ZIP: 245 Title: Transaction Identifier Digests & Signature Validation for Transparent Zcash Extensions Owners: Kris Nuttycombe <[email protected]> Status: Draft Category: Consensus Created: 2021-01-13 License: MIT Discussions-To: <https://github.com/zcash/zips/issues/384>
The key words "MUST" and "MUST NOT" in this document are to be interpreted as described in RFC 2119. [1]
The terms "consensus branch", "epoch", and "network upgrade" in this document are to be interpreted as described in ZIP 200. [2]
This proposal defines changes to ZIP 244 [4] transaction id and signature digest algorithms to accommodate the inclusion of transparent Zcash extensions (TZEs) as defined in ZIP 222 [3].
The tree of hashes defined by ZIP 244 [4] is re-structured to include a new
branch for TZE hashes. The tze_digest
branch is the only new addition to the
tree; header_digest
, transparent_digest
, sprout_digest
, and sapling_digest
are as in ZIP 244:
txid_digest ├── header_digest ├── transparent_digest ├── tze_digest │ ├── tzein_digest │ └── tzeout_digest ├── sprout_digest └── sapling_digest
The top hash of the txid_digest
tree is modified from the ZIP 244 structure
to be a BLAKE2b-256 hash of the following values
T.1: header_digest (32-byte hash output) T.2: transparent_digest (32-byte hash output) T.3: tze_digest (32-byte hash output) T.4: sprout_digest (32-byte hash output) T.5: sapling_digest (32-byte hash output)
The personalization field of this hash is unmodified from ZIP 244.
A BLAKE2b-256 hash of the following values
T.2a: tzein_digest (32-byte hash) T.2b: tzeout_digest (32-byte hash)
The personalization field of this hash is set to:
"ZTxIdTZE____Hash" (4 underscore characters)
A BLAKE2b-256 hash of all TZE inputs to the transaction, excluding witness data. For each TZE input, the following values are appended to this hash:
2a.i: extension_id (CompactSize field encoding) 2a.ii: mode (CompactSize field encoding)
The personalization field of this hash is set to:
"ZTxIdTZEIns_Hash" (1 underscore character)
A BLAKE2b-256 hash of the field encoding of all TZE outputs belonging to the transaction.
The personalization field of this hash is set to:
"ZTxIdTzeOutsHash"
The signature digest creation algorithm defined by ZIP 244 [4] is modified to
include a new branch for TZE hashes. The tze_digest
branch is the only new addition
to the tree; header_digest
, transparent_digest
, sprout_digest
, and
sapling_digest
are as in ZIP 244:
signature_digest ├── header_digest ├── transparent_digest ├── tze_digest │ ├── tzein_digest │ └── tzeout_digest ├── sprout_digest └── sapling_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: tze_digest (32-byte hash output) S.4: sprout_digest (32-byte hash output) S.5: sapling_digest (32-byte hash output)
The personalization field of this hash is set to:
"ZcashTxHash_" || CONSENSUS_BRANCH_ID
ZcashTxHash_
has 1 underscore character.
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.
This digest is a BLAKE2b-256 hash of the following values of the TZE input being signed:
S.3a: prevout_digest (field encoding bytes) S.3b: extension_id (CompactSize field encoding) S.3c: mode (CompactSize field encoding) S.3d: payload (arbitrary bytes) S.3e: value (8-byte little endian value of the output spent by this input)
The personalization field of this hash is set to:
"Zcash__TzeInHash" (2 underscore characters)
The tree of hashes defined by ZIP 244 [4] for authorizing data commitments is
re-structured to include a new branch for TZE hashes. The tze_witnesses_digest
branch
is the only new addition to the tree; transparent_auth_digest
, sprout_auth_digest
,
and sapling_auth_digest
are as in ZIP 244:
auth_digest ├── transparent_scripts_digest ├── tze_witnesses_digest ├── sprout_auth_digest └── sapling_auth_digest
The top hash of the auth_digest
tree is modified from the ZIP 244 structure
to be a BLAKE2b-256 hash of the following values
A.1: transparent_scripts_digest (32-byte hash output) A.2: tze_witnesses_digest (32-byte hash output) A.3: sprout_auth_digest (32-byte hash output) A.4: sapling_auth_digest (32-byte hash output)
The personalization field of this hash is unmodified from ZIP 244.
A BLAKE2b-256 hash of the field encoding of the witness payload
data associated
with each TZE input belonging to the transaction.
The personalization field of this hash is set to:
"ZTxAuthTZE__Hash" (2 underscore characters)
[1] | RFC 2119: Key words for use in RFCs to Indicate Requirement Levels |
[2] | ZIP 200: Network Upgrade Activation Mechanism |
[3] | ZIP 222: Transparent Zcash Extensions |
[4] | (1, 2, 3, 4) ZIP 244: Transaction Identifier Non-Malleability |