README.md

EAC Log Signer

This is a transparent implementation of the Exact Audio Copy log checksum algorithm in Python 3.6+. Includes an option to fix those pesky edited logs.

Installation

Only depends on pprp (for an implementation of Rijndael-256 with variable block sizes):

$ pip install pprp
$ curl https://raw.githubusercontent.com/puddly/eac_logsigner/master/eac.py > eac_logsigner
$ chmod +x eac_logsigner

Usage

usage: eac.py [-h] {verify,sign} ...

Verifies and resigns EAC logs

positional arguments:
  {verify,sign}
    verify       verify a log
    sign         sign or fix an existing log

optional arguments:
  -h, --help     show this help message and exit

Example

$ python3 eac.py sign bad.log good.log
$ python3 eac.py verify *.log
log1.log:  OK
log2.log:  OK
log3.log:  Malformed

Algorithm

1. Strip the log file of newlines and BOMs.
2. Cut off the existing signature block and (re-)encode the log text back into little-endian UTF-16
3. Encrypt the log file with Rijndael-256:
   • in CBC mode
   • with a 256-bit block size (most AES implementations hard-code a 128-bit block size)
   • all-zeroes IV
   • zero-padding
   • the hex key 9378716cf13e4265ae55338e940b376184da389e50647726b35f6f341ee3efd9
4. XOR together all of the resulting 256-bit ciphertext blocks. You can do it byte-by-byte, it doesn't matter in the end.
5. Output the little-endian representation of the above number, in uppercase hex.