When XOR – is your friend…

Using a random enough input stream may sound like outright blasphemy to many if not all reading this; however in this article I will demonstrate when using it makes sense.
Author: ISRAEL TORRES
Source: Hakin9 10/2010 http://hakin9.org

What you will learn…

• Using a PRNG with XOR to create and analyze a self-keying cipher

What you should know…

• Basic cryptographic knowledge, bash, C

One of my hobbies includes creating crypto challenges where I hide an English message string in a block of numbers and letters. The first challenger that can correctly find what the message exactly states and demonstrate the algorithm used (usually in a programmatic fashion) will win a cash prize. I’ve learned over the years that I have been making it far too difficult by creating too many twists and turns; and assuming too much about the depth of the challengers. With careful gauging I’ve created an easy way to stymie some of the wittiest challengers. Out of the 7 crypto challenges I’ve posted this year only 2 of them won, and this is why…

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