def elgamal_encrypt(recipient_pubkey, msg, msg_width_bits):
k = ECPrivateKey.generate(curve)
C1 = k.pubkey.point
C2 = k.scalar * recipient_pubkey.point
P_m = msg_to_point(curve, msg, msg_width_bits=msg_width_bits)
ciphertext = (C1, C2 + P_m)
return ciphertext
k = ECPrivateKey.generate(curve)
C1 = k.pubkey.point
C2 = k.scalar * recipient_pubkey.point
P_m = msg_to_point(curve, msg, msg_width_bits=msg_width_bits)
ciphertext = (C1, C2 + P_m)
return ciphertext
def elgamal_decrypt(recipient_privkey, ciphertext, msg_width_bits):
(C1, C2) = ciphertext
Cp = C1 * recipient_privkey.scalar
P_m = C2 + (-Cp)
int_message = int(P_m.x) & ((1 << msg_width_bits) - 1)
msg = int.to_bytes(int_message,
byteorder="little",
length=(msg_width_bits + 7) // 8)
return msg
privkey = ECPrivateKey.generate(curve)
pubkey = privkey.pubkey
message = b"foobar"
print("Message:", message)
ciphertext = elgamal_encrypt(pubkey, message, msg_width_bits=256)
print("Ciphertext:")
print(" C1 =", ciphertext[0])
print(" C2 =", ciphertext[1])
plaintext = elgamal_decrypt(privkey, ciphertext, msg_width_bits=256)
print("Plaintext:", plaintext)
