.hs b/src/Crypto/Paillier.hs
new file mode 100644
--- /dev/null
+++ b/src/Crypto/Paillier.hs
@@ -0,0 +1,100 @@
+{-# LANGUAGE CPP #-}
+module Crypto.Paillier where
+
+import Data.Maybe
+import Crypto.Random
+import Crypto.Number.Prime
+import Crypto.Number.Generate (generateOfSize, generateBetween)
+import Crypto.Number.ModArithmetic
+
+#if 0
+import System.IO
+#endif
+
+type PlainText = Integer 
+
+type CipherText = Integer
+
+data PubKey = PubKey{  bits :: Int  -- ^ e.g., 2048
+                     , n_modulo :: Integer -- ^ n = pq
+                     , generator :: Integer -- ^ generator = n+1
+                     , n_square :: Integer -- ^ n^2
+                    } deriving (Show)
+
+data PrvKey = PrvKey{  lambda :: Integer -- ^ lambda(n) = lcm(p-1, q-1)
+                     , x :: Integer
+                    } deriving (Show)
+
+
+
+genKey :: Int -> IO (PubKey, PrvKey)
+genKey nBits = do
+    -- | choose random primes
+    pool <- createEntropyPool
+    let rng = cprgCreate pool :: SystemRNG
+    let (p, rng1) = generatePrime rng (nBits `div` 2)
+    let (q, rng2) = generatePrime rng1 (nBits `div` 2)
+    -- | public key parameters
+    let modulo = p*q
+    let g = modulo+1
+    let square = modulo*modulo
+    -- | private key parameters
+    --let phi_n = (p-1)*(q-1)
+    let phi_n = lcm (p-1) (q-1)
+    let maybeU = inverse (((expSafe g phi_n square) - 1) `div` modulo) modulo
+    --let maybeU = inverse phi_n modulo
+    if isNothing maybeU then
+       error "genKey failed." 
+    else
+        return (PubKey{bits=nBits, n_modulo=modulo, generator=g, n_square=square}
+           ,PrvKey{lambda=phi_n, x=(fromJust maybeU)})
+
+-- | deterministic version of encryption
+_encrypt :: PubKey -> PlainText -> Integer -> CipherText
+_encrypt pubKey plaintext r = 
+    result
+    where result = (g_m*r_n) `mod` n_2
+          n_2 = n_square pubKey
+          g_m = expSafe (generator pubKey) plaintext n_2
+          r_n = expSafe r (n_modulo pubKey) n_2
+
+generateR :: SystemRNG -> PubKey -> Integer -> Integer
+generateR rng pubKey guess =
+    if guess >= (n_modulo pubKey) || ((gcd (n_modulo pubKey) guess) > 1) then
+        generateR nextRng pubKey nextGuess
+    else
+        guess
+
+    where (nextGuess, nextRng) = generateBetween rng 1 ((n_modulo pubKey) -1)
+
+encrypt :: PubKey -> PlainText -> IO CipherText
+encrypt pubKey plaintext = do
+    pool <- createEntropyPool
+    let rng = cprgCreate pool :: SystemRNG
+#if 0
+    hSetBuffering stdout NoBuffering
+    putStrLn "get r..."
+#endif
+    let r = generateR rng pubKey (n_modulo pubKey)
+#if 0
+    putStrLn $ "r=" ++ (show r)
+#endif
+    return $ _encrypt pubKey plaintext r 
+
+decrypt :: PrvKey -> PubKey -> CipherText -> PlainText
+decrypt prvKey pubKey ciphertext = 
+    let c_lambda = expSafe ciphertext (lambda prvKey) (n_square pubKey)
+        l_c_lamdba = (c_lambda - 1) `div` (n_modulo pubKey)
+    in  (l_c_lamdba) * (x prvKey) `mod` (n_modulo pubKey)
+
+-- | ciphetext muliplication is known as homomorphic addition of plaintexts
+cipherMul :: PubKey -> CipherText -> CipherText -> CipherText
+cipherMul pubKey c1 c2 = (c1*c2) `mod` (n_square pubKey)
+
+-- | Homomorphic multiplication of plaintexts
+-- An encrypted plaintext raised to the power of another plaintext will decrypt to the product of the two plaintexts.
+cipherExp :: PubKey -> CipherText -> PlainText -> CipherText
+cipherExp pubKey c1 p1 = expSafe c1 p1 (n_square pubKey)
+
+
+
diff --git a/test/TestMain.hs b/test/TestMain.hs
new file mode 100644
--- /dev/null
+++ b/test/TestMain.hs
@@ -0,0 +1,29 @@
+{-# LANGUAGE TemplateHaskell, FlexibleInstances #-}
+
+import Test.QuickCheck
+import Test.QuickCheck.Monadic
+import Test.Framework
+import Test.Framework.TH
+import Test.Framework.Providers.QuickCheck2
+
+import Crypto.Paillier
+
+
+instance Show (IO (PubKey, PrvKey))
+
+instance Arbitrary (IO (PubKey, PrvKey)) where
+    arbitrary = do
+        nBits <- frequency [(2,return 512), (1,return 1024)]
+        return $ genKey nBits
+
+
+prop_fixed_plaintext :: IO (PubKey, PrvKey) -> Property 
+prop_fixed_plaintext keys = monadicIO $ do 
+    (pub, prv) <- run keys
+    let plaintext = 37
+    ciphertext <- run $ encrypt pub plaintext
+    let plaintext' = decrypt prv pub ciphertext
+    assert $ plaintext == plaintext'
+
+main :: IO ()
+main = $(defaultMainGenerator)