Ethics: Codes

[mith]

Indeed, if what you're talking about is a one-time pad, you can just make up an approrpriate key later on.

Another XOR code possibility would be to split your claim into two pieces and XOR them against each other. This is much more difficult (nearly impossible) to fake, but is also more vulnerable to being broken.

[VisMaior]

If I'm not mistaken, with XOR encryption, you can make up a key afterward that turns the encrypted post into absolutely any message you want.

Right, but not if you have a password of minimal length (like, 8 chars or so) and repeat the word over and over. No real problem, people using a key as long as the messge iotself are claiming false.

[mith]

Ah, you mean Vigenère. That's pretty vulnerable, at least for a long enough message.

[Fiasco]

That does seem like it would work, but maybe there's some sort of clever way to find a few different meaningful messages that could be turned to the same code using different repeating keys? It seems unlikely, but with RSA you have a full guarantee.

edit: Mith: how long is "long enough"? With just a few lines of encoded text available, is there any chance to break it in practice? I'd guess not.

[VisMaior]

Vigenère, no, I dont mean that. Exclusive-OR, thats what I mean.

For every bit in the encrypted data we take the appropriate bit in the ley. If Keybit(n)==1, we invert the textbit. Otherwise we do nothing.

Basically, its a bitwise XOR operation between the text and the key. Unbreakable without the key, as the information in every bit of the text is exactly half a bit. No correlatiopn whatsoever with the next bit. With short keys repetitively added it shows some degree of vulnerability, wich is actually dispatched quiet easily, but for the purposes of a forum game, it should proove unbreakable even so.

[mith]

I know what XOR means...

What I mean is it's essentially identical to Vigenère. As you've stated there, it's certainly not unbreakable, and is in fact quite vulnerable. But sure, you can modify it various ways to make it secure (though if you're going to do that, it's really no simpler to use than RSA).

[Norinel]

The evil me wants to run the game where everyone's first post has their RSA public key.

The good me wants to run the game set in a high-tech future where it's in the rules that all the players have the near-infinite computing power required to break anything that can be decrypted in bounded time.

[ralphmerridew]

Regarding XOR:

If you're allowed to use a random key as long as the message, it's unbreakable, but useless because the mafia can choose a key that will decrypt to any message they want.

If you use grammatically correct English text for the key, then the message can probably be broken with a moderate amount of effort.

(Once somebody XORed two sentences against each other and gave the result; I was able to work out the originals in about an hour.)