Question About local signing API

I want to use local signing API but i cannot understand.

How can i use local signing API?

I want to put parameters like privatekey,publickey,long ID for "manually", not automatically.

Someone can help with examples?

Follow the constructor nxt.blockchain.ChildTransactionImpl#ChildTransactionImpl which builds and signs a transaction. That constructor takes all the different pieces of the transaction and assigns them to class fields. Then it computes the signature using the private key, i.e. sign the transaction. That happens at line #171:

this.signature = Crypto.sign(bytes(), privateKey);

If you follow the bytes() method you will see how the transaction is converted to a byte array.

What is fxtTransaction?

"fxt" is an internal name (historical reasons) for the parent chain Ardor.

I realize I'm jumping a bit late into this discussion, however there are two simple methods to perform local signing that you should know about:

  1. In the client example classes see class LocalSigning from package com.jelurida.ardor.client.api this is a sample utility class that demonstrates how to use local signing using the APIs without having to mess with internal crypto.

  2. Another simple option if you prefer Javascript is to use the Ardor node JS module which reuses the official code from the wallet for doing local signing, the added bonus is that it also validates that the bytes returned from a remote node indeed corresponds to the json you submitted.