[closed] Wanted: About 1.5-2.5 ZEC for Paypal USD

General
10

This offer is still open (though maybe for different amounts, around 1-1.5 ZEC on below terms). It became a sort of mini research project for me: How to create trust, with asymmetry in risks between Paypal and cryptocurrency. TL;DR: I must risk cryptocurrency I already have, and a substantial time of locked-up funds on 2/2 multisig. See below for idea.

@Autotunafish, thanks for the kind words. I wish that nobody abused anonymity. I also wish that nobody abused knives, axes, hammers, chainsaws, automobiles, alcoholic beverages, etc. I also wish that I lived in a community where nobody locks doors at night.

Too bad, the Internet is not that community. Though I would like to think that Zcash forums are a place where I can take the below-described risk on someone with a solid posting history.

Stay skeptical, stay safe!

With that in mind, for somebody who has Zcash to sell…

After a week exploring script options, realizing that weird scripts should be tried on testnet not with real money, realizing and then trying to prove the futility of what I was trying to do… This is the best/simplest I came up with, for aligning incentives:

  • ZEC funds held in 2/2 multisig for n days. Max n I can accept is n=30. I know theoretically, Paypal can be reversed longer than that. But I can’t afford to leave funds locked up, at my risk for longer; and your biggest risk is if it is a hacked/stolen Paypal. There is a very high probability of Paypal owner discovering a few hundred dollars missing within 30 days! I think only the real Paypal owner will make such a deal, because also:

  • I risk ZEC up-front, in same multisig. I only get my original ZEC back (plus the amount I bought) if we both perform the transaction honestly. I think no scammer will risk cryptocurrency they already have, with a very high chance for the scam to be caught within 30 days.

I have already moved ZEC funds to t-addr t1LhRiXxZynq1R2iBXorqHZuqzrb7DqjtKS for this purpose, to show I’m serious and I have the funds. (I put slightly more, to cover tx fees; I will send to the multisig 1.0001 ZEC minus whatever fee zcashd calculates.) Proof that this is my address and my money:

user@host:~$ zcash-cli signmessage t1LhRiXxZynq1R2iBXorqHZuqzrb7DqjtKS \
  "I, @uid65534 on forum.zcashcommunity.com, own t1LhRiXxZynq1R2iBXorqHZuqzrb7DqjtKS."
IGUZOJBMlpsp6uKZm7LKKBi15UH/j2xMVFy/OWh7bV9QQWs4smSwPSyY1mqRq6rdRND4Bzo2i5X2RlzSZTvfFqE=
user@host:~$ zcash-cli verifymessage t1LhRiXxZynq1R2iBXorqHZuqzrb7DqjtKS \
  IGUZOJBMlpsp6uKZm7LKKBi15UH/j2xMVFy/OWh7bV9QQWs4smSwPSyY1mqRq6rdRND4Bzo2i5X2RlzSZTvfFqE= \
  "I, @uid65534 on forum.zcashcommunity.com, own t1LhRiXxZynq1R2iBXorqHZuqzrb7DqjtKS."
true

(Newbies, copy/paste the second part (verifymessage) to verify the message on your own computer. You will not be able to do the first part, because you don’t have my private key.)

Proposed concrete protocol, where you = seller and I = me:

  1. We agree privately on price and terms.

  2. You tell me a t-address for yourself. I create a 2/2 multisig address, and publish all three addresses on this thread: The multisig t-addr, your signing t-addr, my signing t-addr. If you want to verify the redeemScript for the multisig, I will send that to you privately.

  3. I send agreed USD via Paypal, and I send (slightly more than) 1.0 ZEC to the multisig address. At this point, my total risk is $[agreed USD] plus 1 ZEC.

  4. After you receive Paypal tx and verify that I sent 1 ZEC from t1LhRiXxZynq1R2iBXorqHZuqzrb7DqjtKS to the multisig, you send the agreed ZEC to the multisig.

  5. 30 days from initial tx date (I hope today), if no reversal of Paypal, you release your part of the multisig. I get all my ZEC (both the ZEC you sold me, and the ZEC I put up-front). We update this forum thread.

In case there is a big market swing, or I find a better deal, I may cancel this offer at any time before I reach a firm agreement with somebody (step 1 above).

Design notes:

  • I think most game-theoretic constructions are naive. They assume people are rational. But people are not rational! I designed this so I can only cheat if I am extremely irrational: So malicious I will spend large sum to cause trouble for some random stranger, with no material benefit to myself (only loss). The risk is shifted too much: My counterparty can cheat if only moderately irrational. But I am willing to take that risk, iff counterparty has what I consider a good reputation.

  • Here, my biggest risk is that my counterparty could hold ZEC hostage: Demand I sign to release part of the amount to me, part to him/her, instead of all to me. This is the gaping hole in most such protocols. But I should state upfront, I am one of those principled people. I would burn all my ZEC and die in a gutter before negotiating with a scammer. This is a personality characteristic. People call me words like “stubborn”, “obstinate”, “rigid”, sometimes “stupid”. If I perform my part honestly, and the seller gets my USD, then I promise I will never release my part of the multisig for anything but the full amount to me.

Any takers? This past week, there have been people complaining that “there are zero buyers around”. I am ready to buy! Current price where I sit is $232.838/ZEC.

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