On Wed, Aug 07, 2019 at 08:48:06AM -0500, Bryan Bishop via bitcoin-dev wrote:
> Single-use seals
> ================
> This proposal may have inadvertedly demonstrated a practical way to implement
> Peter Todd's single-use seals concept [4]. I am hesitant to say so, though,
> because I think he would ask for a more sophisticated way to verify seal
> closure.

I'm not sure what you're getting at here; single-use-seals are really boring
and simple. To recap, they're akin to a pubkey that has the "magical" property
that it can only be signed once. This of course is impossible with math alone,
but can be implemented with beyond-math mechanisms like trust or PoW (physics).

Thus you have a globally unique seal, which can be closed over a message,
producing a witness attesting to the fact that the seal was closed over that
message. A single-use-seal protocol is secure if it is impossible (in your
chosen security model) to trick the validation function into thinking a single
seal was closed over two different messages.

The obvious implementation with Bitcoin is to define the seal to be a specified
txout, and the witness to be a transaction (and lite client proof) that spends
that txout in a transation with an OP_RETURN output committing to the hash of
the message as the first output. A fancier implementation could use a
pay-to-pubkey-style commitment (RGB¹ uses something along these lines).

For applications requiring a chain of single-use-seals, you can easily keep two
txouts for seals in your wallet, and alternate them as the chain is extended.

Do you mean to say there didn't previously exist a practical way to implement
them? Or that you've found another way? I'm curious what you mean here.

1) https://github.com/rgb-org/spec

https://petertodd.org 'peter'[:-1]@petertodd.org

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