Quote:
Originally Posted by xander biscuits
All the computer stuff is beyond me but there are some on this forum who would be able to do this I'm sure. I'd just Caesar Cipher it send it to Alice and then she'd Caesar Cipher it again and then I'd undo mine and she'd undo hers and read.
But something more complicated than a Caesar Cipher
Actually it's a good start, you just described the three pass protocol, using commutative encryption where encryption/decryption doesnt matter.
Bob encrypts/sends message to Alice, Alice encrypts again and sends to Bob, then bob decrypts and sens back to Alice who decrypts and reads the message. and you just sent the encrypted message without sharing keys!
Ceaser Cipher is fine for this, but you can add more security to make code breaking tougher. ie exploiting at character frequency of looking for letter combinations such as ". " or "qu".
Also, your vulnerable to man in the middle attacks which is like the Mission Impossible movie, forget which, where IMF agents played both the buyer and seller of nuke codes against both villains.
eg hacker intercepts message from Bob, encrypts and sends it back to Bob pretending to be Alice. Once he gets the message, he pretends to be Bob and sends it to Alice, and neither are the wiser.