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Date: Mon, 2 May 2022 10:23:50 +0100
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To: ZmnSCPxj <ZmnSCPxj@protonmail.com>
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From: Chris Belcher <belcher@riseup.net>
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Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] BIP proposal: Timelocked address fidelity bond
 for BIP39 seeds
Precedence: list

Hello ZmnSCPxj,

Renting out fidelity bonds is an interesting idea. It might happen in 
the situation where a hodler wants to generate yield but doesn't want 
the hassle of running a full node and yield generator. A big downside of 
it is that the yield generator income is random while the rent paid is a 
fixed cost, so there's a chance that the income won't cover the rent.

JoinMarket takers since the start have checked that a fidelity bond 
doesn't appear twice. The technique doesn't deserve a section in the BIP 
because this BIP is only about specifying the wallets that hold fidelity 
bond UTXOs for makers, not takers which receive fidelity bond messages.

In JoinMarket this is done in this code here:
https://github.com/JoinMarket-Org/joinmarket-clientserver/blob/6b05f65260a487cd22f175ba64d499fbe8122530/jmclient/jmclient/taker.py#L1020-L1021

Best,
CB

On 01/05/2022 12:41, ZmnSCPxj wrote:
> Good morning again Chris,
> 
> I wonder if there would be an incentive to *rent* out a fidelity bond, i.e. I am interested in application A, you are interested in application B, and you rent my fidelity bond for application B.
> We can use a pay-for-signature protocol now that Taproot is available, so that the signature for the certificate for your usage of application B can only be completed if I reveal a secret via a signature on another Taproot UTXO that gets me the rent for the fidelity bond.
> 
> I do not know if this would count as "abuse" or just plain "economic sensibility".
> But a time may come where people just offer fidelity bonds for lease without actually caring about the actual applications it is being used *for*.
> If the point is simply to make it costly to show your existence, whether you pay for the fidelity bond by renting it, or by acquiring your own Bitcoins and foregoing the ability to utilize it for some amount of time (which should cost closely to renting the fidelity bond from a provider), should probably not matter economically.
> 
> You mention that JoinMarket clients now check for fidelity bonds not being used across multiple makers, how is this done exactly, and does the technique not deserve a section in this BIP?
> 
> Regards,
> ZmnSCPxj