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, and toss the brain in the trash.
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...
It's pretty unlikely that any particular system like Bitcoin will still be around in 100 years. It would be difficult to think of any investment that will still be worth something in 100 years. Buried gold perhaps?
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, and toss the brain in the trash.