I've got a probability problem that outstrips my knowledge so I'd be grateful for any help. I've looked online for an answer and also on maths sites but it didn't help. The answer would also help others in the same situation. The issue is :-
I am using a one time pad to encrypt some text. This is perfect encryption unless someone knows part of the text or at least the subject of the text as it can then be run through statistical analysis for known words. What I was trying to work out was the probability of working out the rest of the text from known words in the text. Say I have a text message that reads 'Meet me at 9pm to discuss the new car engine designed by Rod and Sarah'. The characters are encrypted via XOR with a random number 1-255 and this key is never re-used. The decryption people know that the message contains 'Rob', 'engine' and 'Meet'. What is the probability or chance (if such a thing exists) of the rest of the text being decrypted? I'd be most grateful too for any explanations of the working so I can apply it in the future.