[FEATURE REQUEST] - linux commandline decryptor

[slartibart70]

Is your feature request related to a problem? Please describe.
It would be nice to have an additional decrypt-commandline tool so that we can decrypt files not only using the android app but also on other (linux-based) systems
Openssl does support chacha, maybe a script to extract the metadata from the file header (iv, others) would suffice if we can delegate the decrypting work to openssl?
(like openssl enc -d -chacha20 -in ciphertext.bin -out decrypted.txt -K $(cat key.txt) -iv $(cat nonce.txt) -nopad)

Describe the solution you'd like

• copy files from android filesystem to linux
• run decryptor (e.g. in a bash-shell loop) for each file
• enjoy the 'backup' solution in case the android app is not available?

Additional context

[slartibart70]

i think we can directly close this issue: gpts are more powerful than expected :-D

So, this is quickly hacked together:

import struct
import json
from Crypto.Cipher import ChaCha20
from Crypto.Protocol.KDF import PBKDF2
from Crypto.Hash import SHA512

def decrypt_valv_file(file_path, password, output_data_path, output_json_path):
    with open(file_path, 'rb') as f:
        # --- Read metadata ---
        version = struct.unpack('>I', f.read(4))[0]  # 4 bytes, big endian
        salt = f.read(16)                            # 16 bytes salt
        iv = f.read(12)                              # 12 bytes IV
        iterations = struct.unpack('>I', f.read(4))[0]  # 4 bytes iterations
        check = f.read(12)                           # 12 bytes check

        # --- Derive key ---
        key = PBKDF2(password.encode(), salt, dkLen=32, count=iterations, hmac_hash_module=SHA512)

        # --- Read encrypted data ---
        encrypted_data = f.read()

        # --- Set up cipher ---
        cipher = ChaCha20.new(key=key, nonce=iv)
        decrypted = cipher.decrypt(encrypted_data)

        # --- Validate check ---
        decrypted_check = decrypted[:12]
        if decrypted_check != check:
            raise ValueError("Invalid password or corrupted file: check bytes do not match.")

        # --- Read JSON object ---
        data = decrypted[12:]
        if data[0] != 0x0A:
            raise ValueError("Expected newline after check bytes.")
        
        data = data[1:]  # Skip the newline

        json_end_index = data.find(b'\x0A')
        if json_end_index == -1:
            raise ValueError("Could not find end of JSON metadata.")

        json_bytes = data[:json_end_index]
        file_bytes = data[json_end_index + 1:]

        # --- Save outputs ---
        with open(output_json_path, 'w') as json_out:
            json_out.write(json_bytes.decode('utf-8'))

        with open(output_data_path, 'wb') as file_out:
            file_out.write(file_bytes)

        print(f"Decryption successful. JSON metadata saved to {output_json_path}, file data saved to {output_data_path}.")

# Example usage:
# decrypt_valv_file('encrypted.valv', 'yourpassword', 'output.bin', 'metadata.json')

if __name__ == "__main__":
    import argparse

    parser = argparse.ArgumentParser(description="Decrypt Android VALV file")
    parser.add_argument('-i', '--input', required=True, help='Input encrypted file')
    parser.add_argument('-p', '--password', required=True, help='Decryption password')
    parser.add_argument('-o', '--output', required=True, help='Output file for decrypted data')
    parser.add_argument('-j', '--json', required=True, help='Output file for JSON metadata')

    args = parser.parse_args()

    decrypt_valv_file(args.input, args.password, args.output, args.json)

and works ...

commandline-usage:
python decrypt_valv.py -i encrypted.valv -p yourpassword -o output.bin -j metadata.json

Anything we can improve on?

[hej2010]

Check these issue comments, I think there is a working script there :)
#104

[slartibart70]

thanks for the hint, did not see that when looking at the issues.
Still - feel free to add this python script to the repo so we offer users some quick and dirty single-file decryptor solution?