Idea for zero confirmations transactions using “proof of risk”


I was wondering if the following could be implemented on Bitcoin or other cryptos, or maybe in the future with additional opcodes.

Suppose Alice wants to send small transactions to others, without the lightning network (because the recipients might not support it). She puts 5 BTC in a special transaction with the following logic:

  1. After 1 month, the funds go back to Alice
  2. Given a list of UTXOs (that Alice controls), if the top of the stack contains two different signatures of the same UTXO, the 5 BTC can go immediately to anyone (and will probably go to the miner).

Now Alice meets Bob to buy some product and sends him a low-fee 0.01 BTC transaction that may take hours or even days to be added to the Blockchain, from one of the UTXOs in the last list. Bob publishes the transaction to all the miners, and they will confirm that the transaction is “insured” by 5 BTC. They may even offer a bounty to anyone that gives them another transaction from the same UTXO.

Bob can let Alice leave with the product, knowing that if she tries to double-spend the 0.1 BTC, she’s risking a loss of 5 BTC. Bob won’t earn anything if Alice decides to do so, but he can assume that she is rational.

One problem could be that Alice is a miner herself, and might try to mine the double-spending transaction herself (without publishing that second transaction to the other miners). We could solve this by saying that the 5 BTC transaction won’t go to the miner that mined it, but to whoever mines the later 100th block. Alice must be a really big miner if she can take the risk that she will also successfully mine that 100th block.

What do you think?

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