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Physical Store Private Key Derivation

Background

As described in the TSforge blogpost, the AES key needed to decrypt the physical store's contents is encrypted using an RSA whitebox located in a component known as the blackbox/secure processor (spsys.sys on Windows Vista/7, part of sppsvc.exe on Windows 8+). Luckily, with a debugger and a basic understanding of the math behind RSA, the private key of this whitebox can be easily extracted, allowing exploits like ZeroCID to be carried out on an unmodified system.

SpModExpPrv

In the symbols for spsys.sys in Windows 8 build 7850, the whitebox is named SpModExpPrv. This function only implements plain RSA decryption with a constant private key, and other code is used to implement operations such as padding and RSA encryption.

WitherOrNot

from Crypto.Cipher import ARC4
from hashlib import sha1, md5
from random import randint
from ecutils.core import Point, EllipticCurve
from sys import argv

KCHARS = "BCDFGHJKMPQRTVWXY2346789"

SPK_ECKEY = {
    "a": 1,

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