otrdecoder is an opensource tool for decoding .otrkey files from https://www.onlinetvrecorder.com/. It tries to be compatible with the command line programs from them. Currently it’s limited to decoding, the extended features are not implemented.
It’s based on otrtool (https://github.com/otrtool/otrtool),
but ported from C to Python. The decoding algorithm was
reverse-engineered by eddy14, it’s described in his blog
(German, mirrored by PyroPeter):
http://pyropeter.eu/41yd.de/blog/2010/04/18/otrkey-breaker/ , Google Translate
It depends on Python, both v2.7 and v3.x are supported.
Furthermore it needs PyCryptodome, install that with
pip install pycryptodome
usage: otrdecoder [-h] [-v] -i FILE -e EMAIL -p PASSWORD [-o OUTDIR] [-f] [-q] optional arguments: -h, --help, -? prints this screen -v prints version -i FILE use FILE as input file -e EMAIL use EMAIL to fetch the key directly from otr -p PASSWORD use PASSWORD to fetch the key directly from otr -o OUTDIR use OUTDIR as output directory (default: .) -f force overwriting of output file -q don't verify input file before processing.
The performance is comparable to the compiled programs. Decoding is a little bit slower, as the .otrkey files are using little-endian blowfish encryption. PyCryptodome supports only the standard big-endian blowfish, so the data has to be endian swapped before and after the encryption. otrtool can directly decrypt the little-endian blowfish, saving this swapping.
Furthermore otrtool verifies the data during the decoding, while this program uses extra verify passes. That’s done to be compatible to the original program.