Unpack .etq and .lpg files used by hamradiotrainer

unpack_etq.py

#!/usr/bin/env python3

import struct
import sys
import hashlib
import zlib

with open("./hamradiotrainer.exe", "rb") as fh:
    key = fh.read()
assert hashlib.sha256(key).hexdigest() == "b1615d0efc0ee2d1a1714df0dbb1eb3d1283c075db19e8b032044231303d3ae5"
key = key[0x149344:0x149344+59]

with open(sys.argv[1], "rb") as fh:
    magic = fh.read(8)
    assert magic == b"ETQ1\0\0\0\0"

    while True:
        magic = fh.read(4)
        if len(magic) == 0:
            break
        assert magic == b"FI2\0"

        rlen, flags = struct.unpack(">II", fh.read(8))
        is_compressed = flags & (1 << 16) != 0
        is_encrypted = flags & 1 != 0

        md5 = fh.read(16)

        fname_len = struct.unpack(">H", fh.read(2))[0]
        fname = fh.read(fname_len)
        assert len(fname) == fname_len
        fname = fname.decode("ascii")

        fsize = rlen - 4 - 16 - 2 - fname_len
        fcontents = fh.read(fsize)
        assert len(fcontents) == fsize
        assert hashlib.md5(fcontents).digest() == md5

        if not is_encrypted:
            plaintext = fcontents
        else:
            i = fsize
            j = (i >> 3) & 7
            j += 3 if j == 0 else 0
            plaintext = []
            for x in fcontents:
                x -= key[i % len(key)]
                x += 0x100 if x < 0 else 0
                plaintext.append(x)
                i += j
            plaintext = bytes(plaintext)

        if is_compressed:
            unc_size = struct.unpack(">I", plaintext[:4])[0]
            plaintext = zlib.decompress(plaintext[4:])
            assert len(plaintext) == unc_size

        safe_fname = fname.replace("/", "_")
        with open(safe_fname, "wb") as ofh:
            ofh.write(plaintext)

        print(fname, len(plaintext), plaintext[:16])