fix(zcash): use S.2 transparent_sig_digest for Orchard sighash in shield txs#247
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ZIP-244 §4.9 requires the S.2 form of the transparent digest when computing
the Orchard sighash for transactions with non-empty transparent inputs (shield
txs). S.2 includes UTXO amounts, scriptPubKeys, and an empty txin_sig_digest;
the T.1 (txid) form omits these.
Previously the firmware computed the T.1 form and verified it against the
sidecar-provided value, then used that digest in the Orchard sighash. This
produced Orchard spend-auth and binding signatures that passed local
BatchValidator checks but were rejected by Zebra ("could not validate orchard
proof") because Zebra uses S.2 when verifying Orchard sigs.
Add zcash_compute_orchard_transparent_sig_digest which:
- Returns T.1 when n_inputs == 0 (deshield / private-send, per §4.10b)
- Returns S.2 with empty txin_sig_digest when n_inputs > 0 (shield tx)
Switch zcash_finalize_transparent_digest to use the new function so both the
firmware verification and the Orchard sighash computation use S.2.
The prior commit included an unrelated clang-format pointer-style change (EthereumSignTx *msg → EthereumSignTx* msg) that breaks CI lint-format. Revert to alpha to keep the PR focused on the Zcash S.2 fix only.
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Problem
Shield transactions (transparent input → Orchard output) broadcast with "could not validate orchard proof" from Zebra. Orchard spend-auth and binding signatures were being rejected by the network.
Root Cause
ZIP-244 §4.9 defines two forms of the transparent digest:
prevouts || sequences || outputshash_type || prevouts || amounts || scripts || sequences || outputs || empty_txin_hashThe firmware was computing T.1 to verify the sidecar-provided transparent_digest, then using T.1 in the Orchard sighash. Zebra verifies Orchard sigs with S.2 for any tx with transparent inputs → signatures invalid at the network.
Fix
Add
zcash_compute_orchard_transparent_sig_digest:n_inputs == 0→ delegates to T.1 (deshield / private-send, per §4.10b)n_inputs > 0→ computes S.2:BLAKE2b("ZTxIdTranspaHash", 0x01 || prevouts || amounts || scripts || sequences || outputs || BLAKE2b("Zcash___TxInHash", ""))Switch
zcash_finalize_transparent_digestto use the new function so firmware verifies and signs with the same form Zebra uses.Files
lib/firmware/zcash.c— newzcash_compute_orchard_transparent_sig_digestfunctioninclude/keepkey/firmware/zcash.h— declarationlib/firmware/fsm_msg_zcash.h—zcash_finalize_transparent_digestuses new functionlib/firmware/ethereum_contracts/zxappliquid.c— clang-format cleanup frommake formatTest Plan