422 lines
16 KiB
Rust
422 lines
16 KiB
Rust
//! Async Groth16 batch verifier service
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use std::{
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convert::{TryFrom, TryInto},
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error::Error,
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fmt,
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future::Future,
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mem,
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pin::Pin,
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task::{Context, Poll},
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};
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use bellman::{
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gadgets::multipack,
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groth16::{batch, VerifyingKey},
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VerificationError,
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};
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use bls12_381::Bls12;
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use futures::future::{ready, Ready};
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use once_cell::sync::Lazy;
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use rand::thread_rng;
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use tokio::sync::broadcast::{channel, error::RecvError, Sender};
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use tower::{util::ServiceFn, Service};
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use tower_batch::{Batch, BatchControl};
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use tower_fallback::{BoxedError, Fallback};
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use zebra_chain::{
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primitives::{
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ed25519::{self, VerificationKeyBytes},
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Groth16Proof,
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},
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sapling::{Output, PerSpendAnchor, Spend},
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sprout::{JoinSplit, Nullifier, RandomSeed},
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};
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mod params;
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#[cfg(test)]
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mod tests;
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#[cfg(test)]
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mod vectors;
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pub use params::{Groth16Parameters, GROTH16_PARAMETERS};
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use crate::error::TransactionError;
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/// Global batch verification context for Groth16 proofs of Spend statements.
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///
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/// This service transparently batches contemporaneous proof verifications,
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/// handling batch failures by falling back to individual verification.
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///
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/// Note that making a `Service` call requires mutable access to the service, so
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/// you should call `.clone()` on the global handle to create a local, mutable
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/// handle.
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pub static SPEND_VERIFIER: Lazy<
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Fallback<Batch<Verifier, Item>, ServiceFn<fn(Item) -> Ready<Result<(), VerificationError>>>>,
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> = Lazy::new(|| {
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Fallback::new(
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Batch::new(
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Verifier::new(&GROTH16_PARAMETERS.sapling.spend.vk),
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super::MAX_BATCH_SIZE,
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super::MAX_BATCH_LATENCY,
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),
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// We want to fallback to individual verification if batch verification
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// fails, so we need a Service to use. The obvious way to do this would
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// be to write a closure that returns an async block. But because we
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// have to specify the type of a static, we need to be able to write the
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// type of the closure and its return value, and both closures and async
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// blocks have eldritch types whose names cannot be written. So instead,
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// we use a Ready to avoid an async block and cast the closure to a
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// function (which is possible because it doesn't capture any state).
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tower::service_fn(
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(|item: Item| {
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ready(item.verify_single(&GROTH16_PARAMETERS.sapling.spend_prepared_verifying_key))
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}) as fn(_) -> _,
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),
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)
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});
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/// Global batch verification context for Groth16 proofs of Output statements.
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///
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/// This service transparently batches contemporaneous proof verifications,
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/// handling batch failures by falling back to individual verification.
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///
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/// Note that making a `Service` call requires mutable access to the service, so
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/// you should call `.clone()` on the global handle to create a local, mutable
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/// handle.
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pub static OUTPUT_VERIFIER: Lazy<
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Fallback<Batch<Verifier, Item>, ServiceFn<fn(Item) -> Ready<Result<(), VerificationError>>>>,
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> = Lazy::new(|| {
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Fallback::new(
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Batch::new(
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Verifier::new(&GROTH16_PARAMETERS.sapling.output.vk),
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super::MAX_BATCH_SIZE,
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super::MAX_BATCH_LATENCY,
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),
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// We want to fallback to individual verification if batch verification
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// fails, so we need a Service to use. The obvious way to do this would
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// be to write a closure that returns an async block. But because we
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// have to specify the type of a static, we need to be able to write the
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// type of the closure and its return value, and both closures and async
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// blocks have eldritch types whose names cannot be written. So instead,
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// we use a Ready to avoid an async block and cast the closure to a
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// function (which is possible because it doesn't capture any state).
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tower::service_fn(
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(|item: Item| {
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ready(item.verify_single(&GROTH16_PARAMETERS.sapling.output_prepared_verifying_key))
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}) as fn(_) -> _,
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),
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)
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});
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/// Global batch verification context for Groth16 proofs of JoinSplit statements.
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///
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/// This service does not yet batch verifications, see
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/// https://github.com/ZcashFoundation/zebra/issues/3127
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///
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/// Note that making a `Service` call requires mutable access to the service, so
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/// you should call `.clone()` on the global handle to create a local, mutable
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/// handle.
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pub static JOINSPLIT_VERIFIER: Lazy<ServiceFn<fn(Item) -> Ready<Result<(), BoxedError>>>> =
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Lazy::new(|| {
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// We need a Service to use. The obvious way to do this would
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// be to write a closure that returns an async block. But because we
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// have to specify the type of a static, we need to be able to write the
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// type of the closure and its return value, and both closures and async
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// blocks have eldritch types whose names cannot be written. So instead,
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// we use a Ready to avoid an async block and cast the closure to a
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// function (which is possible because it doesn't capture any state).
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tower::service_fn(
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(|item: Item| {
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// Workaround bug in `bellman::VerificationError` fmt::Display
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// implementation https://github.com/zkcrypto/bellman/pull/77
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#[allow(deprecated)]
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ready(
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item.verify_single(&GROTH16_PARAMETERS.sprout.joinsplit_prepared_verifying_key)
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// When that is fixed, change to `e.to_string()`
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.map_err(|e| TransactionError::Groth16(e.description().to_string()))
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.map_err(tower_fallback::BoxedError::from),
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)
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}) as fn(_) -> _,
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)
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});
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/// A Groth16 Description (JoinSplit, Spend, or Output) with a Groth16 proof
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/// and its inputs encoded as scalars.
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pub trait Description {
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/// The Groth16 proof of this description.
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fn proof(&self) -> &Groth16Proof;
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/// The primary inputs for this proof, encoded as [`jubjub::Fq`] scalars.
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fn primary_inputs(&self) -> Vec<jubjub::Fq>;
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}
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impl Description for Spend<PerSpendAnchor> {
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/// Encodes the primary input for the Sapling Spend proof statement as 7 Bls12_381 base
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/// field elements, to match [`bellman::groth16::verify_proof`] (the starting fixed element
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/// `1` is filled in by [`bellman`].
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///
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/// NB: jubjub::Fq is a type alias for bls12_381::Scalar.
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///
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/// <https://zips.z.cash/protocol/protocol.pdf#cctsaplingspend>
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fn primary_inputs(&self) -> Vec<jubjub::Fq> {
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let mut inputs = vec![];
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let rk_affine = jubjub::AffinePoint::from_bytes(self.rk.clone().into()).unwrap();
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inputs.push(rk_affine.get_u());
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inputs.push(rk_affine.get_v());
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let cv_affine = jubjub::AffinePoint::from(self.cv);
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inputs.push(cv_affine.get_u());
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inputs.push(cv_affine.get_v());
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// TODO: V4 only
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inputs.push(jubjub::Fq::from_bytes(&self.per_spend_anchor.into()).unwrap());
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let nullifier_limbs: [jubjub::Fq; 2] = self.nullifier.into();
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inputs.push(nullifier_limbs[0]);
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inputs.push(nullifier_limbs[1]);
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inputs
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}
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fn proof(&self) -> &Groth16Proof {
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&self.zkproof
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}
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}
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impl Description for Output {
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/// Encodes the primary input for the Sapling Output proof statement as 5 Bls12_381 base
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/// field elements, to match [`bellman::groth16::verify_proof`] (the starting fixed element
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/// `1` is filled in by [`bellman`].
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///
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/// NB: [`jubjub::Fq`] is a type alias for [`bls12_381::Scalar`].
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///
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/// <https://zips.z.cash/protocol/protocol.pdf#cctsaplingoutput>
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fn primary_inputs(&self) -> Vec<jubjub::Fq> {
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let mut inputs = vec![];
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let cv_affine = jubjub::AffinePoint::from(self.cv);
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inputs.push(cv_affine.get_u());
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inputs.push(cv_affine.get_v());
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let epk_affine = jubjub::AffinePoint::from_bytes(self.ephemeral_key.into()).unwrap();
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inputs.push(epk_affine.get_u());
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inputs.push(epk_affine.get_v());
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inputs.push(self.cm_u);
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inputs
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}
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fn proof(&self) -> &Groth16Proof {
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&self.zkproof
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}
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}
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/// Compute the [h_{Sig} hash function][1] which is used in JoinSplit descriptions.
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///
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/// `random_seed`: the random seed from the JoinSplit description.
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/// `nf1`: the first nullifier from the JoinSplit description.
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/// `nf2`: the second nullifier from the JoinSplit description.
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/// `joinsplit_pub_key`: the JoinSplit public validation key from the transaction.
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///
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/// [1]: https://zips.z.cash/protocol/protocol.pdf#hsigcrh
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pub(super) fn h_sig(
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random_seed: &RandomSeed,
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nf1: &Nullifier,
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nf2: &Nullifier,
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joinsplit_pub_key: &VerificationKeyBytes,
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) -> [u8; 32] {
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let h_sig: [u8; 32] = blake2b_simd::Params::new()
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.hash_length(32)
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.personal(b"ZcashComputehSig")
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.to_state()
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.update(&(<[u8; 32]>::from(random_seed))[..])
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.update(&(<[u8; 32]>::from(nf1))[..])
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.update(&(<[u8; 32]>::from(nf2))[..])
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.update(joinsplit_pub_key.as_ref())
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.finalize()
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.as_bytes()
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.try_into()
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.expect("32 byte array");
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h_sig
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}
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impl Description for (&JoinSplit<Groth16Proof>, &ed25519::VerificationKeyBytes) {
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/// Encodes the primary input for the JoinSplit proof statement as Bls12_381 base
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/// field elements, to match [`bellman::groth16::verify_proof()`].
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///
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/// NB: [`jubjub::Fq`] is a type alias for [`bls12_381::Scalar`].
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///
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/// `joinsplit_pub_key`: the JoinSplit public validation key for this JoinSplit, from
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/// the transaction. (All JoinSplits in a transaction share the same validation key.)
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///
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/// This is not yet officially documented; see the reference implementation:
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/// https://github.com/zcash/librustzcash/blob/0ec7f97c976d55e1a194a37b27f247e8887fca1d/zcash_proofs/src/sprout.rs#L152-L166
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/// <https://zips.z.cash/protocol/protocol.pdf#joinsplitdesc>
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fn primary_inputs(&self) -> Vec<jubjub::Fq> {
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let (joinsplit, joinsplit_pub_key) = self;
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let rt: [u8; 32] = joinsplit.anchor.into();
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let mac1: [u8; 32] = (&joinsplit.vmacs[0]).into();
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let mac2: [u8; 32] = (&joinsplit.vmacs[1]).into();
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let nf1: [u8; 32] = (&joinsplit.nullifiers[0]).into();
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let nf2: [u8; 32] = (&joinsplit.nullifiers[1]).into();
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let cm1: [u8; 32] = (&joinsplit.commitments[0]).into();
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let cm2: [u8; 32] = (&joinsplit.commitments[1]).into();
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let vpub_old = joinsplit.vpub_old.to_bytes();
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let vpub_new = joinsplit.vpub_new.to_bytes();
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let h_sig = h_sig(
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&joinsplit.random_seed,
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&joinsplit.nullifiers[0],
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&joinsplit.nullifiers[1],
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joinsplit_pub_key,
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);
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// Prepare the public input for the verifier
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let mut public_input = Vec::with_capacity((32 * 8) + (8 * 2));
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public_input.extend(rt);
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public_input.extend(h_sig);
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public_input.extend(nf1);
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public_input.extend(mac1);
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public_input.extend(nf2);
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public_input.extend(mac2);
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public_input.extend(cm1);
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public_input.extend(cm2);
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public_input.extend(vpub_old);
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public_input.extend(vpub_new);
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let public_input = multipack::bytes_to_bits(&public_input);
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multipack::compute_multipacking(&public_input)
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}
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fn proof(&self) -> &Groth16Proof {
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&self.0.zkproof
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}
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}
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/// A Groth16 verification item, used as the request type of the service.
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pub type Item = batch::Item<Bls12>;
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/// A wrapper to allow a TryFrom blanket implementation of the [`Description`]
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/// trait for the [`Item`] struct.
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/// See https://github.com/rust-lang/rust/issues/50133 for more details.
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pub struct DescriptionWrapper<T>(pub T);
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impl<T> TryFrom<DescriptionWrapper<&T>> for Item
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where
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T: Description,
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{
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type Error = TransactionError;
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fn try_from(input: DescriptionWrapper<&T>) -> Result<Self, Self::Error> {
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// # Consensus
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//
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// > Elements of a JoinSplit description MUST have the types given above
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//
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// https://zips.z.cash/protocol/protocol.pdf#joinsplitdesc
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//
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// This validates the 𝜋_{ZKJoinSplit} element. In #3179 we plan to validate
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// during deserialization, see [`JoinSplit::zcash_deserialize`].
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Ok(Item::from((
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bellman::groth16::Proof::read(&input.0.proof().0[..])
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.map_err(|e| TransactionError::MalformedGroth16(e.to_string()))?,
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input.0.primary_inputs(),
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)))
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}
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}
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/// Groth16 signature verifier implementation
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///
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/// This is the core implementation for the batch verification logic of the groth
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/// verifier. It handles batching incoming requests, driving batches to
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/// completion, and reporting results.
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pub struct Verifier {
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batch: batch::Verifier<Bls12>,
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// Making this 'static makes managing lifetimes much easier.
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vk: &'static VerifyingKey<Bls12>,
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/// Broadcast sender used to send the result of a batch verification to each
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/// request source in the batch.
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tx: Sender<Result<(), VerificationError>>,
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}
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impl Verifier {
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fn new(vk: &'static VerifyingKey<Bls12>) -> Self {
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let batch = batch::Verifier::default();
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let (tx, _) = channel(super::BROADCAST_BUFFER_SIZE);
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Self { batch, vk, tx }
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}
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}
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impl fmt::Debug for Verifier {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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let name = "Verifier";
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f.debug_struct(name)
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.field("batch", &"..")
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.field("vk", &"..")
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.field("tx", &self.tx)
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.finish()
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}
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}
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impl Service<BatchControl<Item>> for Verifier {
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type Response = ();
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type Error = VerificationError;
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type Future = Pin<Box<dyn Future<Output = Result<(), VerificationError>> + Send + 'static>>;
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fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
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Poll::Ready(Ok(()))
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}
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fn call(&mut self, req: BatchControl<Item>) -> Self::Future {
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match req {
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BatchControl::Item(item) => {
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tracing::trace!("got item");
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self.batch.queue(item);
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let mut rx = self.tx.subscribe();
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Box::pin(async move {
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match rx.recv().await {
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Ok(result) => {
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if result.is_ok() {
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tracing::trace!(?result, "verified groth16 proof");
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metrics::counter!("proofs.groth16.verified", 1);
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} else {
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tracing::trace!(?result, "invalid groth16 proof");
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metrics::counter!("proofs.groth16.invalid", 1);
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}
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result
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}
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Err(RecvError::Lagged(_)) => {
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tracing::error!(
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"missed channel updates, BROADCAST_BUFFER_SIZE is too low!!"
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);
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Err(VerificationError::InvalidProof)
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}
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Err(RecvError::Closed) => panic!("verifier was dropped without flushing"),
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}
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})
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}
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BatchControl::Flush => {
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tracing::trace!("got flush command");
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let batch = mem::take(&mut self.batch);
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let _ = self.tx.send(batch.verify(thread_rng(), self.vk));
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Box::pin(async { Ok(()) })
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}
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}
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}
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}
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impl Drop for Verifier {
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fn drop(&mut self) {
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// We need to flush the current batch in case there are still any pending futures.
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let batch = mem::take(&mut self.batch);
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let _ = self.tx.send(batch.verify(thread_rng(), self.vk));
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}
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}
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