I'm looking at the multisignature scheme provided by MRL005 Section 4.4, and some things are unclear to me. I've attached a picture below of the expression for which I'm seeking some clarification.
Above, we have:
- A generated key image (Ij)
- A hash function (H)
- A shared public key (Pe)
- And a signer-specific public key (Pj)
No ambiguity there.
The actual operations required to calculate a given key image are the core of my questions.
Question 1: For the term (Pe | Pj)
- Am I correct to interpret this as an inner product of the shared, and signer-specific public keys?
Question 2: For the term (Pe | Pj)
- How would one actually calculate this value, given the two public keys? A detailed example would be preferred here.
Question 3: For the term H()
- Which hash function is used here? Sha512, as in EdDSA? Keccak? Or something else?