RPOW - Reusable Proofs of Work

[Hal Finney]

Bear writes:
> I'm wondering how applicable RPOW is.  Generally speaking, all
> the practical applications I can think of for a proof-of-work
> are defeated if proofs-of-work are storable, transferable, or
> reusable.  Once they're storable, tranferable, and reusable,
> aren't we restricted to applications already nailed down by
> digital cash schemes?

Well, there are no digital cash implementations that I am aware of.
I think of RPOWs as a sort of "play money" that might be usable in some
applications that would otherwise use digital cash.  I have some code
to play online games with cryptographic protection, cards and dice,
and I am planning to modify it to let people make bets with RPOWs as
the betting chips.

Another way to think of RPOWs is as an implementation of Nick Szabo's
concept of "bit gold".  These are made of bits but have the rarity and
verifiable costliness of a commodity like gold.  Of course they lack
gold's appeal and attractiveness.  Perhaps they could be better thought
of as "bit copper".

> Why doesn't this scheme give rise to a "POW server" that just
> sits there, generating proofs-of-work in advance of need and
> dispensing them at request?  Or even to a company that sells
> POW's to people who can't be bothered to run their own server?
> And doesn't such a device or service defeat the use of POWs
> for real-time load balancing, traffic control, etc?

It's possible that these things could happen, but that's not necessarily
bad.  After all, if people ever got to where they would buy and sell
RPOWs for money, they could serve in place of ecash.  The main question
is whether there will be any use for them so compelling that people
would buy them.

Hal Finney

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