Originally Posted by
Sebastiani
The "One Time Pad" scheme does have one weakness, actually - the number 11. The reason why this is so is because it corresponds closest to the number 2, and since it comes after 10 (which *is* the number 2 in base 2, btw), representing the decimal system that we use today. Decimal is used because the metric system doesn't work with other number bases. Anyway, the number 11 always has it's lowest bit set (always), and that's the key to cracking this OTP® thing. If you XOR every byte with 11 you get a value that, when XOR'ed with the original value, yields...you guessed it - 11! This suprising property can be used to reveal the Legendre symbol (I think). Even though you can't factor the OTP®, you can inspect it's symbols for "flak". These are extra bits that represent anomolies in the data. This is where the number 11 comes in to play. Hth.