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authorMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
committerMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
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+# 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)
+
+