More Matlab and RC4
June 5th 2009
A reader asked for more details on the RC4 and block cipher mode functions I wrote in Matlab.
To recap, I needed a ‘block cipher’ to produce a complete example of how a straight block cipher fails to hide large patterns in the output, and how an appropriate block cipher mode yields something akin to white noise.
Wikipedia has a “penguin” example with a block encrypted version (penguin still visible) and a block of white noise. The white noise represents what the block mode output is supposed to look like as opposed to being the genuine output of a block cipher mode. So I built this ‘real’ example, more or less.
I didn’t have a block cipher that worked with small blocks. But I knew it wasn’t hard to implement RC4. So I created a function to map 8 bytes of data into 8 bytes of ‘ciphertext’ to simulate the block cipher.