Earlier quoted context omitted.
You're describing public-key cryptography. Sign a message to prove you know a private key that also authorizes the release of funds. This happens to be exactly the functionality of Bitcoin. It is debatable whether known public-key cryptography systems will survive attack for the amount of time under discussion here. I suspect the hack will be to extract the secret from the brain being resurrected, recover the funds,…
A future in which adequately restoring the running processes of the 100 billion neurons of a partly-deteriorated human brain shorn of its body is less difficult than cracking early 2000s public key cryptography sounds like a future sufficiently unlikely to discount when making future plans...
The comment you're replying to made the same point.