What is the key blinding function used in the hidden service protocol v3?

Question

I've read the rend-spec-v3.txt document which is supposed to be the specification for the v3 hidden service protocol. The document makes several references to a key blinding function that takes in an ed25519 key pair/public key and a nonce and gives a new key pair/public key which is used to determine the hidden service's position in the hash ring. In Appendix A1 however, it just describes the scheme but doesn't define a specific function. I know for certain the protocol has been implemented because we've been able to use the new 56 character addresses for a while now. So, is there a specification or document I'm missing? Is the current implementation a placeholder? How exactly does the current protocol handle addresses and find where the descriptors are stored?

P.S. The specification also says there's a new flag "HSDirV3" but it's nowhere to be found in the consensus. Has that flag been discarded?

Answer 1

I've messaged one of the tor developpers and he's been kind enough to answer. In the rend-spec-v3.txt document, the function is actually specified in appendix A2. And the "HSDirV3" flag never existed. It'll be removed from the specification.