223 lines
8.0 KiB
Rust
223 lines
8.0 KiB
Rust
//! Async Groth16 batch verifier service
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use std::{
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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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groth16::{batch, prepare_verifying_key, 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::Fallback;
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use zebra_chain::sapling::{Output, PerSpendAnchor, Spend};
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mod params;
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#[cfg(test)]
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mod tests;
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pub use params::{Groth16Parameters, GROTH16_PARAMETERS};
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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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> =
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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(&prepare_verifying_key(
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&GROTH16_PARAMETERS.sapling.spend.vk,
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)))
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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(&prepare_verifying_key(
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&GROTH16_PARAMETERS.sapling.output.vk,
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)))
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}) as fn(_) -> _,
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),
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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 workaround the missing `ServiceExt::map_err` method.
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pub struct ItemWrapper(Item);
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impl From<&Spend<PerSpendAnchor>> for ItemWrapper {
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fn from(spend: &Spend<PerSpendAnchor>) -> Self {
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Self(Item::from((
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bellman::groth16::Proof::read(&spend.zkproof.0[..]).unwrap(),
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spend.primary_inputs(),
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)))
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}
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}
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impl From<&Output> for ItemWrapper {
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fn from(output: &Output) -> Self {
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Self(Item::from((
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bellman::groth16::Proof::read(&output.zkproof.0[..]).unwrap(),
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output.primary_inputs(),
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)))
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}
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}
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impl From<ItemWrapper> for Item {
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fn from(item_wrapper: ItemWrapper) -> Self {
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item_wrapper.0
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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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