whatsapp_web_decrypt_init.py

#!/usr/bin/env python
#coding=utf-8

# Decrypt sent and received WebSocket messages from WhatsApp Web
# To use this version, you need to get data before QR code generation (less convenient than the other script whatsapp_web_decrypt_encrypt.py)
# Only works with Python 2 (you need to install missing packages with a command like python2 -m pip install packagename)
# Remember when sharing scripts / hacks or findings: "the quieter you become, the more you are able to hear"

# https://i.blackhat.com/USA-19/Wednesday/us-19-Zaikin-Reverse-Engineering-WhatsApp-Encryption-For-Chat-Manipulation-And-More.pdf
# https://github.com/romanzaikin/BurpExtension-WhatsApp-Decryption-CheckPoint
# https://stackoverflow.com/questions/66905708/how-to-decrypt-sent-binary-message-by-whatsapp-web/67226952
# Dependencies: https://github.com/sigalor/whatsapp-web-reveng/tree/master/backend

import base64
import curve25519
import hmac
import hashlib
from Crypto.Cipher import AES
from whatsapp_binary_reader import whatsappReadBinary

# JSON key "secret" found with the WebSocket inspector in the network monitor of a web browser after QR code scan
qr_code_secret = "XXX"
# found with a breakpoint on the line "keyPair: t" (without quotes) in the file bootstrap_qr.*.js and a watcher "new Uint8Array(t.privKey)" (without quotes)
priv_key_list = [X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X]
# found with a breakpoint on the line "keyPair: t" (without quotes) in the file bootstrap_qr.*.js and a watcher "new Uint8Array(t.pubKey)" (without quotes)
pub_key_list = [X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X,X]
# Replace with a WebSocket message copied using a tool like mitmdump from mitmproxy (copying the message with the WebSocket inspector in the network monitor of a web browser like Firefox will fail)
message = b'XXX'

def hmac_sha256(key, sign):
    return hmac.new(key, sign, hashlib.sha256).digest()

def HKDF(key, length, app_info=""):
    key = hmac_sha256("\0" * 32, key)
    key_stream = ""
    key_block = ""
    block_index = 1
    while len(key_stream) < length:
        key_block = hmac.new(key, msg=key_block + app_info + chr(block_index), digestmod=hashlib.sha256).digest()
        block_index += 1
        key_stream += key_block
    return key_stream[:length]

def aes_decrypt(key, ciphertext):
    iv = ciphertext[:AES.block_size]
    cipher = AES.new(key, AES.MODE_CBC, iv)
    plaintext = cipher.decrypt(ciphertext[AES.block_size:])
    return aes_unpad(plaintext)

def aes_unpad(s):
    return s[:-ord(s[len(s) - 1:])]

secret = base64.b64decode(qr_code_secret)

private_key = curve25519.Private("".join([chr(x) for x in priv_key_list]))

public_key = private_key.get_public()

assert (public_key.serialize() == "".join([chr(x) for x in pub_key_list]))

shared_secret = private_key.get_shared_key(curve25519.Public(secret[:32]), lambda key: key)
shared_secret_ex = HKDF(shared_secret, 80)
check_hmac = hmac_sha256(shared_secret_ex[32:64], secret[:32] + secret[64:])
if check_hmac != secret[32:64]:
    raise ValueError("hmac mismatch")
key_decrypted = aes_decrypt(shared_secret_ex[:32], shared_secret_ex[64:] + secret[64:])
aes_key = key_decrypted[:32]
mac_key = key_decrypted[32:64]

message_parts = message.split(",", 1)
content = message_parts[1]

decrypted_content = aes_decrypt(aes_key, content[32:])

processedData = whatsappReadBinary(decrypted_content, True)
print(processedData)