Date: Wed, 07 Aug 2019 11:20:38 +0000
To: Chris Belcher <belcher@riseup.net>
From: ZmnSCPxj <ZmnSCPxj@protonmail.com>
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Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Improving JoinMarket's resistance to sybil
	attacks using fidelity bonds
Precedence: list

Good morning Chris,

> Also, as described in my other email
> (https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2019-August/0172=
18.html
> starting "
> Let's say the sybil attacker...") the superlinear V^2 term is essential
> to the resistance of the fidelity bond system to sybil attacks.

At the cost of *greatly* strengthening aggregation.

Suppose there is currently many makers, all with roughly-equal bonds.
Suppose I were to approach two of these makers, and offer to aggregate thei=
r bonds.
The combined bond would, because of the V^2 term, have 4 times the weight o=
f the other makers.
Thus, approximately I can earn a little below 4 times what one other maker =
does.
I offer 1.5x what one maker does to both of those makers and keep a little =
below 0.5x to myself.
So:

1.  I earn without putting any of my money into bonds.
    I just need starting capital to pre-pay for the rents.
2.  I get to learn a little below 4x more CoinJoins than other makers.
    This increases my earnings further since I can sell this privacy inform=
ation, and I also get an advantage compared to other non-aggregating spies.

It seems to me not to fix the root issue, i.e. makers who make for the purp=
ose of gathering privacy information, even if it might fix sybil attackers.

Regards,
ZmnSCPxj