a0a1a2a3a4a5a6a7a8a9 b0b1b2b3b4b5b6b7b8b9 ... z0z1z2z3z4z5z6z7z8z9 If you send the above message repeatedly, changing a single character at a time, in increments (X0a1a2.../aXa1a2...) some interesting things happen to messages encrypted to two keys, especially if they share a one-time pad. These 'interesting things' are wonderful tools for prying open the secrets of a foreign key, using what you already know about the key you are in possession of. If you happen to be working with an encryption program that unwitting allows you to access the one-time pad it is using (or to *supply* the one-time pad it uses), then you can crack secret keys during your lunch breaks and still have time to complete a level of Doom before it is time to get back to work.