A plaintext injection attack against the 8 bit "stupid" cipher.
The xor operation has a magical property - it preserves randomness. If you take a known value and xor it with a random value, the result is another random value.
This is the basis of many stream ciphers; a stream of independent, uniformly distributed, random values is xored against the plaintext. If the original random stream if "really" random, then the plaintext will be too.
This gives the xor operation has a certain attractiveness - it seems like the perfect building blog for constructing other cryptographic functions.
Say you wanted to make your own stream cipher. We've just seen how to build one from a source of random numbers, but how do you construct those numbers? Xor seems like an obvious choice - start with some intiial values (the key, perhaps) and xor them together.
TODO