Demonstrates the algorithm for decoding message bytes with legacy support

decode_radix_message_with_legacy_support.py

# NB - This is intended as pseudo-code and I haven't added exception handling.
#      The message_bytes is schema less and can be anything, so you should assume any of these decodings can fail.
def decode_full_message_with_legacy_support(transaction_context, message_bytes):
    if message_bytes[0] == 0x00:
        post_header_bytes = message_bytes[1:]
        return decode_message_after_header(transaction_context, "PLAINTEXT", post_header_bytes)
    elif message_bytes[0] == 0x01:
        post_header_bytes = message_bytes[1:]
        return decode_message_after_header(transaction_context, "ENCRYPTED", post_header_bytes)
    elif message_bytes[0] == 0x30: # The message uses the legacy doubly-encoded format
        decoded_post_header_bytes = bytearray.fromhex(message_bytes[2:].decode("utf-8"))
        if message_bytes[1] == 0x30: # Header is "3030" which was x00
            return decode_message_after_header(transaction_context, "PLAINTEXT", decoded_post_header_bytes)
        if message_bytes[1] == 0x31: # Header is "3031" which was x01
            return decode_message_after_header(transaction_context, "ENCRYPTED", decoded_post_header_bytes)
    else:
        raise RuntimeError("message_bytes " + message_bytes + " does not contain a valid first byte")

def decode_message_after_header(transaction_context, message_type, post_header_bytes):
    encryption_scheme = post_header_bytes[0]
    payload = post_header_bytes[1:]
    return {
        "type": message_type,
        "encryption_scheme": encryption_scheme,
        "message": convert_to_message_string(transaction_context, message_type, encryption_scheme, payload)
    }

def convert_to_message_string(transaction_context, message_type, encryption_scheme, payload):
    if message_type == "PLAINTEXT":
        if encryption_scheme == 0x00:
            return payload.decode("utf-8")
        else:
            raise RuntimeError("Invalid")

    elif message_type == "ENCRYPTED":
        if encryption_scheme == 0x00:
            raise RuntimeError("Invalid")
        elif encryption_scheme == 0xff:
            decrypt_with_DH_ADD_EPH_AESGCM256_SCRYPT_000(transaction_context, payload).decode("utf-8")
        else:
            raise RuntimeError("Not supported")

    else:
        raise ValueError("message_type has invalid value: " + message_type)

def decrypt_with_DH_ADD_EPH_AESGCM256_SCRYPT_000(transaction_context, payload):
    # Will read various pub/private keys of transaction_context, and decrypt a payload
    # See https://radixtalk.com/t/how-to-decrypt-an-encrypted-transaction-message-created-by-the-radix-wallet/189
    raise NotImplementedError("Not implemented")

test_message_bytes = bytearray.fromhex("303030303734363537333734"); # Should decrypt to "test"

print(decode_full_message_with_legacy_support(None, test_message_bytes))