otp_fixer.py

from pyctr.crypto import CryptoEngine
from Cryptodome.Cipher import AES
from hashlib import sha256

a = CryptoEngine()

def print_diff(ori, enc, dec, postxt, *suffix):
    if postxt == None:
        return
    if type(postxt) is tuple:
        s = len(enc) // len(postxt)
        for x in range(len(enc) // s):
            b, e = x * s, (x + 1) * s
            xori, xenc, xdec = ori[b:e], enc[b:e], dec[b:e]
            if xori != xenc:
                print(f"{postxt[x]} ori:", xori.hex(), *suffix)
                print(f"{postxt[x]} fix:", xenc.hex(), xdec.hex(), *suffix)
    elif ori != enc:
        print(f"{postxt} ori:", ori.hex(), *suffix)
        print(f"{postxt} fix:", enc.hex(), dec.hex(), *suffix)

def decrypt_otp_block(data, iv):
    cipher = AES.new(a.otp_key, AES.MODE_CBC, iv)
    return cipher.decrypt(data)

def crack_singlebit(indata, iv, check, postxt):
    #if check(decrypt_otp_block(indata, iv)):
    #    return indata
    ret = None
    ints = bytearray(indata)
    for x in range(len(indata)):
        orig = ints[x]
        for bit in range(8):
            new = orig ^ (1 << bit)
            ints[x] = new
            data = decrypt_otp_block(ints, iv)
            if check(data):
                print_diff(indata, ints, data, postxt, "(single bit)")
                ret = ints
                return ret
        ints[x] = orig
    return ret

def crack_dataline(indata, iv, bit, check, postxt):
    #if check(decrypt_otp_block(indata, iv)):
    #    return indata
    set_size = len(indata) // 4
    ret = None
    for combi in range(pow(2, set_size)):
        ints = bytearray(indata)
        for addr in range(set_size):
            if (combi >> addr) & 1:
                byte = 4 * addr + bit // 8
                orig = ints[byte]
                ints[byte] = orig ^ (1 << (bit % 8))
        cipher = AES.new(a.otp_key, AES.MODE_CBC, iv)
        data = cipher.decrypt(ints)
        if check(data):
            print_diff(indata, ints, data, postxt, "(data line)")
            ret = ints
            return ret
    return ret

def crack_singlebit_dataline(indata, extract, check, postxt, bit = -1):
    indata, iv = extract(indata)
    ret = (-1, b"\x00" * len(indata))

    if check(decrypt_otp_block(indata, iv)):
        if bit == -1:
            bit = -2
        return (bit, indata)

    if bit == -1 or bit == 32:
        res = crack_singlebit(indata, iv, check, postxt)
        if res != None:
            ret = (32, res)
            return ret
        #if bit == 32:  # force sigle bit -> fail
        #    return ret

    if bit < 0:  # -1: default, -2: no need to fix previously
        for bit in range(32):
            res = crack_dataline(indata, iv, bit, check, postxt)
            if res != None:
                ret = (bit, res)
                return ret
    else:
        res = crack_dataline(indata, iv, bit, check, postxt)
        if res != None:
            ret = (bit, res)
            return ret

    return ret

def crack0x00(otp2fix):
    def extract(data):
        return data[0:0x10], a.otp_iv

    def check(data):
        return data[0:4] == b"\x0f\xb0\xad\xde" and data[0xD:0x10] == b"\x00\x00\x00" and data[0xC] in (0, 2)

    ret = crack_singlebit_dataline(otp2fix, extract, check, "0x00")
    if ret[0] == -1:
        print("Can't fix 0x00")
        exit(1)
    return ret

def crack0x10(otp2fix, bit):
    def extract(data):
        return data[0x10:0x20], data[0:0x10]

    def check(data):
        return data[0x8:0xA] == b"\x05\x00"

    ret = crack_singlebit_dataline(otp2fix, extract, check, "0x10", bit)
    if ret[0] == -1:
        print("Can't fix 0x10")
        exit(1)
    return ret

def crack0x70x80(otp2fix, bit):
    def extract(data):
        return data[0x70:0x90], data[0x60:0x70]

    def check(data):
        return data[0x10:0x20] == b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"

    ret = crack_singlebit_dataline(otp2fix, extract, check, ("0x70", "0x80"), bit)
    if ret[0] == -1:
        print("can't fix 0x70, 0x80")
        #exit(1)
    return ret

def showbits(bit):
    for addr in range(0x100 // 4):
        byte = 4 * addr + bit // 8
        orig = otp[byte]
        print((orig >> (bit % 8)) & 1, end="\t")
        if addr % 4 == 3:
            print()

with open('otp.mem', 'rb') as f:
    content = f.read(0x100)

otp = bytearray(content)

bit, otp[0:0x10] = crack0x00(otp)
#showbits(bit)
bit, otp[0x10:0x20] = crack0x10(otp, bit)
bit, otp[0x70:0x90] = crack0x70x80(otp, bit)

#showbits(bit)


print(f"Bit: {bit}")
for x in range(0x10):
    print("--------------------------------")
    start = 0x10 * x
    end = start + 0x10
    print(content[start:end].hex())
    print(otp[start:end].hex())

with open('otp_fixed.mem', 'wb') as f:
    f.write(otp)

#for bit in range(32):
#    ints = bytearray(content[0:0x10])
#    for combi in range(pow(2, 0x10 // 4)):
#        for addr in range(0, 0x10, 4):
#            if (combi >> addr) & 1:
#                byte = addr + bit // 8
#                orig = ints[byte]
#                ints[byte] = orig ^ (1 << (bit % 8))
#        cipher = AES.new(a.otp_key, AES.MODE_CBC, a.otp_iv)
#        data = cipher.decrypt(ints)
#        ohash = data[0xE0:]
#        before_hash = data[0:0xE0]
#        hash_before_hash = sha256(before_hash).hexdigest()
#        if data[0:4].hex() == "0fb0adde":
#            print(data[0:4].hex(), bit, combi)
#        #print(bit, hash_before_hash, ohash.hex(), hash_before_hash == ohash.hex())
#        if hash_before_hash == ohash.hex():
#            print(beginning + before_hash + ohash)