It is impossible to prove that somebody is Satoshi.
I firmly believe that even if real satoshi turned up one day, people will also declare him Faketoshi.
This is so true.
Even if Satoshi presents his privatekeys, signs messages, shows his passwords, e-mail account accesses... it could be someone else who has all these privatekeys, passwords, accesses now.
He would only prove the ownership of these but it is impossible for somebody to prove that he is Satoshi.
It is possible all of the proof that he would show is legit so why would we doubt him?
If that person could open up all the old e-mails or Satoshi's account+private keys then why should we doubt him?
But this scenario seem's impossible to happen after all Satoshi vanish wothout a trace so that mean's he doesn't have a plan to reveal his true identity.
that is correct , but op seems keep doubting even with all those legitimate proof.
which means this discussion will never ending lol . too much -if- in his thoughts like :
what if the privkey has changed hands for reasons
what if all those sign messages, email account was hacked etc
what if op has been convinced finally but he got a brain ill that makes all of these discussions useless haha -no offense please-
it should not be easy for someone to somehow steal/hack satoshi credentials while satoshi himself invented the world best financial security system called bitcoin. he must have the best way to keep his credentials privkey secured.
this is a perspectives game , for me and for most people around here the privkey and sign message of the genesis block is more than enough. end of story. if you feel still doubtful well good luck.