TIK/ofp_mtk_decrypt.py

#!/usr/bin/env python3
# Oppo OFP MTK Decrypter (c) B. Kerler 2022
# Licensed under MIT License

import os
import sys
import hashlib
from Crypto.Cipher import AES
from struct import unpack
from binascii import unhexlify, hexlify


def swap(ch):
    return ((ch & 0xF) << 4) + ((ch & 0xF0) >> 4)


def keyshuffle(key, hkey):
    for i in range(0, 0x10, 4):
        key[i] = swap((hkey[i] ^ key[i]))
        key[i + 1] = swap(hkey[i + 1] ^ key[i + 1])
        key[i + 2] = swap(hkey[i + 2] ^ key[i + 2])
        key[i + 3] = swap(hkey[i + 3] ^ key[i + 3])
    return key


def mtk_shuffle(key, keylength, input, inputlength):
    for i in range(0, inputlength):
        k = key[(i % keylength)]
        h = ((((input[i]) & 0xF0) >> 4) | (16 * ((input[i]) & 0xF)))
        input[i] = k ^ h
    return input


def mtk_shuffle2(key, keylength, input, inputlength):
    for i in range(0, inputlength):
        tmp = key[i % keylength] ^ input[i]
        input[i] = ((tmp & 0xF0) >> 4) | (16 * (tmp & 0xF))
    return input


def aes_cfb(key, iv, data, decrypt=True, segment_size=128):
    cipher = AES.new(key, AES.MODE_CFB, IV=iv, segment_size=segment_size)
    if decrypt:
        plaintext = cipher.decrypt(data)
        return plaintext
    else:
        ciphertext = cipher.encrypt(data)
        return ciphertext


keytables = [
    ["67657963787565E837D226B69A495D21",  # A77 CPH1715EX_11_A.04_170426, F1S A1601_MT6750_EX_11_A.15_160913 FW
     "F6C50203515A2CE7D8C3E1F938B7E94C",
     "42F2D5399137E2B2813CD8ECDF2F4D72"],

    ["9E4F32639D21357D37D226B69A495D21",  # A77 CPH1715EX_11_A.04_170426, F1S A1601_MT6750_EX_11_A.15_160913 CDT
     "A3D8D358E42F5A9E931DD3917D9A3218",
     "386935399137416B67416BECF22F519A"],

    ["892D57E92A4D8A975E3C216B7C9DE189",
     "D26DF2D9913785B145D18C7219B89F26",
     "516989E4A1BFC78B365C6BC57D944391"],

    ["27827963787265EF89D126B69A495A21",
     "82C50203285A2CE7D8C3E198383CE94C",
     "422DD5399181E223813CD8ECDF2E4D72"],

    ["3C4A618D9BF2E4279DC758CD535147C3",
     "87B13D29709AC1BF2382276C4E8DF232",
     "59B7A8E967265E9BCABE2469FE4A915E"],

    ["1C3288822BF824259DC852C1733127D3",  # A83_CPH1827_11_A.21_2G_180923 FW, Realme 3 RMX1827EX_11_C.13_200624_1264686e
     "E7918D22799181CF2312176C9E2DF298",
     "3247F889A7B6DECBCA3E28693E4AAAFE"],

    ["1E4F32239D65A57D37D2266D9A775D43",
     "A332D3C3E42F5A3E931DD991729A321D",
     "3F2A35399A373377674155ECF28FD19A"],

    ["122D57E92A518AFF5E3C786B7C34E189",
     "DD6DF2D9543785674522717219989FB0",
     "12698965A132C76136CC88C5DD94EE91"],

    [
        "ab3f76d7989207f2",  # AES KEY
        "2bf515b3a9737835"  # AES IV
    ]

]


def getkey(index):
    kt = keytables[index]
    if len(kt) == 3:
        obskey = bytearray(unhexlify(kt[0]))
        encaeskey = bytearray(unhexlify(kt[1]))
        encaesiv = bytearray(unhexlify(kt[2]))
        aeskey = hexlify(hashlib.md5(mtk_shuffle2(obskey, 16, encaeskey, 16)).digest())[:16]
        aesiv = hexlify(hashlib.md5(mtk_shuffle2(obskey, 16, encaesiv, 16)).digest())[:16]
    else:
        aeskey = bytes(kt[0], 'utf-8')
        aesiv = bytes(kt[1], 'utf-8')
        print(aeskey, aesiv)
    return aeskey, aesiv


def brutekey(rf):
    rf.seek(0)
    encdata = rf.read(16)
    for keyid in range(0, len(keytables)):
        aeskey, aesiv = getkey(keyid)
        data = aes_cfb(aeskey, aesiv, encdata, True)
        if data[:3] == b"MMM":
            return aeskey, aesiv
    print("Unknown key. Please ask the author for support :)")
    exit(0)


def cleancstring(input):
    return input.replace(b"\x00", b"").decode('utf-8')


def main(filename, outdir):
    if not os.path.exists(outdir):
        os.mkdir(outdir)
    hdrkey = bytearray(b"geyixue")
    filesize = os.stat(filename).st_size
    hdrlength = 0x6C
    with open(filename, 'rb') as rf:
        aeskey, aesiv = brutekey(rf)
        rf.seek(filesize - hdrlength)
        hdr = mtk_shuffle(hdrkey, len(hdrkey), bytearray(rf.read(hdrlength)), hdrlength)
        prjname, unknownval, reserved, cpu, flashtype, hdr2entries, prjinfo, crc = unpack("46s Q 4s 7s 5s H 32s H", hdr)
        hdr2length = hdr2entries * 0x60
        prjname = cleancstring(prjname)
        prjinfo = cleancstring(prjinfo)
        cpu = cleancstring(cpu)
        flashtype = cleancstring(flashtype)
        if prjname != "": print(f"Detected prjname:{prjname}")
        if prjinfo != "": print(f"Detected prjinfo:{prjinfo}")
        if cpu != "": print(f"Detected cpu:{cpu}")
        if flashtype != "": print(f"Detected flash:{flashtype}")

        rf.seek(filesize - hdr2length - hdrlength)
        hdr2 = mtk_shuffle(hdrkey, len(hdrkey), bytearray(rf.read(hdr2length)), hdr2length)
        for i in range(0, len(hdr2) // 0x60):
            name, start, length, enclength, filename, crc = unpack("<32s Q Q Q 32s Q", hdr2[i * 0x60:(i * 0x60) + 0x60])
            name = name.replace(b"\x00", b"").decode('utf-8')
            filename = filename.replace(b"\x00", b"").decode('utf-8')
            print(f"Writing \"{name}\" as \"{outdir}/{filename}\"...")
            with open(os.path.join(outdir, filename), 'wb') as wb:
                if enclength > 0:
                    rf.seek(start)
                    encdata = rf.read(enclength)
                    if enclength % 16 != 0:
                        encdata += b"\x00" * (16 - (enclength % 16))
                    data = aes_cfb(aeskey, aesiv, encdata, True)
                    wb.write(data[:enclength])
                    length -= enclength
                while length > 0:
                    size = 0x200000
                    if length < size:
                        size = length
                    data = rf.read(size)
                    length -= size
                    wb.write(data)

    print(f"Files successfully decrypted to subdirectory {outdir}")


if __name__ == '__main__':
    if len(sys.argv) != 3:
        print("Oppo MTK OFP decrypt tool 1.1 (c) B.Kerler 2020-2022\n")
        print("Usage: %s <filename> <directory to extract>" % __file__)
        sys.exit(1)

    filename = sys.argv[1]
    outdir = sys.argv[2]
    main(filename, outdir)