The verifier's check in the inner product argument used to assume that the
G'_0 value had an additional (trivial) blinding factor term, which makes
it slightly easier to reason that it never is the point at infinity.
However, we never sample challenges that are zeroes (both for security
and completeness reasons) so this element would never be the point at
infinity anyway. Thus, we can simplify the check with the added benefit of
matching the book's description of the protocol.
Previously `plonk::verify_proof` took an `MSM` as an argument, to enable
batch verification. However, this also required that it take a source of
randomness in order to enforce separation of proofs within a batch. This
made single-proof verification unnecessarily non-deterministic.
We now have a `VerificationStrategy` trait encapsulating the necessary
details, and separate `SingleVerifier` and `BatchVerifier` structs for
the specific variants. Proof verifiers no longer need to create and
manage the `MSM` themselves, and single-proof verifiers no longer need
to supply a source of randomness.
Co-authored-by: Sean Bowe <sean@electriccoin.co>
Jack Grigg
Sean Bowe