This message was signed with Hal’s key.. we know someone has control over his key after his death and has used it.

(1) who has Hal’s key

(2) where did Martin “find” this message to be able to decrypt it

There’s obviously some sort of agenda here involving multiple people, it’s just not clear at the moment what this particular agenda is.

Sorry, I was being somewhat sarcastic and it misfired. The only real option is the last one. The key is most likely compromised.

its plausibly debatable

someone who isnt paul le roux left their signature saying it was paul le roux, in case it ends up being read one day