1 files changed, 65 insertions, 0 deletions
diff --git a/python/PyECC/ecc/eccrypt.py b/python/PyECC/ecc/eccrypt.py
new file mode 100644
index 000000000..c38876d07
--- /dev/null
+++ b/python/PyECC/ecc/eccrypt.py
@@ -0,0 +1,65 @@
+#   Elliptic Curve Hybrid Encryption Scheme
+#
+#   COPYRIGHT (c) 2010 by Toni Mattis <solaris@live.de>
+#
+
+from curves import get_curve
+from elliptic import mulp
+from encoding import enc_long
+from random import SystemRandom
+from Rabbit import Rabbit
+
+# important for cryptographically secure random numbers:
+random = SystemRandom()
+
+# Encryption Algorithm:
+# ---------------------
+# Input: Message M, public key Q
+#
+# 0. retrieve the group from which Q was generated.
+# 1. generate random number k between 1 and the group order.
+# 2. compute KG = k * G (where G is the base point of the group).
+# 3. compute SG = k * Q (where Q is the public key of the receiver).
+# 4. symmetrically encrypt M to M' using SG's x-coordinate as key.
+#
+# Return: Ciphertext M', temporary key KG
+
+
+def encrypt(message, qk, encrypter = Rabbit):
+    '''Encrypt a message using public key qk => (ciphertext, temp. pubkey)'''
+    bits, q = qk
+    try:
+        bits, cn, n, cp, cq, g = get_curve(bits)
+        if not n:
+            raise ValueError, "Key size %s not suitable for encryption" % bits
+    except KeyError:
+        raise ValueError, "Key size %s not implemented" % bits
+    
+    k = random.randint(1, n - 1)        # temporary private key k
+    kg = mulp(cp, cq, cn, g, k)         # temporary public key k*G
+    sg = mulp(cp, cq, cn, q, k)         # shared secret k*Q = k*d*G
+
+    return encrypter(enc_long(sg[0])).encrypt(message), kg
+
+# Decryption Algorithm:
+# ---------------------
+# Input: Ciphertext M', temporary key KG, private key d
+#
+# 0. retrieve the group from which d and KG were generated.
+# 1. compute SG = q * KG.
+# 2. symmetrically decrypt M' to M using SG's x-coordinate as key.
+#
+# Return: M
+
+def decrypt(message, kg, dk, decrypter = Rabbit):
+    '''Decrypt a message using temp. public key kg and private key dk'''
+    bits, d = dk
+    try:
+        bits, cn, n, cp, cq, g = get_curve(bits)
+    except KeyError:
+        raise ValueError, "Key size %s not implemented" % bits
+
+    sg = mulp(cp, cq, cn, kg, d)        # shared secret d*(k*G) = k*d*G
+    return decrypter(enc_long(sg[0])).decrypt(message)
+    
+