2020-09-14 07:22:13 -07:00
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::
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ZIP: 244
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2021-01-13 15:27:19 -08:00
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Title: Transaction Non-Malleability
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2020-09-14 07:22:13 -07:00
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Owners: Kris Nuttycombe <kris@electriccoin.co>
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2021-01-13 15:27:19 -08:00
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Daira Hopwood <daira@electriccoin.co>
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Status: Draft
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2020-09-14 07:22:13 -07:00
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Category: Consensus
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2021-01-13 15:27:19 -08:00
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Created: 2021-01-06
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License: MIT
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Discussions-To: <https://github.com/zcash/zips/issues/411>
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===========
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Terminology
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===========
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The key words "MUST" and "MUST NOT" in this document are to be interpreted as described in RFC 2119. [#RFC2119]_
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The terms "consensus branch", "epoch", and "network upgrade" in this document are to be interpreted as
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described in ZIP 200. [#zip-0200]_
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========
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Abstract
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========
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This proposal defines a new transaction digest algorithm for the <TBD> network upgrade
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onward, in order to introduce non-malleable transaction identifiers that commit to
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all transaction data except for attestations to transaction validity.
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This proposal also defines a new transaction digest algorithm for signature validation,
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which shares all available structure produced during the construction of transaction
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identifiers, in order to minimize redundant data hashing in validation.
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2021-01-21 16:23:09 -08:00
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This proposal also defines a new name and semantics for the ``hashLightClientRoot`` field of the
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block header, to enable additional commitments to be represented in this hash and to
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provide a mechanism for future extensibility of the set of commitments represented.
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==========
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Motivation
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==========
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In all cases, but particularly in order to support the use of transactions in
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higher-level protocols, any modification of the transaction that has not been
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explicitly permitted (such as via anyone-can-spend inputs) should invalidate
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attestations to spend authority or to the included outputs. Following the activation
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of this proposed change, transaction identifiers will be stable irrespective of
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2021-01-13 15:54:37 -08:00
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any possible malleation of "witness data" such as proofs and transaction
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signatures.
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============
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Requirements
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============
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- Continue to support existing functionality of the protocol (multisig,
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signing modes for transparent inputs).
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- Allow the use of transaction ids, and pairs of the form (transaction id,
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output index) as stable identifiers.
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- A sender must be able to recognize their own transaction, even given allowed
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forms of malleability such as recomputation of transaction signatures.
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- In the case of transparent inputs, it should be possible to create a
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transaction (B) that spends the outputs from a previous transaction (A) even
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before (A) has been mined. This should also be possible in the case that the
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creator of (B) does not wait for confirmations of (A). That is, (B) should remain
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valid so long as any variant of (A) is eventually mined.
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- It should not be possible for an attacker to malleate a transaction in a
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fashion that would result in the transaction being interpreted as a
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double-spend.
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- It should be possible in the future to upgrade the protocol in such a fashion
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that only non-malleable transactions are accepted.
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- It should be possible to use the transaction id unmodified as the value that
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is used to produce a signature hash in the case that the transaction contains
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no transparent inputs, or in the case that only the ``SIGHASH_ALL`` flag is
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used.
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================
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Non-requirements
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================
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In order to support backwards-compatibility with parts of the ecosystem that
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have not yet upgraded to the non-malleable transaction format, it is not an
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initial requirement that all transactions be non-malleable.
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=============
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Specification
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=============
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-------
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Digests
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-------
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All digests are personalized BLAKE2b-256 hashes. In cases where no elements are
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available for hashing (for example, if there are no transparent inputs) the resulting hash
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will be over just the personalization string, providing domain separation even for
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empty data fields.
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TxId Digest
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===========
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A new transaction digest algorithm is defined that constructs the identifier for
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a transaction from a tree of hashes. Each branch of the tree of hashes will
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correspond to a specific subset of transaction data. The overall structure of
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the hash is as follows; each name referenced here will be described in detail
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below:
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txid_digest
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├── header_digest
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├── transparent_digest
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│ ├── prevouts_digest
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│ ├── sequence_digest
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│ └── outputs_digest
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├── sprout_digest
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└── sapling_digest
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├── sapling_spends_digest
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│ ├── sapling_spends_compact_digest
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│ └── sapling_spends_noncompact_digest
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├── sapling_outputs_digest
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│ ├── sapling_outputs_compact_digest
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│ ├── sapling_outputs_memos_digest
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│ └── sapling_outputs_noncompact_digest
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└── valueBalance
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Each node written as ``snake_case`` in this tree is a BLAKE2b-256 hash of its
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children, initialized with a personalization string specific to that branch
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of the tree. Nodes that are not themselves digests are written in ``camelCase``.
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In the specification below, nodes of the tree are presented in depth-first order.
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``txid_digest``
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--------------
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A BLAKE2b-256 hash of the following values ::
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2021-01-20 16:28:39 -08:00
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* T.1: ``header_digest`` (32-byte hash output)
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* T.2: ``transparent_digest`` (32-byte hash output)
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* T.3: ``sprout_digest (32-byte hash output)
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* T.4: ``sapling_digest (32-byte hash output)
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The personalization field of this hash is set to::
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"ZcashTxHash_" || CONSENSUS_BRANCH_ID
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As in ZIP 143 [#zip-0143]_, CONSENSUS_BRANCH_ID is the 4-byte little-endian encoding of
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the consensus branch ID for the epoch of the block containing the transaction. Domain
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separation of the transaction id hash across parallel consensus branches provides replay
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protection: transactions targeted for one consensus branch will not have the same
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transaction identifier on other consensus branches.
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T.1: ``header_digest``
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`````````````````````````
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A BLAKE2b-256 hash of the following values ::
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* T.1a. ``version`` (4-byte little-endian version identifier including overwinter flag)
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* T.1b. ``version_group_id`` (4-byte little-endian version group identifier)
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* T.1c. ``consensus_branch_id`` (4-byte little-endian consensus branch id)
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* T.1d. ``lock_time`` (4-byte little-endian nLockTime value)
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* T.1e. ``expiry_height`` (4-byte little-endian block height)
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The personalization field of this hash is set to::
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"ZTxIdHeadersHash"
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2021-01-20 16:28:39 -08:00
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T.2: ``transparent_digest``
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`````````````````````````
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A BLAKE2b-256 hash of the following values ::
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2021-01-20 16:28:39 -08:00
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* T.2a. ``prevouts_digest`` (32-byte hash)
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* T.2b. ``sequence_digest`` (32-byte hash)
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* T.2c. ``outputs_digest`` (32-byte hash)
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The personalization field of this hash is set to::
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"ZTxIdTranspaHash"
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T.2a: ``prevouts_digest``
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'''''''''''''''''''''''
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A BLAKE2b-256 hash of the field encoding of all ``outpoint``
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field values of transparent inputs to the transaction.
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The personalization field of this hash is set to::
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"ZTxIdPrevoutHash"
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2021-01-20 16:28:39 -08:00
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T.2b: ``sequence_digest``
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'''''''''''''''''''''''
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A BLAKE2b-256 hash of the 32-bit little-endian representation of all ``nSequence``
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field values of transparent inputs to the transaction.
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The personalization field of this hash is set to::
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"ZTxIdSequencHash"
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2021-01-20 16:28:39 -08:00
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T.2c: ``outputs_digest``
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''''''''''''''''''''''
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A BLAKE2b-256 hash of the field encodings of all ``prevout`` field values of
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transparent inputs belonging to the transaction.
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The personalization field of this hash is set to::
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"ZTxIdOutputsHash"
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2021-01-20 16:28:39 -08:00
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T.3: ``sprout_digest``
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`````````````````````````
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A BLAKE2b-256 hash of the non-authorizing components of Sprout ``JSDescription`` values
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belonging to the transaction. For each ``JSDescription``, the following elements are
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appended to the hash ::
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* T.3a. ``vpub_old`` (8-byte signed little-endian)
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* T.3b. ``vpub_new`` (8-byte signed little-endian)
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* T.3c. ``anchor`` (32 bytes)
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* T.3d. ``nullifiers`` (2 x 32 bytes)
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* T.3e. ``commitments`` (2 x 32 bytes)
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* T.3f. ``ephemeral_key`` (32 bytes)
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* T.3g. ``random_seed`` (32 bytes)
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* T.3h. ``macs`` (2 x 32 bytes)
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* T.3i. ``ciphertexts`` (2 x 601 bytes)
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The personalization field of this hash is set to::
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"ZTxIdJSplitsHash"
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2021-01-20 16:28:39 -08:00
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T.4: ``sapling_digest``
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`````````````````````
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The digest of Sapling components is composed of two subtrees which are organized to
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permit easy interoperability with the ``CompactBlock`` representation of Sapling data
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specified by the ZIP 307 Light Client Protocol [#zip-0307]_.
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This digest is a BLAKE2b-256 hash of the following values ::
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2021-01-20 16:28:39 -08:00
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* T.4a. ``sapling_spends_digest`` (32-byte hash)
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* T.4b. ``sapling_outputs_digest`` (32-byte hash)
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* T.4c. ``valueBalance`` (64-bit signed little-endian)
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The personalization field of this hash is set to::
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"ZTxIdSaplingHash"
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2021-01-20 16:28:39 -08:00
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T.4a: ``sapling_spends_digest``
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''''''''''''''''''''''''''''''
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This digest is a BLAKE2b-256 hash of the following values ::
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2021-01-20 16:28:39 -08:00
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* T.4a.i. ``sapling_spends_compact_digest`` (32-byte hash)
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* T.4a.ii. ``sapling_spends_noncompact_digest`` (32-byte hash)
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The personalization field of this hash is set to::
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"ZTxIdSSpendsHash"
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2021-01-20 16:28:39 -08:00
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T.4a.i: ``sapling_spends_compact_digest``
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.......................................
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A BLAKE2b-256 hash of the field encoding of all ``nullifier`` field
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values of Sapling shielded spends belonging to the transaction.
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The personalization field of this hash is set to::
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"ZTxIdSSpendCHash"
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T.4a.ii: ``sapling_spends_noncompact_digest``
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...........................................
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A BLAKE2b-256 hash of the non-nullifier information for all Sapling shielded spends
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belonging to the transaction, excluding zkproof data. For each spend, the following
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elements are included in the hash::
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2021-01-20 16:28:39 -08:00
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* T.4a.ii.1 ``cv`` (field encoding bytes)
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* T.4a.ii.2 ``anchor`` (field encoding bytes)
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* T.4a.ii.3 ``rk`` (field encoding bytes)
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The personalization field of this hash is set to::
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"ZTxIdSSpendNHash"
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2021-01-20 16:28:39 -08:00
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T.4b: ``sapling_outputs_digest``
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'''''''''''''''''''''''''''''''
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This digest is a BLAKE2b-256 hash of the following values ::
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2021-01-20 16:28:39 -08:00
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* T.4a.i. ``sapling_outputs_compact_digest`` (32-byte hash)
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* T.4b.ii. ``sapling_outputs_memos_digest`` (32-byte hash)
|
|
|
|
|
* T.4b.iii. ``sapling_outputs_noncompact_digest`` (32-byte hash)
|
2021-01-13 15:27:19 -08:00
|
|
|
|
|
|
|
|
|
The personalization field of this hash is set to::
|
|
|
|
|
|
|
|
|
|
"ZTxIdSOutputHash"
|
|
|
|
|
|
2021-01-20 16:28:39 -08:00
|
|
|
|
T.4b.i: ``sapling_outputs_compact_digest``
|
2021-01-13 15:27:19 -08:00
|
|
|
|
.........................................
|
|
|
|
|
A BLAKE2b-256 hash of the subset of Sapling output information included in the
|
2021-01-13 15:54:37 -08:00
|
|
|
|
ZIP-307 [#zip-0307]_ ``CompactBlock`` format for all Sapling shielded outputs
|
2021-01-13 15:27:19 -08:00
|
|
|
|
belonging to the transaction. For each output, the following elements are included
|
|
|
|
|
in the hash::
|
|
|
|
|
|
2021-01-20 16:28:39 -08:00
|
|
|
|
* T.4b.i.1 ``cmu`` (field encoding bytes)
|
|
|
|
|
* T.4b.i.2 ``ephemeral_key`` (field encoding bytes)
|
|
|
|
|
* T.4b.i.3 ``enc_ciphertext[..52]`` (First 52 bytes of field encoding)
|
2021-01-13 15:27:19 -08:00
|
|
|
|
|
|
|
|
|
The personalization field of this hash is set to::
|
|
|
|
|
|
|
|
|
|
"ZTxIdSOutC__Hash"
|
|
|
|
|
|
2021-01-20 16:28:39 -08:00
|
|
|
|
T.4a.ii: ``sapling_outputs_memos_digest``
|
2021-01-13 15:27:19 -08:00
|
|
|
|
........................................
|
|
|
|
|
A BLAKE2b-256 hash of the subset of Sapling shielded memo field data for all Sapling
|
|
|
|
|
shielded outputs belonging to the transaction. For each output, the following elements
|
|
|
|
|
are included in the hash::
|
|
|
|
|
|
2021-01-20 16:28:39 -08:00
|
|
|
|
* T.4b.ii.1 ``enc_ciphertext[52..564] (contents of the encrypted memo field)
|
2021-01-13 15:27:19 -08:00
|
|
|
|
|
|
|
|
|
The personalization field of this hash is set to::
|
|
|
|
|
|
|
|
|
|
"ZTxIdSOutM__Hash"
|
|
|
|
|
|
2021-01-20 16:28:39 -08:00
|
|
|
|
T.4a.iii: ``sapling_outputs_noncompact_digest``
|
2021-01-13 15:27:19 -08:00
|
|
|
|
..............................................
|
|
|
|
|
A BLAKE2b-256 hash of the remaining subset of Sapling output information **not** included
|
2021-01-20 16:28:39 -08:00
|
|
|
|
in the ZIP 307 [#zip-0307]_ ``CompactBlock`` format, excluding zkproof data, for all
|
|
|
|
|
Sapling shielded outputs belonging to the transaction. For each output, the following
|
|
|
|
|
elements are included in the hash::
|
2021-01-13 15:27:19 -08:00
|
|
|
|
|
2021-01-20 16:28:39 -08:00
|
|
|
|
* T.4b.iii.1 ``cv`` (field encoding bytes)
|
|
|
|
|
* T.4b.iii.2 ``enc_ciphertext[564..]`` (post-memo suffix of field encoding)
|
|
|
|
|
* T.4b.iii.3 ``out_ciphertext`` (field encoding bytes)
|
2021-01-13 15:27:19 -08:00
|
|
|
|
|
|
|
|
|
The personalization field of this hash is set to::
|
|
|
|
|
|
2021-01-13 15:57:38 -08:00
|
|
|
|
"ZTxIdSOutN__Hash" (2 underscore characters)
|
2021-01-13 15:27:19 -08:00
|
|
|
|
|
2021-01-20 16:28:39 -08:00
|
|
|
|
Signature Digest
|
|
|
|
|
================
|
|
|
|
|
|
2021-01-26 13:31:47 -08:00
|
|
|
|
A new per-input transaction digest algorithm is defined that constructs a hash that may be
|
|
|
|
|
signed by a transaction creator to commit to the effects of the transaction. In the case
|
|
|
|
|
that the transaction consumes no transparent inputs, it should be possible to just sign
|
|
|
|
|
the transaction identifier produced by the ``TxId Digest`` algorithm. In the case that
|
|
|
|
|
transparent inputs are present, this algorithm follows closely the ZIP 143 [#zip-0143]_
|
|
|
|
|
algorithm.
|
2021-01-20 16:28:39 -08:00
|
|
|
|
|
|
|
|
|
The overall structure of the hash is as follows; each name referenced here will be
|
|
|
|
|
described in detail below:
|
|
|
|
|
|
|
|
|
|
signature_digest
|
|
|
|
|
├── header_digest
|
|
|
|
|
├── transparent_digest
|
|
|
|
|
├── sprout_digest
|
|
|
|
|
└── sapling_digest
|
|
|
|
|
|
|
|
|
|
``signature_digest``
|
|
|
|
|
--------------------
|
|
|
|
|
A BLAKE2b-256 hash of the following values ::
|
|
|
|
|
|
|
|
|
|
* S.1: ``header_digest`` (32-byte hash output)
|
|
|
|
|
* S.2: ``transparent_digest`` (32-byte hash output)
|
|
|
|
|
* S.3: ``sprout_digest (32-byte hash output)
|
|
|
|
|
* S.4: ``sapling_digest (32-byte hash output)
|
|
|
|
|
|
|
|
|
|
The personalization field of this hash is set to::
|
|
|
|
|
|
|
|
|
|
"ZcashTxHash_" || CONSENSUS_BRANCH_ID
|
|
|
|
|
|
|
|
|
|
This value must have the same personalization as the top hash of the transaction
|
|
|
|
|
identifier digest tree, in order to make it possible to sign the transaction id
|
|
|
|
|
in the case that there are no transparent inputs.
|
|
|
|
|
|
|
|
|
|
S.1: ``header_digest``
|
|
|
|
|
`````````````````````````
|
|
|
|
|
Identical to that specified for the transaction identifier.
|
|
|
|
|
|
|
|
|
|
S.2: ``transparent_digest``
|
|
|
|
|
`````````````````````````
|
|
|
|
|
If we are producing a hash for the signature over a transparent input,
|
|
|
|
|
the value of the digest produced here depends upon the value of a ``hash_type``
|
2021-01-21 16:23:09 -08:00
|
|
|
|
flag as in ZIP 143 [#zip-0143]_.
|
2021-01-20 16:28:39 -08:00
|
|
|
|
|
|
|
|
|
The construction of each component below depends upon the values of the
|
2021-01-21 16:23:09 -08:00
|
|
|
|
``hash_type`` flag bits. Each component will be described separately
|
2021-01-20 16:28:39 -08:00
|
|
|
|
|
|
|
|
|
This digest is a BLAKE2b-256 hash of the following values ::
|
|
|
|
|
|
|
|
|
|
* S.2a. ``prevouts_digest`` (32-byte hash)
|
|
|
|
|
* S.2b. ``sequence_digest`` (32-byte hash)
|
|
|
|
|
* S.2c. ``outputs_digest`` (32-byte hash)
|
|
|
|
|
* S.2d. ``txin_sig_digest`` (32-byte hash)
|
|
|
|
|
|
|
|
|
|
The personalization field of this hash is set to::
|
|
|
|
|
|
|
|
|
|
"ZTxIdTranspaHash"
|
|
|
|
|
|
|
|
|
|
S.2a: ``prevouts_digest``
|
|
|
|
|
'''''''''''''''''''''''
|
|
|
|
|
This is a BLAKE2b-256 hash initialized with the personalization field value
|
|
|
|
|
"ZTxIdPrevoutHash".
|
|
|
|
|
|
2021-01-21 16:23:09 -08:00
|
|
|
|
If the ``SIGHASH_ANYONECANPAY`` flag is not set::
|
2021-01-20 16:28:39 -08:00
|
|
|
|
|
2021-01-21 16:23:09 -08:00
|
|
|
|
* identical to the value of ``prevouts_digest`` as specified for the
|
|
|
|
|
transaction identifier in section T.2a.
|
2021-01-20 16:28:39 -08:00
|
|
|
|
|
|
|
|
|
otherwise::
|
|
|
|
|
|
2021-01-21 16:23:09 -08:00
|
|
|
|
* the hash is immediately finalized, without being updated with any
|
|
|
|
|
additional data
|
2021-01-20 16:28:39 -08:00
|
|
|
|
|
|
|
|
|
S.2b: ``sequence_digest``
|
|
|
|
|
'''''''''''''''''''''''
|
|
|
|
|
This is a BLAKE2b-256 hash initialized with the personalization field value
|
|
|
|
|
"ZTxIdSequencHash".
|
|
|
|
|
|
2021-01-21 16:23:09 -08:00
|
|
|
|
If none of the ``SIGHASH_ANYONECANPAY``, ``SIGHASH_SINGLE``, or ``SIGHASH_NONE`` flags are
|
2021-01-20 16:28:39 -08:00
|
|
|
|
set::
|
|
|
|
|
|
2021-01-21 16:23:09 -08:00
|
|
|
|
* identical to the value of ``sequence_digest`` as specified for the
|
|
|
|
|
transaction identifier in section T.2b.
|
2021-01-20 16:28:39 -08:00
|
|
|
|
|
|
|
|
|
otherwise::
|
|
|
|
|
|
2021-01-21 16:23:09 -08:00
|
|
|
|
* the hash is immediately finalized, without being updated with any
|
|
|
|
|
additional data
|
2021-01-20 16:28:39 -08:00
|
|
|
|
|
|
|
|
|
S.2c: ``outputs_digest``
|
|
|
|
|
'''''''''''''''''''''''
|
|
|
|
|
This is a BLAKE2b-256 hash initialized with the personalization field value
|
|
|
|
|
"ZTxIdOutputsHash".
|
|
|
|
|
|
2021-01-21 16:23:09 -08:00
|
|
|
|
If none of the ``SIGHASH_SINGLE`` or ``SIGHASH_NONE`` flags are set::
|
2021-01-20 16:28:39 -08:00
|
|
|
|
|
2021-01-21 16:23:09 -08:00
|
|
|
|
* identical to the value of ``outputs_digest`` as specified for the
|
|
|
|
|
transaction identifier in section T.2c.
|
|
|
|
|
|
|
|
|
|
If the ``SIGHASH_SINGLE`` flag is set and the signature hash is being computed for
|
|
|
|
|
the transparent input at a particular index, and a transparent output appears in
|
|
|
|
|
the transaction at that index::
|
|
|
|
|
|
|
|
|
|
* the hash is updated with the transaction serialized form of the
|
|
|
|
|
transparent output at that index, and finalized.
|
2021-01-20 16:28:39 -08:00
|
|
|
|
|
|
|
|
|
If the ``SIGHASH_SINGLE`` flag is set and the signature is being computed for
|
|
|
|
|
a shielded input, or if the ``SIGHASH_NONE`` flag is set::
|
|
|
|
|
|
|
|
|
|
* the hash is immediately finalized, without being updated with any
|
|
|
|
|
additional data
|
|
|
|
|
|
|
|
|
|
S.2d: ``txin_sig_digest``
|
|
|
|
|
'''''''''''''''''''''''''
|
|
|
|
|
This is a BLAKE2b-256 hash initialized with the personalization field value
|
|
|
|
|
"Zcash___TxInHash" (3 underscores).
|
|
|
|
|
|
|
|
|
|
If the signature hash is being computed for a transparent input, the hash
|
|
|
|
|
is updated with the following properties of that input::
|
|
|
|
|
|
|
|
|
|
* S.2d.i. ``prevout`` (field encoding)
|
|
|
|
|
* S.2d.ii. ``script_code`` (field encoding)
|
|
|
|
|
* S.2d.iii. ``value`` (8-byte signed little-endian)
|
|
|
|
|
* S.2d.iv. ``nSequence`` (4-byte unsigned little-endian)
|
|
|
|
|
|
|
|
|
|
otherwise::
|
|
|
|
|
|
|
|
|
|
* the hash is immediately finalized, without being updated with any
|
|
|
|
|
additional data
|
|
|
|
|
|
|
|
|
|
S.3: ``sprout_digest``
|
|
|
|
|
`````````````````````````
|
|
|
|
|
Identical to that specified for the transaction identifier.
|
|
|
|
|
|
|
|
|
|
S.4: ``sapling_digest``
|
|
|
|
|
`````````````````````````
|
|
|
|
|
Identical to that specified for the transaction identifier.
|
|
|
|
|
|
2021-01-21 11:52:53 -08:00
|
|
|
|
Authorizing Data Commitment
|
|
|
|
|
===========================
|
2021-01-13 15:27:19 -08:00
|
|
|
|
|
|
|
|
|
A new transaction digest algorithm is defined that constructs a digest which commits
|
|
|
|
|
to the authorizing data of a transaction from a tree of BLAKE2b-256 hashes.
|
|
|
|
|
The overall structure of the hash is as follows:
|
|
|
|
|
|
2021-01-13 15:57:38 -08:00
|
|
|
|
auth_digest
|
|
|
|
|
├── transparent_scripts_digest
|
|
|
|
|
├── sprout_sigs_digest
|
|
|
|
|
└── sapling_sigs_digest
|
2021-01-13 15:27:19 -08:00
|
|
|
|
|
|
|
|
|
Each node written as ``snake_case`` in this tree is a BLAKE2b-256 hash of authorizing
|
|
|
|
|
data of the transaction.
|
|
|
|
|
|
2021-01-20 16:28:39 -08:00
|
|
|
|
The pair (Transaction Identifier, Auth Commitment) constitutes a commitment to all the
|
|
|
|
|
data of a serialized transaction that may be included in a block.
|
|
|
|
|
|
2021-01-13 15:27:19 -08:00
|
|
|
|
``auth_digest``
|
|
|
|
|
--------------
|
|
|
|
|
A BLAKE2b-256 hash of the following values ::
|
|
|
|
|
|
|
|
|
|
* ``transparent_scripts_digest`` (32-byte hash output)
|
2021-01-20 16:28:39 -08:00
|
|
|
|
* ``sprout_auth_digest (32-byte hash output)
|
|
|
|
|
* ``sapling_auth_digest (32-byte hash output)
|
2021-01-13 15:27:19 -08:00
|
|
|
|
|
|
|
|
|
The personalization field of this hash is set to::
|
|
|
|
|
|
2021-01-26 13:31:47 -08:00
|
|
|
|
"ZTxAuthHash_" || CONSENSUS_BRANCH_ID
|
2021-01-13 15:27:19 -08:00
|
|
|
|
|
|
|
|
|
1: ``transparent_scripts_digest``
|
|
|
|
|
`````````````````````````````````
|
|
|
|
|
A BLAKE2b-256 hash of the field encoding of the Bitcoin script associated
|
|
|
|
|
with each transparent input belonging to the transaction.
|
|
|
|
|
|
|
|
|
|
The personalization field of this hash is set to::
|
|
|
|
|
|
|
|
|
|
"ZTxAuthTransHash"
|
|
|
|
|
|
2021-01-20 16:28:39 -08:00
|
|
|
|
2: ``sprout_auth_digest``
|
2021-01-13 15:27:19 -08:00
|
|
|
|
```````````````````````````
|
2021-01-26 13:31:47 -08:00
|
|
|
|
A BLAKE2b-256 hash of the field encoding of the ``zkproof`` values of each
|
|
|
|
|
``JSDescription`` belonging to the transaction, followed by the
|
|
|
|
|
``joinsplit_pubkey`` and ``joinsplit_sig``.
|
2021-01-20 16:28:39 -08:00
|
|
|
|
|
|
|
|
|
* 2a. ``zkproofs`` (field encoding bytes)
|
|
|
|
|
* 2b. ``joinsplit_pubkey``
|
|
|
|
|
* 2b. ``joinsplit_sig``
|
2021-01-13 15:27:19 -08:00
|
|
|
|
|
|
|
|
|
The personalization field of this hash is set to::
|
|
|
|
|
|
|
|
|
|
"ZTxAuthSprouHash"
|
|
|
|
|
|
2021-01-20 16:28:39 -08:00
|
|
|
|
3: ``sapling_auth_digest``
|
2021-01-13 15:27:19 -08:00
|
|
|
|
```````````````````````````
|
2021-01-20 16:28:39 -08:00
|
|
|
|
A BLAKE2b-256 hash of the field encoding of the Sapling zkproof values
|
|
|
|
|
of each Sapling spend description and output description belonging to
|
|
|
|
|
the transaction, followed by the field encoding of the binding signature ::
|
|
|
|
|
|
|
|
|
|
* 3a. ``spend_zkproofs`` (field encoding bytes)
|
|
|
|
|
* 3b. ``output_zkproofs`` (field encoding bytes)
|
|
|
|
|
* 3c. ``binding_sig``
|
2021-01-13 15:27:19 -08:00
|
|
|
|
|
|
|
|
|
The personalization field of this hash is set to::
|
|
|
|
|
|
|
|
|
|
"ZTxAuthSapliHash"
|
|
|
|
|
|
|
|
|
|
--------------------
|
|
|
|
|
Block Header Changes
|
|
|
|
|
--------------------
|
|
|
|
|
|
2021-01-21 11:52:53 -08:00
|
|
|
|
The nonmalleable transaction identifier specified by this ZIP will be used
|
|
|
|
|
in the place of the current malleable transaction identifier within the
|
2021-01-26 07:47:57 -08:00
|
|
|
|
Merkle tree committed to by the ``hashMerkleRoot`` value. However, this
|
2021-01-21 11:52:53 -08:00
|
|
|
|
change now means that ``hashMerkleRoot`` is not sufficient to fully commit
|
|
|
|
|
to the transaction data, including witnesses, that appear within the block.
|
|
|
|
|
|
|
|
|
|
As a consequence, we now need to add a new commitment to the block header.
|
|
|
|
|
This commitment will be the root of a Merkle tree that has parallel structure
|
2021-01-26 07:47:57 -08:00
|
|
|
|
to the tree committed to by ``hashMerkleRoot`` (the position of the transaction
|
|
|
|
|
in this Merkle tree identifies the same transaction as the same position in the
|
|
|
|
|
tree rooted at ``hashMerkleRoot``) but where the leaves are hashes produced
|
|
|
|
|
according to the :ref:`Authorizing Data Commitment<Authorizing Data Commitment>`
|
2021-01-21 11:52:53 -08:00
|
|
|
|
specification.
|
|
|
|
|
|
|
|
|
|
This new commitment is named ``hashAuthDataRoot`` and is the root of a left-dense
|
2021-01-26 07:47:57 -08:00
|
|
|
|
binary Merkle tree of transaction-authorizing data commitments. Empty internal nodes
|
|
|
|
|
and leaves in the Merkle tree (nodes without children) have the "null" hash value
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``[0u8; 32]``. Hashes in this tree are BLAKE2b-256 hashes, personalized by the string
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``"ZcashAuthDatHash"``.
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Changing the block header format to allow space for an additional
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commitment is somewhat invasive. Instead, the name and meaning of the
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``hashLightClientRoot`` field is changed.
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2021-01-21 11:52:53 -08:00
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``hashLightClientRoot`` is renamed to ``hashBlockCommitments``. The value
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of this hash is the BLAKE2b-256 hash personalized by the string ``"ZcashBlockCommit"``
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of the following elements:
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2021-01-21 11:52:53 -08:00
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* ``hashLightClientRoot`` as described in ZIP 221 [#zip-0221]_
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* ``hashAuthDataRoot``
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* ``terminator`` [0u8;32]
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This representation treats the ``hashBlockCommitments`` value as a linked
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list of hashes terminated by arbitrary data. In the case of protocol upgrades
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where additional commitments need to be included in the block header, it is
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possible to replace this terminator with the hash of a newly defined structure
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which ends in a similar terminator. Fully validating nodes MUST always use the
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entire structure defined by the latest activated protocol version that they
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support.
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The linked structure of this hash is intended to provide extensibility for
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use by light clients which may be connected to a third-party server that supports
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a later protocol version. Such a third party SHOULD provide a value that can
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be used instead of the all-zeros terminator to permit the light client to
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perform validation of the parts of the structure it needs.
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2021-01-13 15:27:19 -08:00
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========================
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Reference implementation
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========================
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- https://github.com/zcash/librustzcash/pull/319/files
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==========
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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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.. [#zip-0200] `ZIP 200: Network Upgrade Activation Mechanism <zip-0200.rst>`_
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.. [#zip-0221] `ZIP 221: FlyClient - Consensus Layer Changes <zip-0221.rst>`_
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.. [#zip-0076] `ZIP 76: Transaction Signature Validation before Overwinter <zip-0076.rst>`_
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.. [#zip-0143] `ZIP 143: Transaction Signature Validation for Overwinter <zip-0143.rst>`_
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.. [#zip-0307] `ZIP 307: Light Client Protocol for Payment Detection <zip-0307.rst>`_
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