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docs: document consensus rules from 7.3 Spend Description Encoding and Consensus (#3575)

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Conrado Gouvea 2022-02-18 23:27:09 -03:00 committed by GitHub
parent 5b306fd86e
commit ab03a376ef
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2 changed files with 12 additions and 18 deletions
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10
zebra-chain/src/sapling/spend.rs
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@ -193,12 +193,20 @@ impl ZcashDeserialize for Spend<PerSpendAnchor> {
// https://zips.z.cash/protocol/protocol.pdf#spenddesc
//
// See comments below for each specific type.
//
// > LEOS2IP_{256}(anchorSapling), if present, MUST be less than 𝑞_𝕁.
//
// https://zips.z.cash/protocol/protocol.pdf#spendencodingandconsensus
//
// Applies to `per_spend_anchor` below; validated in
// [`crate::sapling::tree::Root::zcash_deserialize`].
Ok(Spend {
// Type is `ValueCommit^{Sapling}.Output`, i.e. J
// https://zips.z.cash/protocol/protocol.pdf#abstractcommit
// See [`commitment::NotSmallOrderValueCommitment::zcash_deserialize`].
cv: commitment::NotSmallOrderValueCommitment::zcash_deserialize(&mut reader)?,
// Type is `B^{[ℓ_{Sapling}_{Merkle}]}`, i.e. 32 bytes
// Type is `B^{[ℓ_{Sapling}_{Merkle}]}`, i.e. 32 bytes.
// But as mentioned above, we validate it further as an integer.
per_spend_anchor: (&mut reader).zcash_deserialize_into()?,
// Type is `B^Y^{[ℓ_{PRFnfSapling}/8]}`, i.e. 32 bytes
nullifier: note::Nullifier::from(reader.read_32_bytes()?),

20
zebra-chain/src/transaction/serialize.rs
View File

@ -207,13 +207,11 @@ impl ZcashDeserialize for Option<sapling::ShieldedData<SharedAnchor>> {
//
// Type is `B^{[ℓ_{Sapling}_{Merkle}]}`, i.e. 32 bytes
//
// # Consensus
// > LEOS2IP_{256}(anchorSapling), if present, MUST be less than 𝑞_𝕁.
//
// > Elements of a Spend description MUST be valid encodings of the types given above.
// https://zips.z.cash/protocol/protocol.pdf#spendencodingandconsensus
//
// https://zips.z.cash/protocol/protocol.pdf#spenddesc
//
// Type is `B^{[ℓ_{Sapling}_{Merkle}]}`, i.e. 32 bytes
// Validated in [`crate::sapling::tree::Root::zcash_deserialize`].
let shared_anchor = if spends_count > 0 {
Some((&mut reader).zcash_deserialize_into()?)
} else {
@ -233,18 +231,6 @@ impl ZcashDeserialize for Option<sapling::ShieldedData<SharedAnchor>> {
// It is not enforced here; this just reads 192 bytes.
// The type is validated when validating the proof, see
// [`groth16::Item::try_from`]. In #3179 we plan to validate here instead.
//
// # Consensus
//
// > Elements of a Spend description MUST be valid encodings of the types given above.
//
// https://zips.z.cash/protocol/protocol.pdf#spenddesc
//
// Type is `ZKSpend.Proof`, described in
// https://zips.z.cash/protocol/protocol.pdf#grothencoding
// It is not enforced here; this just reads 192 bytes.
// The type is validated when validating the proof, see
// [`groth16::Item::try_from`]. In #3179 we plan to validate here instead.
let spend_proofs = zcash_deserialize_external_count(spends_count, &mut reader)?;
// Denoted as `vSpendAuthSigsSapling` in the spec.