Cryptography : is it me ???

[fullmetalcoder]

No, it's not "generated" from key, it's part of the key. Consider the key to be made of two parts - one is the S-box number used and the other is the seed for the key stream generator.

Generally the idea is that n changes every block and you don't know which S-box is used, so you can't follow the pattern - you have to check every S-box. The larger the number of S-boxes, the better the security. Additionally you can introduce another level - switch S-boxes during computation.

Of course all that makes the cipher quite computation intensive and hard to implement in hardware.

My goal here is not to obtain the most secure algorithm ever... I need something simple and fast enough to be describe as an appendix of my paper... I can't afford a long and complicated stuff because it is not a paper on computer science in particular but on math in general and even if I was free to choose any math-related topic there are some limits...

So here comes the fun. The link below points to a XOR encrypted version of my paper in its current state. I use the last version of the algorithm I proposed so all you have to do is to break the first block. However there are some difficulties :

• AFAIK the only way to break it is a brute-force attack or a stunning luck...
• The key is rather big say between 15 and 25 chars => 120 and 200 bits => quite a number of possibilities...
• The input data is compressed due to the file format used (a "all-in one" document with text formatting and embedded images...)

However you have some insights : it's written in english, it deals with "algorithms", "computational complexity", "cryptography", ...

The encrypted file!

Good luck to the ones who won't be able to resist and attempt to crack it!

P.S : if you managed to break the code may you take a look at it and report mistakes in the content or the expression (english is not my native language...)