New Release 4.5.1

TL;DR: This is a required update for all testnet nodes, and is highly recommended for mainnet nodes if you are using the getbalance RPC method.

Testnet Orchard Circuit Changes

In the zcashd 4.5.0 blog post, we indicated that a testnet rollback might occur to update the consensus rules, if we needed to make backwards-incompatible changes. Shortly after zcashd v4.5.0 was released, during another internal review of the Orchard circuit, we identified two bugs that would affect the upcoming testnet activation of NU5:

• The diversifier base g_d_old, for the note being spent, is required to be a non-identity point. A note created from a payment address with g_d set to the identity (via collaboration between sender and recipient) could be spent multiple times with different nullifiers (corresponding to different ivks). The code outside the circuit correctly enforced the non-identity requirement, but the circuit did not correctly constrain this, and allowed the prover to witness the identity.
• SinsemillaCommit can be modeled as a Pedersen commitment to an output of SinsemillaHash: SinsemillaCommit(r, M) = SinsemillaHashToPoint(M) + [r] R. The specification used incomplete addition here, matching its use inside SinsemillaHash. However, unlike in SinsemillaHash, an exceptional case can be produced here when r = 0. The derivations of rivk (for computing ivk) and rcm (for computing the note commitment) normally ensure that r = 0 can only occur with negligible probability, but these derivations are not checked by the circuit for efficiency; thus SinsemillaCommit needs to use complete addition.

These bugs do not affect mainnet, as zcashd v4.5.0 only set the activation height for NU5 on testnet for testing purposes. Nevertheless, in the interest of keeping the testnet environment as close to mainnet as possible, we are fixing these bugs immediately. This means a change to the NU5 consensus rules, and a new testnet activation height for NU5.

To this end, the following changes are made in zcashd v4.5.1:

• The consensus branch ID for NU5 is changed to 0x37519621.
• The protocol version indicating NU5-aware testnet nodes is set to 170015.
• The testnet activation height for NU5 is set to 1,599,200.

Testnet nodes that upgrade to zcashd v4.5.1 prior to block height 1,590,000 will follow the new testnet network upgrade. Testnet nodes that are running zcashd v4.5.0 at that height will need to upgrade to v4.5.1 and then run with -reindex.

Fixed regression in getbalance RPC method

This release also fixes a regression in the getbalance RPC method. zcashd v4.5.0 removed the account API from the wallet, following its deprecation and removal in upstream Bitcoin Core. As part of the upstream changes, the getbalance RPC method was altered from using two custom balance computation methods, to instead relying on CWallet::GetBalance. This method internally relies on CWalletTx::IsFromMe as part of identifying “trusted” zero-confirmation transactions to include in the balance calculation.

There is an equivalent and closely-named CWallet::IsFromMe method, which is used throughout the wallet, and had been updated before Zcash launched to be aware of spent shielded notes. The change to getbalance exposed a bug: CWalletTx::IsFromMe had not been similarly updated, which caused getbalance to ignore wallet-internal (sent between two addresses in the node’s wallet) unshielding transactions with zero confirmations. This release fixes the bug.

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As always, it is possible that further backwards-incompatible changes might be made to the NU5 consensus rules in this testing phase, prior to setting the mainnet activation height, as we continue to conduct additional internal review. In the event that this happens, testnet will be rolled back in (or prior to) v5.0.0, and a new testnet activation will occur.