Subject: Re: [bitcoin-dev] Improving JoinMarket's resistance to sybil attacks using fidelity bonds

From: Dmitry Petukhov <[email-masked]>
Date: Fri, 26 Jul 2019 14:38:38 +0500

В Fri, 26 Jul 2019 10:10:15 +0200
Tamas Blummer via bitcoin-dev <[email-masked]>
wrote:

> Imposing opportunity costs however requires larger time locked
> amounts than burning and the user might not have sufficient funds to
> do so. This is however not a restriction but an opportunity that can
> give rise to an additional market of locking UTXOs in exchange of a
> payment.
> 
> This would give rise to a transparent interest rate market for
> Bitcoin an additional huge benefit.

Wouldn't that 'locked utxo rent' market just drive the cost of attack
down to manageable levels for the attacker ?

The owner of the locked utxo can derive potential profit from it by
being a maker, and then the profit will be reduced by operational
expenses of running a maker operation.

The owner of utxo can just 'outsource' that task to someone, and pay
some fee for the convenience.

In effect, the owner would be renting out that utxo for the price of

<maker_profit> - <operational_expenses> - <convenience_fee>

If the attacker is the entity who provides this 'maker outsourcing',
and it captures significant portion of that maker-outsourcing/utxo-rent
market, it can even receive some profit from the convenience fee, while
deanonymizing the joins.

And with pseudonymous entities, you cannot be sure how much of that
market the attacker controls.