The PKC Story Continues

advanced_secret_love_message.py

from Crypto.PublicKey import RSA
from Crypto.Hash import SHA256


ross_key = RSA.generate(2048)
ross_pubkey = ross_key.publickey()

# NORMALY THIS MUST BE CREATED ON THE RECIPIENT SIDE!
# Because it involves PRIVATE KEY INFORMATION!
rachel_key = RSA.generate(2048)
# But PUBLIC KEY can be known by everbody
rachel_pubkey = rachel_key.publickey()

# Ross's message
message = "I love you Rachel!"

# First Requirement: Only Rachel can see it
encrypted_message = rachel_pubkey.encrypt(message, '')
print ("\nHow everybody sees the message: " + repr(encrypted_message) + "\n")

decrypted_message = rachel_key.decrypt(encrypted_message)
print ("How Rachel sees the message: " + decrypted_message + "\n")

# Second Requirement: Prove that it is sent from Ross

# Ross will disturb the message
ross_message_hash = SHA256.new(message).hexdigest()
print "Ross's hashed message: ", ross_message_hash

# Then he will sign the message with his private key
ross_signature = ross_key.sign(ross_message_hash, '')

# When Rachel decrypted the message, she will hash it like Ross did
rachel_message_hash = SHA256.new(decrypted_message).hexdigest()
print "Rachel's hashed message: ", rachel_message_hash

# Then she will check the signature with her hashed message
if (ross_pubkey.verify(rachel_message_hash, ross_signature)):
  print "\nHash values match. It is from Ross."
else:
  print "\nHash values not match. It is not from Ross."