Sapling deployment

The primary sources of information about Sapling consensus protocol changes are:

• The Zcash Protocol Specification 2.
• Transaction Signature Validation for Sapling 9.
• Network Upgrade Mechanism 7.

The network handshake and peer management mechanisms defined in 8 also apply to this upgrade.

The following network upgrade constants 7 are defined for the Sapling upgrade:

CONSENSUS_BRANCH_ID

0x76b809bb

ACTIVATION_HEIGHT (Sapling)

Testnet: 280000

Mainnet: 419200

On Testnet, Sapling had activated prior to this height, but that consensus branch was rolled back. A subsequent hard fork occurred on Testnet, changing the difficulty algorithm to accept "minimum-difficulty" blocks under certain conditions starting at block height 299188.

On both Mainnet and Testnet, Sapling-compatible nodes MUST advertise protocol version 170007 or later. The minimum peer protocol version that Sapling-compatible nodes will connect to, remains 170002.

Pre-Sapling nodes are defined as nodes advertising a protocol version less than 170007.

Approximately three days (defined in terms of block height) before the Sapling activation height, Sapling-compatible nodes will change the behaviour of their peer connection logic in order to prefer pre-Sapling peers for eviction from the set of peer connections.

/** The period before a network upgrade activates, where connections to upgrading peers are preferred (in blocks). */
static const int NETWORK_UPGRADE_PEER_PREFERENCE_BLOCK_PERIOD = 24 * 24 * 3;

The implementation is similar to that for Overwinter which was described in 8.

Once Sapling activates on Testnet or Mainnet, Sapling nodes SHOULD take steps to:

• reject new connections from pre-Sapling nodes;
• disconnect any existing connections to pre-Sapling nodes.

Change to difficulty adjustment on Testnet

Section 7.6.3 of the Zcash Protocol Specification 5 describes the algorithm used to adjust the difficulty of a block (defined in terms of a "target threshold") based on the nTime and nBits fields of preceding blocks.

This algorithm changed on Testnet, starting from block 299188, to allow "minimum-difficulty" blocks. If the block time of a block from this height onward is greater than 15 minutes after that of the preceding block, then the block is a minimum-difficulty block. In that case its nBits field MUST be set to ToCompact(PoWLimit), where PoWLimit is the value defined for Testnet in section 5.3 of the Zcash Protocol Specification 4, and ToCompact is as defined in section 7.7.4 of that specification 6.

Note: a previous revision of this ZIP incorrectly said that only the target threshold of minimum-difficulty blocks is affected. In fact the nBits field is modified as well, and this affects difficulty adjustment for subsequent blocks.

This change does not affect Mainnet.