Subject: Re: [Bitcoin-development] CoinShuffle: decentralized CoinJoin without trusted third parties

From: xor <[email-masked]>
Date: Thu, 07 Aug 2014 15:00:11 +0200

On Thursday, August 07, 2014 12:22:31 AM Tim Ruffing wrote:
>  - Decentralization / no third party:
> There is no (trusted or untrusted) third party in a run of the protocol.
> (Still, as in all mixing solutions, users need some way to gather together
> before they can run the protocol. This can be done via a P2P protocol if a
> decentralized solution is desired also for this step.)
[...]
> http://crypsys.mmci.uni-saarland.de/projects/CoinShuffle/ for a technical
> overview. 

I think the description at your website leaves out the truly interesting part:
How do you decentralize this securely?
- How do Alice, Bob, Charlie and Dave communicate, i.e. which network is used 
for communication and how?
- How does Alice know that Bob, Charlie and Dave are not the same person?
(= how do you prevent a Sybil attack?)

Because thats the real problem with mixing it seems - ensuring that your 
mixing partners are actually 100 people and not just 1 attacker. There are 
probably many mixing algorithms which work if you solve that problem, but I 
don't see how you offer a solution for it :(