KIP-24: Transaction Version 1: New Fields and Hashing

[biryukovmaxim]

KIP-24: Transaction Version 1: New Fields and Hashing

Specifies version 1 transactions: the new fields they carry and how all three transaction hashing contexts treat them.

Scope

New v1 fields (vs v0):

• per-input compute budget (u16) replacing the v0 sig-op count (u8) as the input's committed resource budget;
• optional per-output covenant binding (authorizing_input, covenant_id);
• non-native user-lane subnetworks (and their gas), which v0 transactions may not use.

New v1 txid hashing:

• txid_v1 = TransactionV1Id(payload_digest || rest_digest) using keyed BLAKE3, hashing the payload independently from the rest of the body so ZK/L2 provers can address (or skip) the payload without the full transaction.

How each hash context treats the fields: the KIP states, field by field, how the txid (identity), tx::hash (block-level commitment), and sighash (what a spender signs) handle the new v1 fields, with an explicit v0/v1 commitment matrix.

Design highlights

• Resource commitments (mass, compute budget) are kept out of transaction identity and, for v1, out of the sighash, so miners/relayers can fill or adjust them before mining without invalidating txids or signatures (the deliberate fix from v0, where the sig-op count was committed in the sighash).
• Covenant bindings, being part of what an output is, are committed by all three contexts.
• The hash-function choice (BLAKE3) is presented as a two-domain tradeoff: native execution (where BLAKE3 wins and dominates ecosystem cost) vs ZK-guest execution (where RISC0's SHA-256 precompile wins). The payload/rest split keeps in-guest hashing small, and the v1 txid plus the KIP-21 sequencing-commitment hashers are all BLAKE3, so a prover's full flow avoids BLAKE2b. The choice is explicitly conditional and documented as such.

Status

Implemented in rusty-kaspa across PRs #835 (covenant fields), #849 (v1 txid), #884 (compute budget), and #943 (KIP-21 user-lane subnetworks). Verified against the current implementation in consensus/core/src/hashing/{tx,sighash}.rs, consensus/core/src/tx.rs, and the transaction validator.

References

• KIP-15 — canonical transaction ordering and sequencing commitments
• KIP-20 — covenant IDs
• KIP-21 — partitioned sequencing commitment, lanes, gas, subnetwork namespace