From: Jiri Baum <jirib@cs.monash.edu.au>
Date: Thu, 21 Sep 95 20:14:06 PDT
To: cwe@Csli.Stanford.EDU (Christian Wettergren)
Subject: Re: Exchange random numbers (was: Re: netscape's response)
In-Reply-To: <199509211852.LAA22259@Csli.Stanford.EDU>
Message-ID: <199509220312.NAA15933@molly.cs.monash.edu.au>
MIME-Version: 1.0
Content-Type: text/plain


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Hello stewarts@ix.netcom.com, cypherpunks@toad.com, jsw@netscape.com
  and Christian Wettergren <cwe@Csli.Stanford.EDU>

Christian Wettergren <cwe@Csli.Stanford.EDU> wrote:
...
> | If I only ever give out a hash of my seed, and only ever *add* any received
> | info to my seed (and stir it in well), how can anyone find out anything?
> | (Apart from hash weaknesses.)
> 
> Giving out contribution: 
>      MD5(select_bits(my_seed, start_bit, stop_bit)) -> remote
> Taking in contribution : 
>      my_seed = my_seed XOR 
>      ((select_low_bits(remote_contrib, contrib_width) << contrib_area)

Hmm, I use:
  taking-in:
	seed = MD5(seed,new-data)
  giving-out:
	MD5(seed)

(where every giving-out is preceded by a taking-in). Is that OK?
If not, why not and how can I improve it?

> You also need to keep track of who has contributed what, and how much.
...

Why? I guess to keep track of how much entropy I believe I have...

> This might become a problem if you don't have a safe authentification
> mechanism, like baseing the tracking on the IP-numbers etc.

That's a safe authentication mechanism? I don't think so.
But you need a secrecy mechanism, so I guess that's where you'd
add your auth.

...
> The boot-strap stage is actually the big problem still. But if the
...

The boot-strap is done only once (at install time) so it's not a big
problem to ask for lots of random text from user.

...
> | In any case, accepting donations of entropy cannot possibly reduce the
> | amount of entropy I have, can it?
> 
> This isn't a problem as I see it, he'll only know what bits he
> flipped, not the actual state.

Good, I thought so.

Sorry, have to go now, rest later...

Jiri
- --
<jirib@cs.monash.edu.au>     <jiri@melb.dialix.oz.au>     PGP 463A14D5

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