Crowdfunding with bitcoin
A crowdfunding app that uses bitcoin's smart contracting functionality to let contributors recover their funds if the fundraiser does not reach its goal
Just click here: https://semaphore.finance/
Just click here: https://semaphore.finance/?fundraiser=sprj13n5y0vnu9ajuaund2nxzphy357m82gk7vumup4mys67ketxlsch8wumn8ghj7mn0wd68yat99e3k7mggacq09
Semaphore gives contributors two ways to give someone money: irreversible and reversible. If you choose irreversible, it sends the money straight to the recipient's bitcoin address and there are no "takebacks" after the money confirms. If you choose reversible, it sends the money to a bitcoin smart contract with two spending paths: one lets the contributor take their money back at any time, the other is a "multisig" path that can only spend the money if the contributor and the recipient both cosign a transaction.
After sending money to this smart contract, the contributor creates a bitcoin transaction that sends the money to the recipient but only if the fundraiser reaches the goal amount. The contributor signs this transaction and publishes their signature, and thus the recipient can only take the money if he gets enough signatures on valid contributions that he reaches his goal. If he tries to spend the money in any transaction that doesn't reach the goal, the signatures simply won't be valid, and bitcoin won't let him take the money.
It does. In fact, it's had them since day 1. Satoshi put a crowdfunding feature called "anyone_can_pay" directly into the original bitcoin code and several pieces of software over the years used it, including the now-abandoned Lighthouse project by Mike Hearn. Semaphore is basically just a recreation of that project but now using modern bitcoin tools like taproot.
Well, they're only semi-automatic. When a contributor makes their pledge I also have them create a "recovery" signature that sends their money back to themselves. But this signature is "timelocked" -- another bitcoin smart contracting tool -- so that a transaction that uses this signature is only valid if it is broadcasted after the fundraiser is over. The contributor uploads this signature along with the signature that lets the intended recipient take the money if the goal is reached. If the fundraiser ends and the recipient hasn't taken the money, that signals that the goal was not reached, so a script will automatically recreate the "recovery transaction" and slap on the contributor's recovery signature to make the transaction valid, then "automatically" broadcast it. But I put "automatically" in quotes because it's not fully automatic. Someone has to visit the webpage 24 hours after the fundraiser ends in order to trigger the "automatic" recovery transaction that gives all the contributors their money back. Alternatively, any of the contributors can visit the page themselves and take their money back manually.
Alternative fundraising platforms like geyser.fund don't let contributors take their money back. Contributors send their money directly to the recipient and that's that. I wanted modern "refund" features like platforms like gofundme have, so that's what I made. And all my software is free and open source so companies like geyser are free to use it if they like it.
If you have enough to make up the difference just contribute your own funds to the fundraiser so that you do have enough. That's perfectly acceptable in my opinion and I hope it is clear to contributors that the recipient can contribute too.
The core idea is the same, but:
- To get utxo data, Lighthouse used a p2p network bootstrapped via Mike Hearn's bitcoinXT software. I just use https://mempool.space which is a more centralized way to do it
- Lighthouse assumed users keep funds in the built in wallet and then it marked some of them as "do not spend" if they were designated for a pledge. I just have users send the exact amount they want to contribute and don't assume users keep any additional funds in Semaphore
- I use a multisig so that other people can't "complete" the fundraiser on the recipients behalf, he has to do it himself. I don't think Lighthouse did that, I think it allowed anyone who saw the published signatures to complete the transaction on the fundraiser's behalf
- I have pledgers create 900 signatures in increments of 1% above the goal amount, that way the recipient can take the money even if he 10x's his goal. I don't think Lighthouse did that
- I made a mechanism for semi automatic refunds using (again) presigned transactions, where anyone visiting the site 24 hours after the fundraiser ends automatically sends everyone their money back. I don't think Lighthouse had a similar feature
- I also have an "irreversible pledge" option where you send the money directly to the recipient without doing any funky signature stuff, and I don't think Lighthouse had that