155 lines
5.8 KiB
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155 lines
5.8 KiB
ReStructuredText
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ZIP: 205
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Title: Deployment of the Sapling Network Upgrade
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Owners: Daira Hopwood <daira@electriccoin.co>
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Credits: Simon Liu
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Status: Final
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Category: Consensus / Network
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Created: 2018-10-08
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License: MIT
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Terminology
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===========
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The key words "MUST" and "SHOULD" in this document are to be interpreted as
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described in RFC 2119. [#RFC2119]_
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The terms "consensus branch" and "network upgrade" in this document are to be
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interpreted as described in ZIP 200. [#zip-0200]_
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The terms "Testnet" and "Mainnet" are to be interpreted as described in
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section 3.12 of the Zcash Protocol Specification [#protocol-networks]_.
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The terms below are to be interpreted as follows:
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Sapling
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Code-name for the second Zcash network upgrade, also known as Network Upgrade 1.
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Abstract
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========
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This proposal defines the deployment of the Sapling network upgrade. In addition,
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it describes a hard fork that occurred on Testnet to allow "minimum-difficulty"
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blocks.
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Specification
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=============
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Sapling deployment
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------------------
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The primary sources of information about Sapling consensus protocol changes are:
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- The Zcash Protocol Specification [#protocol]_.
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- Transaction Signature Validation for Sapling [#zip-0243]_.
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- Network Upgrade Mechanism [#zip-0200]_.
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The network handshake and peer management mechanisms defined in [#zip-0201]_ also
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apply to this upgrade.
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The following network upgrade constants [#zip-0200]_ are defined for the Sapling
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upgrade:
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CONSENSUS_BRANCH_ID
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``0x76b809bb``
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ACTIVATION_HEIGHT (Sapling)
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Testnet: 280000
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Mainnet: 419200
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On Testnet, Sapling had activated prior to this height, but that consensus branch
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was rolled back. A subsequent hard fork occurred on Testnet, changing the
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difficulty algorithm to accept "minimum-difficulty" blocks under certain
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conditions starting at block height 299188.
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On both Mainnet and Testnet, Sapling-compatible nodes MUST advertise protocol
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version 170007 or later. The minimum peer protocol version that Sapling-compatible
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nodes will connect to, remains 170002.
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Pre-Sapling nodes are defined as nodes advertising a protocol version less than
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170007.
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Approximately three days (defined in terms of block height) before the Sapling
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activation height, Sapling-compatible nodes will change the behaviour of their peer
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connection logic in order to prefer pre-Sapling peers for eviction from the set of
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peer connections.
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::
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/** The period before a network upgrade activates, where connections to upgrading peers are preferred (in blocks). */
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static const int NETWORK_UPGRADE_PEER_PREFERENCE_BLOCK_PERIOD = 24 * 24 * 3;
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The implementation is similar to that for Overwinter which was described in
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[#zip-0201]_.
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Once Sapling activates on Testnet or Mainnet, Sapling nodes SHOULD take steps to:
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- reject new connections from pre-Sapling nodes;
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- disconnect any existing connections to pre-Sapling nodes.
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Change to difficulty adjustment on Testnet
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------------------------------------------
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Section 7.6.3 of the Zcash Protocol Specification [#protocol-diffadjustment]_
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describes the algorithm used to adjust the difficulty of a block (defined in terms
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of a "target threshold") based on the ``nTime`` and ``nBits`` fields of preceding
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blocks.
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This algorithm changed on Testnet, starting from block 299188, to allow
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"minimum-difficulty" blocks. If the block time of a block from this height onward
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is greater than 15 minutes after that of the preceding block, then the block is a
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minimum-difficulty block. In that case its ``nBits`` field MUST be set to
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ToCompact(PoWLimit), where PoWLimit is the value defined for Testnet in section 5.3
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of the Zcash Protocol Specification [#protocol-constants]_, and ToCompact is as
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defined in section 7.7.4 of that specification [#protocol-nbits]_.
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Note: a previous revision of this ZIP incorrectly said that only the target
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threshold of minimum-difficulty blocks is affected. In fact the ``nBits`` field
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is modified as well, and this affects difficulty adjustment for subsequent blocks.
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This change does not affect Mainnet.
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Backward compatibility
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======================
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Prior to the network upgrade activating, Sapling and pre-Sapling nodes are
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compatible and can connect to each other. However, Sapling nodes will have a
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preference for connecting to other Sapling nodes, so pre-Sapling nodes will
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gradually be disconnected in the run up to activation.
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Once the network upgrades, even though pre-Sapling nodes can still accept the
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numerically larger protocol version used by Sapling as being valid, Sapling nodes
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will always disconnect peers using lower protocol versions.
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Support in zcashd
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=================
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Support for Sapling consensus rules was implemented in zcashd version 2.0.0.
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The majority of support for RPC calls and persistence of Sapling z-addresses
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was implemented in version 2.0.1. Both of these versions advertise protocol
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version 170007.
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References
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==========
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.. [#RFC2119] `RFC 2119: Key words for use in RFCs to Indicate Requirement Levels <https://www.rfc-editor.org/rfc/rfc2119.html>`_
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.. [#protocol] `Zcash Protocol Specification, Version 2021.2.16 or later <protocol/protocol.pdf>`_
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.. [#protocol-networks] `Zcash Protocol Specification, Version 2021.2.16. Section 3.12: Mainnet and Testnet <protocol/protocol.pdf#networks>`_
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.. [#protocol-constants] `Zcash Protocol Specification, Version 2021.2.16. Section 5.3: Constants <protocol/protocol.pdf#constants>`_
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.. [#protocol-diffadjustment] `Zcash Protocol Specification, Version 2021.2.16. Section 7.7.3: Difficulty adjustment <protocol/protocol.pdf#diffadjustment>`_
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.. [#protocol-nbits] `Zcash Protocol Specification, Version 2021.2.16. Section 7.7.4: nBits conversion <protocol/protocol.pdf#nbits>`_
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.. [#zip-0200] `ZIP 200: Network Upgrade Mechanism <zip-0200.rst>`_
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.. [#zip-0201] `ZIP 201: Network Peer Management for Overwinter <zip-0201.rst>`_
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.. [#zip-0243] `ZIP 243: Transaction Signature Validation for Sapling <zip-0243.rst>`_
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