Tool to unscrew Terramaster encrypted PHP files.

unscrew.py

#!/usr/bin/env python3
#
# This script decrypts the PHP files for the web UI of TerraMaster NAS devices.
# The technique used for the encryption is a slighly modified version of the
# "screw-plus" tool version 1.5. The TerraMaster variant differs only by an
# additional XOR scrambling pass on the ciphertext on top of the AES-CBC
# encryption step. The XOR mask used is the ASCII code of the last character
# of the PHP file name (extension excluded).
# Files are decrypted in place.
#
# Author: @bloodyshell:matrix.org
# License
# This is free and unencumbered software released into the public domain.
#
# Anyone is free to copy, modify, publish, use, compile, sell, or
# distribute this software, either in source code form or as a compiled
# binary, for any purpose, commercial or non-commercial, and by any
# means.
#
# In jurisdictions that recognize copyright laws, the author or authors
# of this software dedicate any and all copyright interest in the
# software to the public domain. We make this dedication for the benefit
# of the public at large and to the detriment of our heirs and
# successors. We intend this dedication to be an overt act of
# relinquishment in perpetuity of all present and future rights to this
# software under copyright law.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
# IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
# OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
# ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
# OTHER DEALINGS IN THE SOFTWARE.
#
# For more information, please refer to <http://unlicense.org/>
    
from cryptography.hazmat.primitives.ciphers.modes import CBC
from cryptography.hazmat.primitives.ciphers import Cipher
from cryptography.hazmat.primitives.ciphers.algorithms import AES
from hashlib import md5
import os


# root@a:/usr/www# strings /usr/lib/php/php_terra_master.so | grep -A1 /proc/self/fd/ | tail -n1 
# GH65Hws2jedf3fl3MeK

TERRAMASTER_PASSWORD = "GH65Hws2jedf3fl3MeK"

def unscrew(infilename, outfilename, password, descramble=False):
    # The hex representation of the MD5 hash of the password is used as the
    # AES encryption key
    key = bytes(md5(bytes(password, "utf-8")).hexdigest(), "ascii")
    # The first half of the key is used as the IV for CBC
    iv = key[:16]
    
    with open(infilename, "rb") as inf:
        body = inf.read()
    
    # The IV is stored in the first 16 bytes of the encrypted file
    if body[:16] != iv:
        return False
    
    # The next 16 bytes contain the ASCII representation of the decimal value
    # of the plaintext length padded with null bytes
    plaintext_len = 0
    for b in body[16:31]:
        if ord('0') <= b <= ord('9'):
            plaintext_len = plaintext_len * 10 + b - ord('0') 
        else:
            break
    
    # Descramble the ciphertext if necessary
    if descramble:
        if descramble == True:
            # The TerraMaster scramble mask is the ASCII value of the last
            # character of the filename before the ".php" extension:
            # Ex.: "index.php" will have a scramble mask of ord('x') (120)
            scramble_key = ord(infilename[-5])
        else:
            scramble_key = descramble
        ciphertext = bytes([x ^ scramble_key for x in body[32:]])
    else:
        ciphertext = body[32:]
    
    # Regular AES256-CBC decryption
    decryptor = Cipher(AES(key), CBC(iv)).decryptor()
    plaintext = decryptor.update(ciphertext)
    plaintext += decryptor.finalize()
    
    with open(outfilename, "wb") as outf:
        outf.write(plaintext[:plaintext_len])
    
    return True
    
    
def do_unscrew(path, password, descramble):
    if not os.path.exists(path):
        return
    elif os.path.isfile(path):
        r = unscrew(path, path, password, descramble)
        if r:
            print(f"{path} unscrewed successfully")
    elif os.path.isdir(path):
        for base, dirs, files in os.walk(path):
            for fn in files:
                fpath = os.path.join(base, fn)
                if not os.path.exists(fpath):
                    continue
                r = unscrew(fpath, fpath, password, descramble)
                if r:
                    print(f"{fpath} unscrewed successfully")
    
    
if __name__ == "__main__":
    import argparse
    
    parser = argparse.ArgumentParser(description="Unscrew PHP source files")
    parser.add_argument("files_or_dirs", nargs="+")
    parser.add_argument("--password", "-p", default=TERRAMASTER_PASSWORD)
    parser.add_argument("--descramble", "-d", default="terramaster")
    args = parser.parse_args()
    
    d = args.descramble.lower()
    
    if d in ("terramaster", "yes", "true"):
        descramble = True
    elif d in ("none", "no", "false"):
        descramble = False
    else:
        descramble = int(descramble)
    
    for fn in args.files_or_dirs:
        do_unscrew(fn, args.password, descramble)