Over the years while compute power increases we regularly increase key sizes in every application that uses encryption.   How does this work in bitcoin?   Is there a mechanism to handle this?   What about the old private keys that have been used?   Can they be marked expired and recreated with a new larger key size?  Even if so, what about those that don't bother to create new keys?  If someone is eventually able to figure out a private key that was used won't they be able to sign as that key?    I'm really curious what bitcoin's mechanism is to protect against this as compute power increases.   I'm thinking mainly of private keys because it seems like being able to sign as someone else can be really damaging, but the hash algorithms must be accounted for as well?  Being a fiat currency, even a small flaw can destroy the faith in and so the value of the currency, so this seems pretty important.    I know very little about the implementation here, so if anyone could provide insight on how these things work it would be appreciated.