Path: cactus.org!cs.utexas.edu!samsung!olivea!uunet!bonnie.concordia.ca!clyde. + concordia.ca!altitude!elevia!alain From: alain@elevia.UUCP (W.A.Simon) Newsgroups: sci.crypt Subject: eating pretzels Message-ID: <1991Jul2.105754.11804@elevia.UUCP> Date: 2 Jul 91 10:57:54 GMT Followup-To: sci.crypt Organization: The Electronic Path - Global Village Lines: 44 Eating pretzels: I will show that a 2 stream braids is weaker than a simple XOR. If we split a plaintext into two more or less equal parts and braid them together, we have in effect done a transposition. A braid is a particular case of the more general random shuffle. This is a shuffle that has constraints on the valid keys that can be used to randomize the order of the bits. We are working with a reduced key space. Therefore, the two stream braid is weaker than the unconstrained shuffle or transposition. But we know that moving bits around at random is weaker than flipping bits at random (for each shuffle, there is an XOR that can produce it, but the reverse is not true). So we can safely conclude that a two braid stream is weaker than a XOR. This doesn't spell the end of the Braided Streams approach. It just proves that a TWO stream braid is weaker than a XOR. The braiding itself would be of no interest if it were not for the immeasurable strength added by the presence of a totally unpredictable input stream which can't be psyched out through known cryptographical methods (known plaintext attacks would certainly not work here). As a result, we have seen that it is possible to extract any "known" plaintext. This is also reinforced by the possibility of braiding more than two streams at one time, and the benefit of added security at each iteration through the system. These qualities would also be present (to an even greater extent) in the unconstrained Shuffle or XOR of the composite string, but braids lends themselves well to applications that require encryption "as we go", such as live radio or telephone communications, remote sensing and remote control, and any real time usage, where the blocking of data, and the deferred encryption/decryption cycles would introduce unacceptable weakening and delaying elements. In a normal shuffle or a normal XOR, any extra pass through the system would require that the whole message has been processed once, or that arbitrary blocking be performed. With braids, by the simple device of using as many streams as one would like passes through the system, we achieve the required result without batching the messages. To be continue, I am sure. -- William "Alain" Simon alain@elevia.UUCP Frank Zappa for President of the United States of North America!