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scramble.pl

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NAME

scramble.pl - Scramble an mp3 file by reordering frames randomly

SYNOPSIS

scramble.pl inputfile.mp3

DESCRIPTION

scramble.pl is a Perl script that randomizes the order of all the frames in inputfile.mp3, saving the edits to the output file scramble.mp3. scramble.pl is part of the main mpgedit regression test test1.pl, or can be called as a stand-alone program. scramble.pl is an mpgedit torture test, but it can also be used for obscuring the contents of an mp3 file. The original input file can later be recovered by calling the reciprocal operation unscramble.pl.

These are the steps scramble.pl follows to generate the scramble.mp3 file:

Save off the last frame of inputfile.mp3 to the file scramble_x.mp3 for later use. This must be done because the time duration of this frame is likely to be less than a full frame time of 26ms, and will throw off the unscramble operation when it appears somewhere in the middle of scramble.mp3

Create a scrambled list of start/stop times for each frame in inputfile.mp3 by calling the Perl script scramble_times.pl. The list of scrambled start/stop times is saved to the file scramble.out for later use by unscramble.pl.

Perform a series of 40-single frame edits controlled by the start/stop times listed in the scramble.out file. These edits are all appended to the output file scramble.mp3.

Append the saved final frame scramble_x.mp3 to the now scrambled output saved in the file scramble.mp3.

The resultant scrambled output file is now completely unintelligible when played back. The only use for this file is as input to the unscramble.pl test script. Recovery of the scramble file scramble.mp3 is easily accomplished by running ./unscramble.pl. The unscrambled output is saved to the file descramble.mp3.

BUGS

The final frame of inputfile.mp3 always appears as the final frame of scramble.mp3. The scramble start/stop times are always saved to scramble.out. The loss or modification of this file makes recovery of descramble.mp3 impossible. Any ID3 tags present in inputfile.mp3 are edited away by the scramble/unscramble operation.