[Cryptography] Electronic currency revived after 20-year hiatus

[Allen]

>
> Note that Bitcoin - specifically proof-of-work - does solve a problem that
> signature-based approaches can't: even if the people building consensus in
> Bitcoin (miners) all conspire to change history, it's provably expensive
> for
> them to rewrite history because they have to re-do all the proof-of-work.
> That's not true in signature based consensus, as forging a signature is
> free.
>

Not so easy though if all honest participants use a signing key only once,
publishing a new public signing key and overwriting the old private key
each time they sign a block.  Once the old private key is overwritten, it's
impossible to revise the history (except to rewrite it completely by
changing the software to accept a different genesis block, which I think
would be possible with any blockchain).
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