Re: Whoa, now... (was Re: Digital Cash)

From: gtoal@an-teallach.com (Graham Toal)
Date: Sat, 26 Mar 94 11:57:07 PST
To: cypherpunks@toad.com
Subject: Re: Whoa, now... (was Re: Digital Cash)
Message-ID: <199403262043.UAA03969@an-teallach.com>
MIME-Version: 1.0
Content-Type: text/plain
:From: "James G. Speth" <december@end.end.com>
:In fact, he began this thread by citing someone who was talking about using
:an obscured algorithm to prevent digital cash double spending. (ie. If you
:can't get to the algorithm, you can't cheat the system.) His comments were
:on the dangers of relying on this.
:That's the point. Mikolaj was _never_ referring to cryptographic security.
:He was pointing out how security through obscuring algorithms can never be
:considered reliable.
Oh, well if that's what he meant, we agree completely. I thought he was
saying his el33t hackerdoodz buddies could break the crypto part of ecash.
By the way, the reason I've never discussed the ecash threads on this
group is because it was obvious right from the start that double-spending
makes the schemes unworkable, and that only a central reference authority
could patch the system to make it work, which (in my seldom humble opinion)
entirely negates the point of these schemes.
My suspicion is that anonymous ecash can only be made to work if giving
the tokens to someone else is a destructive operation - the way core
memory (I'm probably one of the few people on this group who've had to
worry about stuff like this :-) ) used to be erased when read.
Except that these days, the destructive read would have to be something
secured by the laws of physics, like say a quantum state being trashed
by virtue of being observed. (The way secure quantum comms works - if
we had something akin to a quantum delay line in a card, maybe that
would work.)
However, the technology to do that sort of stuff is probably centuries off.
G

Graham Toal writes:

> By the way, the reason I've never discussed the ecash threads on this
> group is because it was obvious right from the start that double-spending
> makes the schemes unworkable, and that only a central reference authority
> could patch the system to make it work, which (in my seldom humble opinion)
> entirely negates the point of these schemes.

Nope, not "entirely." Anonymity is still preserved, through the
"blinding" operation, even when a clearinghouse approach is used. That
is, the bank can assure itself that it issued the original note, even
though the note presented to it cannot be correlated to the issued
note.

This is the breakthrough Chaum and others achieved. Anonymity (or
untraceablility by Big Brother and Big Mother) is achieved, which is
the major point of digital money. The possible need for online
clearing is not a fatal flaw.

A good place to read about this is the November 1985 "Communnications
of the ACM" journal, in Chaum's cover article "Transaction Systems to
Make Big Brother Obsolete." (Chaum has updated the article since, and
newer versions can be found in various places.)

--Tim May


-- 
..........................................................................
Timothy C. May         | Crypto Anarchy: encryption, digital money,  
tcmay@netcom.com       | anonymous networks, digital pseudonyms, zero
408-688-5409           | knowledge, reputations, information markets, 
W.A.S.T.E.: Aptos, CA  | black markets, collapse of governments.
Higher Power: 2^859433 | Public Key: PGP and MailSafe available.
"National borders are just speed bumps on the information superhighway."

From: mpd@netcom.com (Mike Duvos)
Date: Sat, 26 Mar 94 16:32:42 PST
To: cypherpunks@toad.com
Subject: Re: Whoa, now... (was Re: Digital Cash)
In-Reply-To: <199403262043.UAA03969@an-teallach.com>
Message-ID: <199403270126.RAA16574@mail.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain
> :From: "James G. Speth" <december@end.end.com>
> :In fact, he began this thread by citing someone who was talking about using
> :an obscured algorithm to prevent digital cash double spending. (ie. If you
> :can't get to the algorithm, you can't cheat the system.) His comments were
> :on the dangers of relying on this.
If I may make a small correction here, I suggested a tamperproof software
module could be used in an offline system to process transactions in a
way which prevented "ANONYMOUS double spending". This is not the same as
preventing double spending, although in a system where reputations
matter, it has a certain deterrent effect.
> :That's the point. Mikolaj was _never_ referring to cryptographic security.
> :He was pointing out how security through obscuring algorithms can never be
> :considered reliable.
Obscuring the operation of an algorithm inside a tamperproof module isn't
security through obscurity any more than obscuring plaintext by
encipherment is security through obscurity.
--
Mike Duvos $ PGP 2.3a Public Key available $
mpd@netcom.com $ via Finger. $

> If I may make a small correction here, I suggested a tamperproof software 
> module could be used in an offline system to process transactions in a 
> way which prevented "ANONYMOUS double spending".  This is not the same as 
> preventing double spending, although in a system where reputations 
> matter, it has a certain deterrent effect.
> 
> > :That's the point.  Mikolaj was _never_ referring to cryptographic security.
> > :He was pointing out how security through obscuring algorithms can never be
> > :considered reliable.
> 
> Obscuring the operation of an algorithm inside a tamperproof module isn't
> security through obscurity any more than obscuring plaintext by
> encipherment is security through obscurity.  

	OK, just to go and match the pattern of mis-understandings in 
this thread, i'd appreciate it if you posted a detailed version of your 
plan (sorry if you've done it before, but the 'd' key and I are old 
friends...oops), as i probably just read the bit that leapt out at me and 
ingnored the rest. Then i'll try to punch a few holes in it... :)

MJH

*       *       Mikolaj J. Habryn
                dichro@tartarus.uwa.edu.au
    *           "Life begins at '040."
                PGP Public key available by finger
    *           "Spaghetti code means job security!"