* bellman: add VerificationError
This adds a distinct VerificationError type to the crate and changes
`verify_proof` to return `Result<(), VerificationError>` rather than
`Result<bool, SynthesisError>`. This is significantly safer, because it avoids
the need to mix pattern-matching logic with boolean logic (the cause of
RUSTSEC-2019-0004).
* Rename VerificationError variants per review comments.
* Add missing Clone impl to VerificationError.
Requires the bundled-prover feature, which enables the
wagyu-zcash-parameters crate and adds around 50 MiB to the overall
binary size. That crate bundles the same Sapling parameter files we
normally obtain from disk, so we constrain them to match the same
hard-coded hashes.
Instead of imposing the requirement that bellman users explicitly
specify an engine for every proving system, we allow the Rust type
system to figure it out for us. An engine is specifically useful in
places where we require defined relationships between several types;
ff::ScalarEngine only has one type, and thus any usage of it can be
trivially replaced by an explicit Scalar type. This is also more
readable :)
Define the spend_hash, output_hash, sprout_hash circuit hashes as constants in the load_parameters function, so we don't have to take them as function arguments.
- The internal Option wrapper was an unnecessary leftover from when this
code was directly inside the prover, where Some(x) represents an
assigned variable.
- CommitmentTreeWitness::from_slice_with_depth is more idiomatic Rust.
WARNING: THIS IS NOT ACTUALLY CONSTANT TIME YET!
The jubjub and bls12_381 crates will replace our constant-time usages,
but we NEED to fix ff_derive because other users will expect it to
implement the Field trait correctly.
The ff_derive, pairing, zcash_primitives::jubjub, and bellman dummy_engine
changes are minimally implemented on top of the existing *_assign()
functions.