Decrypt Krux encrypted mnemonics from QR codes or json files

krux_decrypt.py

# The MIT License (MIT)

# Copyright (c) 2021-2023 Krux contributors

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.

# 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 OR COPYRIGHT HOLDERS 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.

# Python requirements: pycryptodome, opencv-python, pyzbar, embit
#  pip install pycryptodome opencv-python pyzbar embit
# OS may require: zbar-tools (sudo apt install zbar-tools)

# Usage:

# Decrypt a mnemonic from a json file:
#  python krux_decrypt.py json --file seeds.json
# <seeds.json> can be a path

# Scan and decrypt an encrypted mnemonic QR code:
#  python krux_decrypt.py qr

# Brute force mode for encrypted mnemonic QR codes: 
#  python krux_decrypt.py qr --bf
# Use this mode only if you were affected by a bug on v23.09.0 where user could set a custom PBKDF2 iterations value,
# which was not multiple of 10,000, and Krux would fail to decrypt the encrypted mnemonic QR code created with this setting.
# This mode will brute force PBKDF2 iteration values in a possible range until it finds the correct one.
# This has nothing to do with key bruteforcing, it will only work with correct key.


import time
import hashlib
import base64
import argparse
import json
from Crypto.Cipher import AES
import cv2
from pyzbar.pyzbar import decode
from embit import bip39


PBKDF2_HMAC_ECB = 0
PBKDF2_HMAC_CBC = 1
AES_BLOCK_SIZE = 16

VERSION_MODE = {
    "AES-ECB": AES.MODE_ECB,
    "AES-CBC": AES.MODE_CBC,
    PBKDF2_HMAC_ECB: AES.MODE_ECB,
    PBKDF2_HMAC_CBC: AES.MODE_CBC,
}

VERSION_NUMBER = {
    "AES-ECB": PBKDF2_HMAC_ECB,
    "AES-CBC": PBKDF2_HMAC_CBC,
}


class AESCipher(object):
    """Helper for AES encrypt/decrypt"""

    def __init__(self, key, salt, iterations):
        self.key = hashlib.pbkdf2_hmac(
            "sha256", key.encode(), salt.encode(), iterations
        )

    def decrypt(self, encrypted, mode, iv=None):
        """Decrypt a base64 using AES MODE_ECB and return the value decoded as string"""
        if iv:
            decryptor = AES.new(self.key, mode, iv)
        else:
            decryptor = AES.new(self.key, mode)
        load = decryptor.decrypt(encrypted).decode("utf-8")
        return load.replace("\x00", "")

    def decrypt_bytes(self, encrypted, mode, i_vector=None):
        """Decrypt and return value as bytes"""
        if i_vector:
            decryptor = AES.new(self.key, mode, i_vector)
        else:
            decryptor = AES.new(self.key, mode)
        return decryptor.decrypt(encrypted)


class MnemonicStorage:
    """Handler of stored encrypted seeds"""

    def __init__(self, json_vault) -> None:
        self.stored = json_vault

    def list_mnemonics(self, sd_card=False):
        """List all seeds stored on a file"""
        mnemonic_ids = []
        for mnemonic_id in self.stored:
            mnemonic_ids.append(mnemonic_id)
        return mnemonic_ids

    def decrypt(self, key, mnemonic_id):
        """Decrypt a selected encrypted mnemonic from a file"""
        try:
            encrypted_data = self.stored.get(mnemonic_id)["data"]
            iterations = self.stored.get(mnemonic_id)["key_iterations"]
            version = self.stored.get(mnemonic_id)["version"]
        except:
            return None
        data = base64.b64decode(encrypted_data)
        mode = VERSION_MODE[version]
        if mode == AES.MODE_ECB:
            encrypted_mnemonic = data
            iv = None
        else:
            encrypted_mnemonic = data[AES_BLOCK_SIZE:]
            iv = data[:AES_BLOCK_SIZE]
        decryptor = AESCipher(key, mnemonic_id, iterations)
        words = decryptor.decrypt(encrypted_mnemonic, mode, iv)
        return words


class EncryptedQRCode:
    """Creates and decrypts encrypted mnemonic QR codes"""

    def __init__(self) -> None:
        self.mnemonic_id = None
        self.version = None
        self.iterations = None
        self.encrypted_data = None

    def public_data(self, data):
        """Parse and returns encrypted mnemonic QR codes public data"""
        mnemonic_info = "Encrypted QR Code:\n"
        try:
            id_length = int.from_bytes(data[:1], "big")
            self.mnemonic_id = data[1 : id_length + 1].decode("utf-8")
            mnemonic_info += "ID: " + self.mnemonic_id + "\n"
            self.version = int.from_bytes(data[id_length + 1 : id_length + 2], "big")
            version_name = [k for k, v in VERSION_NUMBER.items() if v == self.version][
                0
            ]
            mnemonic_info += "Version: " + version_name + "\n"
            self.iterations = int.from_bytes(data[id_length + 2 : id_length + 5], "big")
            self.iterations *= 10000
            mnemonic_info += "Key iter.: " + str(self.iterations)
        except:
            return None
        extra_bytes = id_length + 5  # 1(id length byte) + 1(version) + 3(iterations)
        if self.version == 1:
            extra_bytes += 16  # Initial Vector size
        extra_bytes += 16  # Encrypted QR checksum is always 16 bytes
        len_mnemonic_bytes = len(data) - extra_bytes
        if len_mnemonic_bytes not in (16, 32):
            print(len_mnemonic_bytes)
            return None
        self.encrypted_data = data[id_length + 5 :]
        return mnemonic_info

    def decrypt(self, key, brute_force_iterations=1):
        """Decrypts encrypted mnemonic QR codes"""
        start_time = time.time()
        mode = VERSION_MODE[self.version]
        if mode == AES.MODE_ECB:
            encrypted_mnemonic_data = self.encrypted_data
            i_vector = None
        else:
            encrypted_mnemonic_data = self.encrypted_data[AES_BLOCK_SIZE:]
            i_vector = self.encrypted_data[:AES_BLOCK_SIZE]
        brute_force_index = brute_force_iterations
        success = False
        while brute_force_index > 0:
            iterations = self.iterations + brute_force_iterations - brute_force_index
            decryptor = AESCipher(key, self.mnemonic_id, iterations)
            decrypted_data = decryptor.decrypt_bytes(
                encrypted_mnemonic_data, mode, i_vector
            )
            mnemonic_data = decrypted_data[:-AES_BLOCK_SIZE]
            checksum = decrypted_data[-AES_BLOCK_SIZE:]
            # Data validation:
            if brute_force_iterations > 1 and ((brute_force_index + 1) % 100 == 0):
                print("Checking iterations above:", iterations)
                elapsed = time.time() - start_time
                print("Elapsed:", str(int(elapsed)) + "s")
            if hashlib.sha256(mnemonic_data).digest()[:16] == checksum:
                if brute_force_iterations > 1:
                    print("Iteration:", iterations)
                    elapsed = time.time() - start_time
                    print("Elapsed:", str(int(elapsed)) + "s")
                success = True
                break
            brute_force_index -= 1

        return mnemonic_data if success else None


def scan():
    """Opens a scan window and uses cv2 to detect and decode a QR code, returning its data"""
    vid = cv2.VideoCapture(0)
    qr_data = None
    while True:
        # Capture the video frame by frame
        _, frame = vid.read()
        try:
            qr_data = decode(frame)
        except:
            qr_data = []
        # _, _, _ = detector.detectAndDecode(frame)
        if qr_data:
            break
        # Display the resulting frame
        cv2.imshow("frame", frame)
        if cv2.waitKey(1) & 0xFF == ord("q"):
            break
    vid.release()
    cv2.destroyAllWindows()
    return qr_data[0].data


parser = argparse.ArgumentParser(
    prog="krux_decrypt",
    description="Python script to decrypt Krux encrypted mnemonics",
)

subparsers = parser.add_subparsers(help="sub-command help", dest="command")
qr_parser = subparsers.add_parser("qr", help="scans an decrypt an encrypted QR code")
qr_parser.add_argument(
    "--bf", action=argparse.BooleanOptionalAction, help="Activate brute force mode"
)

file_parser = subparsers.add_parser(
    "json", help="loads and decrypt a mnemonic from a Krux encrypted .json file"
)
file_parser.add_argument("--file", dest="json_file", help="path to file to .json file")


args = parser.parse_args()
if args.command == "qr":
    iterations = 10000 if args.bf else 1
    _ = input("Press enter to scan an encrypted mnemonic")
    scanned_data = scan()
    encrypted_qr = EncryptedQRCode()
    print(encrypted_qr.public_data(scanned_data.decode().encode("latin-1")))
    typed_key = input("Enter decryption key: ")

    binary_mnemonic = encrypted_qr.decrypt(typed_key, iterations)
    if binary_mnemonic:
        print(bip39.mnemonic_from_bytes(binary_mnemonic))
    else:
        print("Failed to decrypt")
elif args.command == "json":
    if args.json_file is None:
        print("Please specify a file")
    else:
        json_file = open(args.json_file, "r")
        json_vault = json.loads(json_file.read())
        json_file.close()
        vault = MnemonicStorage(json_vault)
        print("Stored Mnemonics:")
        stored_mnemonics = vault.list_mnemonics()
        for i, mnemonic in enumerate(stored_mnemonics):
            print(str(i) + ":", mnemonic)
        valid_index = False
        while not valid_index:
            try:
                mnemonic_index = int(
                    input("Enter the index of the mnemonic you wish to decrypt: ")
                )
                valid_index = True
            except:
                print("Please enter a integer number")
        typed_key = input("Enter decryption key: ")
        binary_mnemonic = vault.decrypt(typed_key, stored_mnemonics[mnemonic_index])
        print(binary_mnemonic)


else:
    parser.print_help()

at line 164 as/of revision #2:

• from self.iterations + brute_force_iteractions - brute_force_index - 1
• to self.iterations + brute_force_iteractions - brute_force_index
  so that iterating a single time on the exact iteration will decrypt the seed.

Some places in this file, and also in "src/krux/encryption.py" have typos:

• *_lenght might better be *_length
• *_iteractions might better be *_iterations

This has been very helpful, thank you for this. It's helping me better understand src/krux/encryption.py.

Thank you @jdlcdl for your precious contributions to make Krux better!