Secure signatures without a private key

This is a neat hack. I think the effect is that it makes the signature equivalent in security to a cryptographic digest, in that anyone can recalculate a matching digest from the same file. Rather different from the usual purpose of a public key signature, which is to authenticate the creator using a public key that is known beforehand, and linked to the creator via some kind of PKI. The neat hack works when an artefact can state its own public key with “trust me, bro” authentication, in which situation I wonder why there’s a signature (instead of just a digest) in the first place.

Nice. I believe this is essentially the same trick used in Nick's Method (https://medium.com/patronum-labs/nicks-method-ethereum-keyless-execution-168a6659479c). It can be used to create an Ethereum transaction that is not signed with an existing private-key: a transaction is created but not broadcast; the v, r, and s fields are manually modified; then the corresponding public-key is recovered and funded; and then the transaction is broadcast. It has applications such as deploying a smart contract to multiple chains at the same address.