zcash_proofs: Implement batch validation for Sapling bundles
We use the `redjubjub` crate for batch validation, because the demo batch validation API in `zcash_primitives::redjubjub` cannot be used outside that crate, and using `redjubjub` enables this to be published as a point release of `zcash_proofs`.
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@ -6,6 +6,8 @@ and this library adheres to Rust's notion of
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[Semantic Versioning](https://semver.org/spec/v2.0.0.html).
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## [Unreleased]
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### Added
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- `zcash_proofs::sapling::BatchValidator`
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## [0.7.0] - 2022-06-24
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### Changed
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@ -27,6 +27,8 @@ jubjub = "0.9"
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lazy_static = "1"
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minreq = { version = "2", features = ["https"], optional = true }
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rand_core = "0.6"
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redjubjub = "0.5"
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tracing = "0.1"
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wagyu-zcash-parameters = { version = "0.2", optional = true }
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zcash_primitives = { version = "0.7", path = "../zcash_primitives" }
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@ -8,7 +8,7 @@ mod prover;
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mod verifier;
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pub use self::prover::SaplingProvingContext;
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pub use self::verifier::SaplingVerificationContext;
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pub use self::verifier::{BatchValidator, SaplingVerificationContext};
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// This function computes `value` in the exponent of the value commitment base
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fn compute_value_balance(value: Amount) -> Option<jubjub::ExtendedPoint> {
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@ -11,6 +11,9 @@ use super::compute_value_balance;
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mod single;
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pub use single::SaplingVerificationContext;
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mod batch;
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pub use batch::BatchValidator;
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/// A context object for verifying the Sapling components of a Zcash transaction.
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struct SaplingVerificationContextInner {
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// (sum of the Spend value commitments) - (sum of the Output value commitments)
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@ -28,7 +31,7 @@ impl SaplingVerificationContextInner {
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/// Perform consensus checks on a Sapling SpendDescription, while
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/// accumulating its value commitment inside the context for later use.
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#[allow(clippy::too_many_arguments)]
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fn check_spend(
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fn check_spend<C>(
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&mut self,
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cv: jubjub::ExtendedPoint,
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anchor: bls12_381::Scalar,
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@ -37,8 +40,9 @@ impl SaplingVerificationContextInner {
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sighash_value: &[u8; 32],
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spend_auth_sig: Signature,
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zkproof: Proof<Bls12>,
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spend_auth_sig_verifier: impl FnOnce(PublicKey, [u8; 64], Signature) -> bool,
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proof_verifier: impl FnOnce(Proof<Bls12>, [bls12_381::Scalar; 7]) -> bool,
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verifier_ctx: &mut C,
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spend_auth_sig_verifier: impl FnOnce(&mut C, PublicKey, [u8; 64], Signature) -> bool,
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proof_verifier: impl FnOnce(&mut C, Proof<Bls12>, [bls12_381::Scalar; 7]) -> bool,
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) -> bool {
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if (cv.is_small_order() | rk.0.is_small_order()).into() {
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return false;
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@ -57,7 +61,7 @@ impl SaplingVerificationContextInner {
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// Verify the spend_auth_sig
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let rk_affine = rk.0.to_affine();
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if !spend_auth_sig_verifier(rk, data_to_be_signed, spend_auth_sig) {
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if !spend_auth_sig_verifier(verifier_ctx, rk, data_to_be_signed, spend_auth_sig) {
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return false;
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}
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@ -89,7 +93,7 @@ impl SaplingVerificationContextInner {
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}
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// Verify the proof
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proof_verifier(zkproof, public_input)
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proof_verifier(verifier_ctx, zkproof, public_input)
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}
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/// Perform consensus checks on a Sapling OutputDescription, while
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@ -0,0 +1,174 @@
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use bellman::groth16;
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use bls12_381::Bls12;
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use group::GroupEncoding;
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use rand_core::{CryptoRng, RngCore};
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use zcash_primitives::transaction::components::sapling::{Authorized, Bundle};
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use super::SaplingVerificationContextInner;
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/// Batch validation context for Sapling.
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///
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/// This batch-validates Spend and Output proofs, and RedJubjub signatures.
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///
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/// Signatures are verified assuming ZIP 216 is active.
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pub struct BatchValidator {
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bundles_added: bool,
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spend_proofs: groth16::batch::Verifier<Bls12>,
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output_proofs: groth16::batch::Verifier<Bls12>,
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signatures: redjubjub::batch::Verifier,
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}
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impl Default for BatchValidator {
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fn default() -> Self {
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Self::new()
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}
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}
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impl BatchValidator {
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/// Constructs a new batch validation context.
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pub fn new() -> Self {
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BatchValidator {
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bundles_added: false,
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spend_proofs: groth16::batch::Verifier::new(),
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output_proofs: groth16::batch::Verifier::new(),
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signatures: redjubjub::batch::Verifier::new(),
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}
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}
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/// Checks the bundle against Sapling-specific consensus rules, and adds its proof and
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/// signatures to the validator.
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///
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/// Returns `false` if the bundle doesn't satisfy all of the consensus rules. This
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/// `BatchValidator` can continue to be used regardless, but some or all of the proofs
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/// and signatures from this bundle may have already been added to the batch even if
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/// it fails other consensus rules.
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pub fn check_bundle(&mut self, bundle: Bundle<Authorized>, sighash: [u8; 32]) -> bool {
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self.bundles_added = true;
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let mut ctx = SaplingVerificationContextInner::new();
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for spend in bundle.shielded_spends {
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// Deserialize the proof
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let zkproof = match groth16::Proof::read(&spend.zkproof[..]) {
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Ok(p) => p,
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Err(_) => return false,
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};
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// Check the Spend consensus rules, and batch its proof and spend
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// authorization signature.
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let consensus_rules_passed = ctx.check_spend(
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spend.cv,
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spend.anchor,
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&spend.nullifier.0,
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spend.rk,
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&sighash,
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spend.spend_auth_sig,
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zkproof,
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self,
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|this, rk, _, spend_auth_sig| {
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let rk = redjubjub::VerificationKeyBytes::<redjubjub::SpendAuth>::from(
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rk.0.to_bytes(),
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);
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let spend_auth_sig = {
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let mut buf = [0; 64];
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spend_auth_sig.write(&mut buf[..]).unwrap();
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redjubjub::Signature::<redjubjub::SpendAuth>::from(buf)
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};
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this.signatures.queue((rk, spend_auth_sig, &sighash));
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true
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},
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|this, proof, public_inputs| {
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this.spend_proofs.queue((proof, public_inputs.to_vec()));
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true
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},
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);
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if !consensus_rules_passed {
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return false;
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}
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}
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for output in bundle.shielded_outputs {
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// Deserialize the ephemeral key
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let epk = match jubjub::ExtendedPoint::from_bytes(&output.ephemeral_key.0).into() {
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Some(p) => p,
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None => return false,
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};
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// Deserialize the proof
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let zkproof = match groth16::Proof::read(&output.zkproof[..]) {
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Ok(p) => p,
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Err(_) => return false,
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};
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// Check the Output consensus rules, and batch its proof.
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let consensus_rules_passed = ctx.check_output(
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output.cv,
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output.cmu,
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epk,
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zkproof,
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|proof, public_inputs| {
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self.output_proofs.queue((proof, public_inputs.to_vec()));
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true
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},
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);
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if !consensus_rules_passed {
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return false;
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}
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}
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// Check the whole-bundle consensus rules, and batch the binding signature.
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ctx.final_check(
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bundle.value_balance,
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&sighash,
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bundle.authorization.binding_sig,
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|bvk, _, binding_sig| {
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let bvk =
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redjubjub::VerificationKeyBytes::<redjubjub::Binding>::from(bvk.0.to_bytes());
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let binding_sig = {
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let mut buf = [0; 64];
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binding_sig.write(&mut buf[..]).unwrap();
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redjubjub::Signature::<redjubjub::Binding>::from(buf)
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};
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self.signatures.queue((bvk, binding_sig, &sighash));
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true
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},
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)
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}
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/// Batch-validates the accumulated bundles.
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///
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/// Returns `true` if every proof and signature in every bundle added to the batch
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/// validator is valid, or `false` if one or more are invalid. No attempt is made to
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/// figure out which of the accumulated bundles might be invalid; if that information
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/// is desired, construct separate [`BatchValidator`]s for sub-batches of the bundles.
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pub fn validate<R: RngCore + CryptoRng>(
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self,
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spend_vk: &groth16::VerifyingKey<Bls12>,
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output_vk: &groth16::VerifyingKey<Bls12>,
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mut rng: R,
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) -> bool {
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if !self.bundles_added {
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// An empty batch is always valid, but is not free to run; skip it.
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return true;
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}
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if let Err(e) = self.signatures.verify(&mut rng) {
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tracing::debug!("Signature batch validation failed: {}", e);
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return false;
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}
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if self.spend_proofs.verify(&mut rng, spend_vk).is_err() {
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tracing::debug!("Spend proof batch validation failed");
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return false;
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}
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if self.output_proofs.verify(&mut rng, output_vk).is_err() {
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tracing::debug!("Output proof batch validation failed");
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return false;
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}
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true
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}
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}
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@ -46,7 +46,8 @@ impl SaplingVerificationContext {
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sighash_value,
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spend_auth_sig,
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zkproof,
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|rk, msg, spend_auth_sig| {
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&mut (),
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|_, rk, msg, spend_auth_sig| {
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rk.verify_with_zip216(
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&msg,
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&spend_auth_sig,
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zip216_enabled,
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)
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},
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|proof, public_inputs| verify_proof(verifying_key, &proof, &public_inputs[..]).is_ok(),
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|_, proof, public_inputs| {
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verify_proof(verifying_key, &proof, &public_inputs[..]).is_ok()
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},
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)
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}
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