decrypt.py

import sys
import requests
import base64
import hashlib
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import padding

def decrypt_string(ciphertext, lnurlw):
    key = hashlib.sha256(lnurlw.encode('utf-8')).digest()
    cipher = Cipher(algorithms.AES(key), modes.ECB(), backend=default_backend())
    decryptor = cipher.decryptor()

    decoded_ct = base64.urlsafe_b64decode(ciphertext)

    decrypted_data = decryptor.update(decoded_ct) + decryptor.finalize()

    # Use PKCS#7 unpadding
    unpadder = padding.PKCS7(128).unpadder()
    unpadded_data = unpadder.update(decrypted_data) + unpadder.finalize()

    return unpadded_data.decode('utf-8')


def fetch_json_from_url(url):
    try:
        response = requests.get(url)
        response.raise_for_status()
        return response.json()
    except requests.exceptions.RequestException as e:
        print(f"Error fetching JSON from URL: {e}")
        sys.exit(1)


def main():
    if len(sys.argv) > 1:
        url = sys.argv[1]
        json_data = fetch_json_from_url(url)
    else:
        # Use the provided JSON if no URL is specified
        json_data = {
            "cashu_ciphertext": "QP4A9aOYzP5Rwt6ek-CjFR1yZXQfvRI067Vj0XG8g-XUh6T8zWpCWTWThomG-W1rB_Jq65HEomvIrI_-enwqSl6Ao2rRHyitJMYtzkJrrvygvLLFjA3BgSBQAVxiSHP4MrTSDZa9vLSxlJItHrjFoqV-Wbt_DMGknlbHIsS1s7QWnOyiLl4DOO_VxZJJJPfySwEcGBGMl6fpn1zDZ1OtruEFmlYFFex-i19RYvB78xusXdux7eT-QQN7SHvEUhJmbxNCU_WGOlOMIc-JVWR7PzQVjG_ajq0iP8VQu6Rkfna73LJF6nUiEUjHyKAMQz1_C2wL72i1juwXGur0SKi-5JKv-q7rfm83SbZypwcBMWlo39n1afALESR9NrbE5K35z3JFXwjmYoXELFzGkJ0YhE2jhtyqNubOmZvAfB2IfNyvmwBbTgQ-M01r-lqbjv3LKT7KHxPNAle6iXa-nLwBfg==",
            "cashu_plaintext": "cashuAeyJ0b2tlbiI6IFt7InByb29mcyI6IFt7ImlkIjogIkkyeU4raVJZZmt6VCIsICJhbW91bnQiOiAxLCAic2VjcmV0IjogIjQ2YWQzOTdkM2VmNjA0MzQ1MmE5YTM5MWE4YTM4YjZjZDVkNjAyMTIxNzMzMzYzODY5ZjRhYWM1ZjllMjQwMDgiLCAiQyI6ICIwMjcxMjlmYzEzMTgzMGM0ZjdmZGIwNmE4ZTNmMTNkZmNlNzk0NzU4OTUxM2Y5Y2ZmOTc1Y2MxNjU2NThlNDMxNjUwNjk2NjM5IiwgImMiOiAiMTg2NzI3NmFkYmRlMjIwNGEwNDUyM2EwYTcyYjIzYjZiNzBlN2M5MTFiODc2Y2I4Njg3Njc0YzliYmM1ODUwN2Y2In1dfSwgIm1pbnQiOiAiaHR0cHM6Ly84MzQxLnNwYWNlOjMzMzgvIn0=",
            "encryption_key_full": "LNURL1DP68GURN8GHJ7MR9VAJKUEPWD3HXY6T5WVHXXMMD9AMKJARGV3EXZAE0V9CXJTMKXYHKCMN4WFKZ7DT5WU6HZ4ZXG35K7MJKDG6HX3T4GEGHW4F59AZ52WFHGFX4V6NCGEEX7URTGFX8G6JYD4U42FUGE4K",
            "encryption_key_hint": "LNURL1DP68GURN8GHJ7MR9VAJKUEPWD3HXY6T5WVHXXMMD9AMKJARGV3EXZAE0V9CXJTMKXYHKCMN4WFKZ7DT5WU6HZ4ZXG35K7MJKDG6HX3T4GEGHW4F59AZ52WFHGFX4V6NCGEEX7URTGFX8G6JYD4U42FUGE4",
            "index": 1,
            "key": "6694580efc7d570210393c5ce52c3ff681e6c15ef145e5981502c6129e0ab6b6"
        }

    lnurlw_key = json_data["encryption_key_full"]
    encrypted_message = json_data["cashu_ciphertext"]
    print()
    print("Encrypted message:", encrypted_message)
    print()

    decrypted_message = decrypt_string(encrypted_message, lnurlw_key)
    print("Decrypted cashu note:")
    print()
    print(decrypted_message)
    assert decrypted_message.startswith("cashu"), "Decrypted text does not start with 'cashu'"
    assert decrypted_message == json_data.get("cashu_plaintext")

if __name__ == "__main__":
    main()