aesgcm/aesgcm_decrypt.py

import argparse
import urllib.request
from Crypto.Cipher import AES
from os import remove

DESCRIPTION = f"{__file__} - decrypt AES-256-GCM URL"

def read_file(file_path: str):
    try:
        file = open(file_path, "rb+")
        return file.read()
    except FileNotFoundError:
        print("File not found")

def write_file(file_path: str, data):
    try:
        file = open(file_path, "wb+")
        file.write(data)
    except Exception:
        print(f"Cannot write file: {file_path}")

def encrypt(key, data):
    cipher = AES.new(key, AES.MODE_GCM)
    encrypted = cipher.encrypt(data)
    return encrypted, cipher.nonce

def decrypt(key, iv, data):
    cipher = AES.new(key, AES.MODE_GCM, nonce=iv)
    decrypted = cipher.decrypt(data)
    return decrypted

def main():
    parser = argparse.ArgumentParser(description=DESCRIPTION)
    parser.add_argument("url", help="URL with file to decrypt, e.g. aesgcm://download.montague.tld/4a771ac1-f0b2-4a4a-9700-f2a26fa2bb67/tr%C3%A8s%20cool.jpg#8c3d050e9386ec173861778f68e9af38a97aaf82faa4063b4d0878a61261534410c8a84331eaac851759f587")
    args = parser.parse_args()

    splited_url = args.url.split("#")
    download_url = splited_url[0]
    download_url = download_url.replace('aesgcm://', 'https://')
    splited_download_url = download_url.split('/')
    file_name = splited_download_url[len(splited_download_url) - 1]
    file_name_enc = f'{file_name}.enc'

    # print(f'Downloading {download_url} to {file_name_enc}')
    urllib.request.urlretrieve(download_url, file_name_enc)

    iv_key = splited_url[1]
    iv = iv_key[:24]
    key = iv_key[24:]

    encrypted_data = read_file(file_name_enc)
    iv_b = bytearray.fromhex(iv)
    key_b = bytearray.fromhex(key)

    decrypted = decrypt(key_b, iv_b, encrypted_data)
    write_file(file_name, decrypted)
    remove(file_name_enc)
    print(file_name)

if __name__ == "__main__":
    main()