LGTM but can you explain in the PR (1) what a private hidden key is and (2) how this implementation matches the implementation in the Dart client

Ah my fault, now that I am looking at the Dart client, PrivateKeys in the Dart client are prefixed with privatekey:... my code makes the keys prefixed with _ because I thought privatekeys were the same as internal hidden keys..

Should I just close this or refactor everything to InternalKey ?

Also I've tried to create my own privatekey in my secondary manually and it would not work @gkc any idea why?

@smoothalligator@ update:privatekey:test@smoothalligator fascin
org.atsign.common.AtException: error:AT0016-Invalid key : Key privatekey:test@smoothalligator is invalid
        at org.atsign.client.api.impl.secondaries.RemoteSecondary.executeCommand(RemoteSecondary.java:102)
        at org.atsign.client.api.impl.clients.AtClientImpl.executeCommand(AtClientImpl.java:385)
        at org.atsign.client.cli.REPL.repl(REPL.java:183)
        at org.atsign.client.cli.REPL.main(REPL.java:53)
Calling System.exit

Is it because I am only allowed to read private keys and/or modify pre-existing private keys?

Please set up some time to discuss this with @murali-shris ... it's important we retain consistency on the core concepts across SDKs

at_commons has classes & methods to determine what sort of key type a key is. That is canonical, Java SDK should be exactly aligned

Start by looking at AtKey.getKeyType in at_commons

Thank you @gkc I will close for now because I do not think I did the correct approach.