Merge pull request #16 from lc6chang/dev

Add ElGamal.encrypt_point and ElGamal.decrypt_point

README.md

@@ -13,7 +13,7 @@ This is a Python package for ECC and ElGamal elliptic curve encryption.
 
 ## Warning
 
-This project only aims to help you learn and understand what is ECC and how the algorithm works. **Do not use it directly in production environment!**
+This project only aims to help you learn and understand what is ECC and how the algorithm works. **Do not use it directly in the production environment!**
 
 Some cons: The operations of curve points are just implemented in a common way. We don't implement them using [Jacobian Coordinates](https://en.wikibooks.org/wiki/Cryptography/Prime_Curve/Jacobian_Coordinates). Also, we implement them in pure Python. It will be slower than C.
 
@@ -42,14 +42,17 @@ from ecc.cipher import ElGamal
 
 
 # Plaintext
-plain_text = b"This-is-test-plaintext"
+plaintext = b"I am plaintext."
 # Generate key pair
 pri_key, pub_key = gen_keypair(Curve25519)
 # Encrypt using ElGamal algorithm
 cipher_elg = ElGamal(Curve25519)
-C1, C2 = cipher_elg.encrypt(plain_text, pub_key)
+C1, C2 = cipher_elg.encrypt(plaintext, pub_key)
 # Decrypt
 new_plaintext = cipher_elg.decrypt(pri_key, C1, C2)
+
+print(new_plaintext == plaintext)
+# >> True
 ```
 
 ## Common elliptic curve

ecc/cipher.py

@@ -12,11 +12,27 @@ class ElGamal:
 
     def encrypt(self, plaintext: bytes, public_key: Point,
                 randfunc: Callable = None) -> Tuple[Point, Point]:
+        return self.encrypt_bytes(plaintext, public_key, randfunc)
+
+    def decrypt(self, private_key: int, C1: Point, C2: Point) -> bytes:
+        return self.decrypt_bytes(private_key, C1, C2)
+
+    def encrypt_bytes(self, plaintext: bytes, public_key: Point,
+                      randfunc: Callable = None) -> Tuple[Point, Point]:
+        # Encode plaintext into a curve point
+        M = self.curve.encode_point(plaintext)
+        return self.encrypt_point(M, public_key, randfunc)
+
+    def decrypt_bytes(self, private_key: int, C1: Point, C2: Point) -> bytes:
+        M = self.decrypt_point(private_key, C1, C2)
+        return self.curve.decode_point(M)
+
+    def encrypt_point(self, plaintext: Point, public_key: Point,
+                      randfunc: Callable = None) -> Tuple[Point, Point]:
         randfunc = randfunc or urandom
-        # Base point
+        # Base point G
         G = self.curve.G
-        # Encode plaintext into curve point
-        M = self.curve.encode_point(plaintext)
+        M = plaintext
 
         random.seed(randfunc(1024))
         k = random.randint(1, self.curve.n)
@@ -25,6 +41,6 @@ def encrypt(self, plaintext: bytes, public_key: Point,
         C2 = M + k * public_key
         return C1, C2
 
-    def decrypt(self, private_key: int, C1: Point, C2: Point):
+    def decrypt_point(self, private_key: int, C1: Point, C2: Point) -> Point:
         M = C2 + (self.curve.n - private_key) * C1
-        return self.curve.decode_point(M)
+        return M

setup.py

@@ -1,13 +1,14 @@
 from setuptools import setup, find_namespace_packages
+
 from ecc import __version__
 
 dependencies = [
-    "dataclasses"
+    "dataclasses",
 ]
 
 setup(
     name="ecc-pycrypto",
-    author="ChangLiu",
+    author="lc6chang",
     author_email="[email protected]",
     version=__version__,
     packages=find_namespace_packages(),

tests/test_cipher.py

@@ -8,7 +8,7 @@
 
 
 CURVES = [P256, secp256k1, Curve25519, M383, E222, E382]
-PLAIN_TEXT = b"This is a plain text."
+PLAINTEXT = b"I am plaintext."
 
 
 class ElGamalTestCase(unittest.TestCase):
@@ -17,6 +17,18 @@ def test_encrypt_and_decrypt(self):
             with self.subTest(curve=curve):
                 pri_key, pub_key = gen_keypair(curve)
                 cipher_elg = ElGamal(curve)
-                C1, C2 = cipher_elg.encrypt(PLAIN_TEXT, pub_key)
-                plain_text = cipher_elg.decrypt(pri_key, C1, C2)
-                self.assertEqual(plain_text, PLAIN_TEXT)
+                C1, C2 = cipher_elg.encrypt(PLAINTEXT, pub_key)
+                plaintext = cipher_elg.decrypt(pri_key, C1, C2)
+                self.assertEqual(plaintext, PLAINTEXT)
+
+    def test_additive_homomorphism_encryption(self):
+        for curve in CURVES:
+            with self.subTest(curve=curve):
+                pri_key, pub_key = gen_keypair(curve)
+                cipher_elg = ElGamal(curve)
+                plaintext1 = curve.G * 123
+                plaintext2 = curve.G * 456
+                C1, C2 = cipher_elg.encrypt_point(plaintext1, pub_key)
+                C3, C4 = cipher_elg.encrypt_point(plaintext2, pub_key)
+                plaintext = cipher_elg.decrypt_point(pri_key, C1 + C3, C2 + C4)
+                self.assertEqual(plaintext, plaintext1 + plaintext2)