Wednesday, June 09, 2004

It's still rockin' XOR to me.

Boing Boing has a post about a program which takes two arbitrary binary files and "munges" them into a third binary file. It can then take any two of those three files and produce the missing file.

It sounds to me like a simple XOR! Moreover, I'm sure I've heard this idea before. I searched a little.

In 2000, Slashdot posted a link to "A method of free speech on the Internet: random pads" which describes using XOR to hide file contents.

In 1995, RISKS-FORUM Digest had a message from Erann Gat titled "The source of semantic content." In it, Erann describes a way to transmit forbidden content using a one-time pad. The resulting thread has interesting discussion.

Erann claims that people using this system would be able to deny that they were propagating forbidden content. Barry Margolin points out, "unless they actually didn't know what the purpose of those random bit streams were, they would be perjuring themselves." David Harpe says, "During the trial, the reconstructed image is all the jury will see, understand or remember. They will fall asleep during the expert witness testimony regarding public key cryptography."

I have two remarks of my own. One is that it's interesting how in nine years "forbidden content" went from pornography to copyrighted works, and it may be about to go back.

The second thing this brings up to me is the nature of computer evidence in court. The police can seize my computer and tell the court that they found on it whatever they want to say. I have no way to prove that the evidence was planted. Of course, this isn't that different from the past. It's not more difficult to plant information on a computer than it is to plant damning paper.
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