lightning-crypto-pytn.py

import Crypto
from Crypto.PublicKey import RSA
from Crypto import Random
from Crypto.Hash import MD5


KEY_LENGTH  = 1024  # Key size (in bits)
#KEY_LENGTH  = 4096  # Key size (in bits)
random_gen = Random.new().read

# Generate RSA private/public key pairs for both parties...
keypair_snowden = RSA.generate(KEY_LENGTH, random_gen)
keypair_pytn    = RSA.generate(KEY_LENGTH, random_gen)

# Public key export for exchange between parties...
pubkey_snowden  = keypair_snowden.publickey()
pubkey_pytn     = keypair_pytn.publickey()

# Plain text messages...
message_to_snowden  = 'You are a patriot!'
message_to_pytn     = "Russia is really nice this time of year...\nUse encryption and make the NSA CPUs churn and burn!"

# Generate digital signatures using private keys...
hash_of_snowden_message = MD5.new(message_to_snowden).digest()
signature_pytn          = keypair_pytn.sign(hash_of_snowden_message, '')
hash_of_pytn_message    = MD5.new(message_to_pytn).digest()
signature_snowden       = keypair_snowden.sign(hash_of_pytn_message, '')

# Encrypt messages using the other party's public key...
encrypted_for_snowden   = pubkey_snowden.encrypt(message_to_snowden, 32)    #from PyTN
encrypted_for_pytn      = pubkey_pytn.encrypt(message_to_pytn, 32)          #from Snowden

# Decrypt messages using own private keys...
decrypted_snowden   = keypair_snowden.decrypt(encrypted_for_snowden)
decrypted_pytn      = keypair_pytn.decrypt(encrypted_for_pytn)

# Signature validation and console output...
hash_snowden_decrypted = MD5.new(decrypted_snowden).digest()
if pubkey_pytn.verify(hash_snowden_decrypted, signature_pytn):
    print "Edward Snowden received from PyTn:"
    print decrypted_snowden
    print ""

hash_pytn_decrypted = MD5.new(decrypted_pytn).digest()
if pubkey_snowden.verify(hash_pytn_decrypted, signature_snowden):
   print "PyTN received from Edward Snowden:"
   print decrypted_pytn