Rockbox mail archive
Subject: Re: Descrambler for multimedia
From: Josh Nisly (joshn_at_invtools.com)
Does this mean that the focus for new Rockbox "expansion" will change
from mp3 players from other manufacturers (Neo, xclef players) to Archos
Björn Stenberg wrote:
>My little christmas project has paid off. I just committed an update to 'descrambler' which supports descrambling Multimedia firmware files. I'll commit a new 'scrambler' tomorrow.
>The Multimedia firmware files are compressed using a custom token packing algorithm, and then XORed with a 32-byte string. The descrambler tool finds this string automagically, simply by assuming that 0 is the most common byte in the plaintext. A simple statistical analysis then produces the string.
>The compression was trickier, but thanks to it not being very efficient (gzip compresses the firmware to about 60% of the .ajz size) there was plenty of plaintext to look at in the compressed data.
Page was last modified "Jan 10 2012" The Rockbox Crew