Alice, Bob, and Eve all shared the same "mix and transform" neural network architecture, but they were initialised independently and had no connection other than Alice and Bob's shared key. For Alice the key and plaintext are input into the first layer of the neural network; for Bob the key and the ciphertext were input; and for Eve, she got just the ciphertext. The first layer is fully-connected, so the text and key can mix about. Following the first layer there are a number of convolutional layers, which learn to apply a function to the bits that were handed to it by the previous layer. They don't know what that function might be; they just learn as they go along. For Alice, the final layer spits out some ciphertext; Bob and Eve output what they hope is the plaintext.
Bob and Eve's reconstruction errors during training. You can see that Eve starts to improve, but then a change in the Alice-Bob crypto method shuts her out again.
Enlarge / Bob and Eve's reconstruction errors during training. You can see that Eve starts to improve, but then a change in the Alice-Bob crypto method shuts her out again.
The results were... a mixed bag. Some runs were a complete flop, with Bob never able to reconstruct Alice's messages. Most of the time, Alice and Bob did manage to evolve a system where they could communicate with very few errors. In some tests, Eve showed an improvement over random guessing, but Alice and Bob then usually responded by improving their cryptography technique until Eve had no chance |
