From: jamesd@echeque.com
Date: Mon, 1 Apr 1996 19:45:23 +0800
To: Chein-hsinLiu <cypherpunks@toad.com
Subject: Re: Question about integrity of Blind Signature
Message-ID: <199604010615.WAA05677@mail1.best.com>
MIME-Version: 1.0
Content-Type: text/plain


At 11:51 PM 3/31/96 +0800, Chein-hsinLiu wrote:
>  Hi!
>I have some question about ecash protocol. In ecash protocol, we represent
>money by a sequence number which is signed by bank. And for privacy, we
>use blind signature. But when we send bank a pesudo sequence number--
>X*PK(r) (X:sequence number we want, r :random number to cheat bank)
>then we can get SK(X*PK(r)) from bank, and get money by SK(X*PK(r))/r=SK(X).
>But if we divide SK(X*PK(r)) with r', we can get another money? It confuses
>me. How does it preserve the integrity of the money, and let people divide
>r on the SK(X*PK(r)) ?

The sequence number is not a sequence number, nor is 
it just any random number.  It is a random number of 
some special form, so that the chance that the "other money" 
will be of this special form is remote.  For example one 
might demand that every second hex digit was the number 7, 
and the other digits were random.  When we divide a valid 
money number by r, we will not get another valid money number.



>  It confuses me very long time. Thanks for any help!
>  Chein-hsin Liu 4/1/96
>
>
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