demangle-epub-fonts.epub

#!/bin/python

import os, sys, hashlib

def main():
    progname = 'epub-font-obfuscation'
    algorithms = {'idpf': 1040, 'adobe': 1024}

    if len(sys.argv) > 2:
        uid = sys.argv[1]
    else:
        sys.exit(f'usage: {progname} key algorithm://font...')

    for fname in sys.argv[2:]:
        for algorithm in algorithms:
            if fname.startswith(algorithm + '://'):
                a = algorithm

        if not a:
            sys.exit('unable to determine obfuscation method\n')

        fname = fname.removeprefix(a + '://')

        if a == 'adobe':
            key = bytearray.fromhex(uid.removeprefix('urn:uuid:').replace('-', ''))
        else:
            key = bytearray(hashlib.sha1(uid.encode()).digest())

        s = len(key)

        if not os.path.exists(fname):
            print(f'{progname}: warning: {fname}: no such file', file=sys.stderr)
            continue

        with open(fname, 'rb+') as file:
            i = 0
            size = algorithms[a]

            for _ in range(size):
                byte = file.read(1)
                file.seek(file.tell() - 1)

                if byte:
                    file.write((byte[0] ^ key[i % s]).to_bytes(1, 'little'))
                    i += 1

if __name__ == '__main__':
    main()