[Lucrative-L] lucrative accounts revisited

[Bill Stewart]

At 04:17 PM 04/24/2003 -0400, R. A. Hettinga wrote:
>You *delete* the spent coins after some pre-arranged period. They're useless.

That only works if you've modified your protocols to identify the ages of 
coins,
for instance by rotating what signature parameters the bank uses.
Otherwise somebody can walk in with a used P+1-old coin and spend it again.

If you do modify the protocols to identify coin or signature batches,
and delete older batches of coins, you have to also refuse to cash them,
like checks that say "Not valid after 90 days" or whatever.
This implies that users will be required to come in and exchange coins
every so often before they expire, or lose their money.
For most markets, this may be ok with appropriate time periods,
but for other applications, it might not be.

One alternative is to keep only the new batches in high-speed storage,
and if somebody comes in with a bunch of dusty old coins,
you say "eh, haven't seen one-a them in a long time,
lets' see what we've got back in the back room",
and go drag out the punch cards and 9-track-tape with the old databases on 
them.
How expensive is this?  Well, the going rate for disks is about $1/GB,
and I forget how big the coins are but they're unlikely to be over 1KB,
so that's about 1 microbuck per coin, plus some labor cost for fetching old 
records,
and a $1000 stack of drives holds a billion spent coins.
CDRs are more trouble to handle, but only cost about $0.25/GB;
I'd expect the write-once DVD market to be similar until blue-ray gets common.