MAUGE Vincent wrote: > > Concerning cryptography : > > I also notice that XOR 2 osos gives a high-entropy files. However, RC4 > is a generator of random bytes xor with clear text. So if we make : > > osos_encrypted_1 xor osos_encrypted_2 = (osos_clear_1 xor key) xor > (osos_clear_2 xor key) > = osos_clear_1 xor osos_clear_2
Just to be totally complete in this study we should also get the xor of two ARM9 binaries and compare the frequency analysis of this xor to the frequency analysis of the xored ciphered payload. > Does anybody know a stream cipher that allow to reuse the same key ? I > mean that the next encrypted char depends of all the previous char > encrypted and not only the number of encrypted char (such as RC4) No, it's simply not possible. The only option, if the result of this study is that no information leak from the xor, is that they are using a *block cipher*. Indeed, in the case of a block cipher the next block is ciphered by using the current block meaning that the clear text is also part of the key (you change the text, you change the key). For more details see: http://en.wikipedia.org/wiki/Block_cipher. Regards -- Emmanuel Fleury | Office: 261 Associate Professor, | Phone: +33 (0)5 40 00 69 34 LaBRI, Domaine Universitaire | Fax: +33 (0)5 40 00 66 69 351, Cours de la Libération | email: [EMAIL PROTECTED] 33405 Talence Cedex, France | URL: http://www.labri.fr/~fleury _______________________________________________ Linux4nano-dev mailing list [EMAIL PROTECTED] https://mail.gna.org/listinfo/linux4nano-dev http://www.linux4nano.org
