An occasionally useful toy.

[PBrennick]

Hutch,
That is correct and is the reason I use pattern overlays, just another term for what you are talking about.  One of the things XOR encoding is useful for and was necessary in some of my jobs was after the data was unencrypted by the master cypher it was now in a position to be decoded after having been encoded by several people.  In other words, each person would encode the data using their own private key (similar to logging in) and then the master encryption is performed.  Using this method, it required several people to unlock the data (this was something THEY required).  The point is, using the XOR encoding/decoding method, the result is not 'order dependant' which means the data could be encoded by users in the sequence of A,B,C,D but the decoding did not need to be D,C,B,A and could, in fact be in any order.  This was VERY important because people are people and an order driven encoding using any other method would yield incomprehensible garbage if the decoding order was not rigidly followed.  After losing one database, I decided to find a way that prevented this possible loss and XOR pattern encoding/decoding was the answer and in an environment where there are multiple encodings (these are pattern overlays) is going on, it is not easily broken.  It was always broken using Cray computers with a lot of processing overhead but passed a certain level of difficulty that was established by the client.

People can say all they want about this is easily broken but as I said before in this thread, how about I encode a file and they decode it?  I bet I don't get any takers.

Paul

[Tedd]

M xor A xor B xor C xor D = M xor K

(where K is a single key = A xor B xor C xor D)


In other words, you only need to figure out one suitable key to be able to decrypt, not four.



And finding the key for encrypted plain english text is not as difficult as it might seem, as long as the key is some length shorter than the message ie. allows for a few repeats; without any repeats it's equivalent to a one-time pad, which is theoretically unbreakable.