pczt-interop (proof of concept)

A small, runnable proof of concept for cross-implementation interoperability testing of PCZT (Partially Created Zcash Transactions). PCZT is the format that lets one tool build a Zcash transaction, another sign it, and another finalize it. It is the basis for hardware wallets, multisig, and air-gapped signing.

Several teams now implement PCZT independently (OneKey, Ledger, Hito, Keystone, and the reference implementation in librustzcash), but there is no shared way to confirm they interoperate: the pczt crate has a single end-to-end test where librustzcash plays every role at once, and zcash-test-vectors contains no PCZT vectors.

This repo is the seed of a fuller test suite (proposed as a Zcash Community Grant). It demonstrates the approach on real code.

What it does

Running it (cargo run) does four things:

1. Creator role. Builds a base PCZT (v5 transaction, no spends or outputs) with the pczt crate's Creator.
2. Round-trip check. Serializes the PCZT, parses it back, and serializes again, asserting the bytes are identical. Byte-stable serialization is the core property every implementation must agree on to interoperate.
3. Combiner role (a role boundary). Two separate parties each hold the base PCZT, and the Combiner role merges them into one. This is the seed of the full "create on A, sign on B, finalize on C" harness.
4. Test vector. Writes a canonical vector (vectors/empty_v5.pczt plus a JSON manifest with hex and metadata) of the kind that would be contributed to zcash-test-vectors.

Run it

cargo run

Expected output ends with the inspector summary, a successful combine, and the written vector files. Example:

[1] round-trip OK: 101 bytes, byte-stable
[2] inspector
    tx_version          : 5
    ...
[3] combiner OK: merged two parties' PCZTs into 101 bytes
[4] wrote vectors/empty_v5.pczt and vectors/empty_v5.json

Test it

cargo test

Covers byte-stable round-trip, the Combiner merge, and rejection of non-PCZT input.

Scope and honesty

This is a proof of concept, not the finished suite. It uses empty (anchor-zero) bundles so it builds and runs without proving keys or a node. The fuller grant work adds: vectors for real transparent, Sapling, and Orchard cases; a PcztRole adapter trait so independent implementations can be tested against each other (including sign-only hardware devices via exported PCZT files); and per-role diagnostics. See the grant application for milestones.

License

MIT OR Apache-2.0.