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zebra/zebra-consensus/src/primitives/groth16.rs

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//! Async Groth16 batch verifier service
use std::{
fmt,
future::Future,
mem,
pin::Pin,
task::{Context, Poll},
};
use bellman::{
gadgets::multipack,
groth16::{batch, PreparedVerifyingKey, VerifyingKey},
VerificationError,
};
use bls12_381::Bls12;
use futures::{future::BoxFuture, FutureExt};
use once_cell::sync::Lazy;
use rand::thread_rng;
use tokio::sync::watch;
use tower::{util::ServiceFn, Service};
use tower_batch_control::{Batch, BatchControl};
use tower_fallback::{BoxedError, Fallback};
use zebra_chain::{
primitives::{
ed25519::{self, VerificationKeyBytes},
Groth16Proof,
},
sapling::{Output, PerSpendAnchor, Spend},
sprout::{JoinSplit, Nullifier, RandomSeed},
};
use crate::BoxError;
use super::{spawn_fifo, spawn_fifo_and_convert};
mod params;
#[cfg(test)]
mod tests;
#[cfg(test)]
mod vectors;
pub use params::{Groth16Parameters, GROTH16_PARAMETERS};
use crate::error::TransactionError;
/// The type of the batch verifier.
type BatchVerifier = batch::Verifier<Bls12>;
/// The type of verification results.
type VerifyResult = Result<(), VerificationError>;
/// The type of the batch sender channel.
type Sender = watch::Sender<Option<VerifyResult>>;
/// The type of the batch item.
/// This is a Groth16 verification item.
pub type Item = batch::Item<Bls12>;
/// The type of a raw verifying key.
/// This is the key used to verify batches.
pub type BatchVerifyingKey = VerifyingKey<Bls12>;
/// The type of a prepared verifying key.
/// This is the key used to verify individual items.
pub type ItemVerifyingKey = PreparedVerifyingKey<Bls12>;
/// Global batch verification context for Groth16 proofs of Spend statements.
///
/// This service transparently batches contemporaneous proof verifications,
/// handling batch failures by falling back to individual verification.
///
/// Note that making a `Service` call requires mutable access to the service, so
/// you should call `.clone()` on the global handle to create a local, mutable
/// handle.
pub static SPEND_VERIFIER: Lazy<
Fallback<
Batch<Verifier, Item>,
ServiceFn<fn(Item) -> BoxFuture<'static, Result<(), BoxError>>>,
>,
> = Lazy::new(|| {
Fallback::new(
Batch::new(
Verifier::new(&GROTH16_PARAMETERS.sapling.spend.vk),
super::MAX_BATCH_SIZE,
None,
super::MAX_BATCH_LATENCY,
),
// We want to fallback to individual verification if batch verification fails,
// so we need a Service to use.
//
// Because we have to specify the type of a static, we need to be able to
// write the type of the closure and its return value. But both closures and
// async blocks have unnameable types. So instead we cast the closure to a function
// (which is possible because it doesn't capture any state), and use a BoxFuture
// to erase the result type.
// (We can't use BoxCloneService to erase the service type, because it is !Sync.)
tower::service_fn(
(|item: Item| {
Verifier::verify_single_spawning(
item,
&GROTH16_PARAMETERS.sapling.spend_prepared_verifying_key,
)
.boxed()
}) as fn(_) -> _,
),
)
});
/// Global batch verification context for Groth16 proofs of Output statements.
///
/// This service transparently batches contemporaneous proof verifications,
/// handling batch failures by falling back to individual verification.
///
/// Note that making a `Service` call requires mutable access to the service, so
/// you should call `.clone()` on the global handle to create a local, mutable
/// handle.
pub static OUTPUT_VERIFIER: Lazy<
Fallback<
Batch<Verifier, Item>,
ServiceFn<fn(Item) -> BoxFuture<'static, Result<(), BoxError>>>,
>,
> = Lazy::new(|| {
Fallback::new(
Batch::new(
Verifier::new(&GROTH16_PARAMETERS.sapling.output.vk),
super::MAX_BATCH_SIZE,
None,
super::MAX_BATCH_LATENCY,
),
// We want to fallback to individual verification if batch verification
// fails, so we need a Service to use.
//
// See the note on [`SPEND_VERIFIER`] for details.
tower::service_fn(
(|item: Item| {
Verifier::verify_single_spawning(
item,
&GROTH16_PARAMETERS.sapling.output_prepared_verifying_key,
)
.boxed()
}) as fn(_) -> _,
),
)
});
/// Global batch verification context for Groth16 proofs of JoinSplit statements.
///
/// This service does not yet batch verifications, see
/// <https://github.com/ZcashFoundation/zebra/issues/3127>
///
/// Note that making a `Service` call requires mutable access to the service, so
/// you should call `.clone()` on the global handle to create a local, mutable
/// handle.
pub static JOINSPLIT_VERIFIER: Lazy<
ServiceFn<fn(Item) -> BoxFuture<'static, Result<(), BoxedError>>>,
> = Lazy::new(|| {
// We just need a Service to use: there is no batch verification for JoinSplits.
//
// See the note on [`SPEND_VERIFIER`] for details.
tower::service_fn(
(|item: Item| {
Verifier::verify_single_spawning(
item,
&GROTH16_PARAMETERS.sprout.joinsplit_prepared_verifying_key,
)
.map(|result| {
result
.map_err(|e| TransactionError::Groth16(e.to_string()))
.map_err(tower_fallback::BoxedError::from)
})
.boxed()
}) as fn(_) -> _,
)
});
/// A Groth16 Description (JoinSplit, Spend, or Output) with a Groth16 proof
/// and its inputs encoded as scalars.
pub trait Description {
/// The Groth16 proof of this description.
fn proof(&self) -> &Groth16Proof;
/// The primary inputs for this proof, encoded as [`jubjub::Fq`] scalars.
fn primary_inputs(&self) -> Vec<jubjub::Fq>;
}
impl Description for Spend<PerSpendAnchor> {
/// Encodes the primary input for the Sapling Spend proof statement as 7 Bls12_381 base
/// field elements, to match [`bellman::groth16::verify_proof`] (the starting fixed element
/// `1` is filled in by [`bellman`].
///
/// NB: jubjub::Fq is a type alias for bls12_381::Scalar.
///
/// <https://zips.z.cash/protocol/protocol.pdf#cctsaplingspend>
fn primary_inputs(&self) -> Vec<jubjub::Fq> {
let mut inputs = vec![];
let rk_affine = jubjub::AffinePoint::from_bytes(self.rk.clone().into()).unwrap();
inputs.push(rk_affine.get_u());
inputs.push(rk_affine.get_v());
let cv_affine = jubjub::AffinePoint::from(self.cv);
inputs.push(cv_affine.get_u());
inputs.push(cv_affine.get_v());
// TODO: V4 only
inputs.push(jubjub::Fq::from_bytes(&self.per_spend_anchor.into()).unwrap());
let nullifier_limbs: [jubjub::Fq; 2] = self.nullifier.into();
inputs.push(nullifier_limbs[0]);
inputs.push(nullifier_limbs[1]);
inputs
}
fn proof(&self) -> &Groth16Proof {
&self.zkproof
}
}
impl Description for Output {
/// Encodes the primary input for the Sapling Output proof statement as 5 Bls12_381 base
/// field elements, to match [`bellman::groth16::verify_proof`] (the starting fixed element
/// `1` is filled in by [`bellman`].
///
/// NB: [`jubjub::Fq`] is a type alias for [`bls12_381::Scalar`].
///
/// <https://zips.z.cash/protocol/protocol.pdf#cctsaplingoutput>
fn primary_inputs(&self) -> Vec<jubjub::Fq> {
let mut inputs = vec![];
let cv_affine = jubjub::AffinePoint::from(self.cv);
inputs.push(cv_affine.get_u());
inputs.push(cv_affine.get_v());
let epk_affine = jubjub::AffinePoint::from_bytes(self.ephemeral_key.into()).unwrap();
inputs.push(epk_affine.get_u());
inputs.push(epk_affine.get_v());
inputs.push(self.cm_u);
inputs
}
fn proof(&self) -> &Groth16Proof {
&self.zkproof
}
}
/// Compute the [h_{Sig} hash function][1] which is used in JoinSplit descriptions.
///
/// `random_seed`: the random seed from the JoinSplit description.
/// `nf1`: the first nullifier from the JoinSplit description.
/// `nf2`: the second nullifier from the JoinSplit description.
/// `joinsplit_pub_key`: the JoinSplit public validation key from the transaction.
///
/// [1]: https://zips.z.cash/protocol/protocol.pdf#hsigcrh
pub(super) fn h_sig(
random_seed: &RandomSeed,
nf1: &Nullifier,
nf2: &Nullifier,
joinsplit_pub_key: &VerificationKeyBytes,
) -> [u8; 32] {
let h_sig: [u8; 32] = blake2b_simd::Params::new()
.hash_length(32)
.personal(b"ZcashComputehSig")
.to_state()
.update(&(<[u8; 32]>::from(random_seed))[..])
.update(&(<[u8; 32]>::from(nf1))[..])
.update(&(<[u8; 32]>::from(nf2))[..])
.update(joinsplit_pub_key.as_ref())
.finalize()
.as_bytes()
.try_into()
.expect("32 byte array");
h_sig
}
impl Description for (&JoinSplit<Groth16Proof>, &ed25519::VerificationKeyBytes) {
/// Encodes the primary input for the JoinSplit proof statement as Bls12_381 base
/// field elements, to match [`bellman::groth16::verify_proof()`].
///
/// NB: [`jubjub::Fq`] is a type alias for [`bls12_381::Scalar`].
///
/// `joinsplit_pub_key`: the JoinSplit public validation key for this JoinSplit, from
/// the transaction. (All JoinSplits in a transaction share the same validation key.)
///
/// This is not yet officially documented; see the reference implementation:
/// <https://github.com/zcash/librustzcash/blob/0ec7f97c976d55e1a194a37b27f247e8887fca1d/zcash_proofs/src/sprout.rs#L152-L166>
/// <https://zips.z.cash/protocol/protocol.pdf#joinsplitdesc>
//
// The borrows are actually needed to avoid taking ownership
#[allow(clippy::needless_borrow)]
fn primary_inputs(&self) -> Vec<jubjub::Fq> {
let (joinsplit, joinsplit_pub_key) = self;
let rt: [u8; 32] = joinsplit.anchor.into();
let mac1: [u8; 32] = (&joinsplit.vmacs[0]).into();
let mac2: [u8; 32] = (&joinsplit.vmacs[1]).into();
let nf1: [u8; 32] = (&joinsplit.nullifiers[0]).into();
let nf2: [u8; 32] = (&joinsplit.nullifiers[1]).into();
let cm1: [u8; 32] = (&joinsplit.commitments[0]).into();
let cm2: [u8; 32] = (&joinsplit.commitments[1]).into();
let vpub_old = joinsplit.vpub_old.to_bytes();
let vpub_new = joinsplit.vpub_new.to_bytes();
let h_sig = h_sig(
&joinsplit.random_seed,
&joinsplit.nullifiers[0],
&joinsplit.nullifiers[1],
joinsplit_pub_key,
);
// Prepare the public input for the verifier
let mut public_input = Vec::with_capacity((32 * 8) + (8 * 2));
public_input.extend(rt);
public_input.extend(h_sig);
public_input.extend(nf1);
public_input.extend(mac1);
public_input.extend(nf2);
public_input.extend(mac2);
public_input.extend(cm1);
public_input.extend(cm2);
public_input.extend(vpub_old);
public_input.extend(vpub_new);
let public_input = multipack::bytes_to_bits(&public_input);
multipack::compute_multipacking(&public_input)
}
fn proof(&self) -> &Groth16Proof {
&self.0.zkproof
}
}
/// A wrapper to allow a TryFrom blanket implementation of the [`Description`]
/// trait for the [`Item`] struct.
/// See <https://github.com/rust-lang/rust/issues/50133> for more details.
pub struct DescriptionWrapper<T>(pub T);
impl<T> TryFrom<DescriptionWrapper<&T>> for Item
where
T: Description,
{
type Error = TransactionError;
fn try_from(input: DescriptionWrapper<&T>) -> Result<Self, Self::Error> {
// # Consensus
//
// > Elements of a JoinSplit description MUST have the types given above
//
// https://zips.z.cash/protocol/protocol.pdf#joinsplitdesc
//
// This validates the 𝜋_{ZKJoinSplit} element. In #3179 we plan to validate
// during deserialization, see [`JoinSplit::zcash_deserialize`].
Ok(Item::from((
bellman::groth16::Proof::read(&input.0.proof().0[..])
.map_err(|e| TransactionError::MalformedGroth16(e.to_string()))?,
input.0.primary_inputs(),
)))
}
}
/// Groth16 signature verifier implementation
///
/// This is the core implementation for the batch verification logic of the groth
/// verifier. It handles batching incoming requests, driving batches to
/// completion, and reporting results.
pub struct Verifier {
/// A batch verifier for groth16 proofs.
batch: BatchVerifier,
/// The proof verification key.
///
/// Making this 'static makes managing lifetimes much easier.
vk: &'static BatchVerifyingKey,
/// A channel for broadcasting the result of a batch to the futures for each batch item.
///
/// Each batch gets a newly created channel, so there is only ever one result sent per channel.
/// Tokio doesn't have a oneshot multi-consumer channel, so we use a watch channel.
tx: Sender,
}
impl Verifier {
/// Create and return a new verifier using the verification key `vk`.
fn new(vk: &'static BatchVerifyingKey) -> Self {
let batch = BatchVerifier::default();
let (tx, _) = watch::channel(None);
Self { batch, vk, tx }
}
/// Returns the batch verifier and channel sender from `self`,
/// replacing them with a new empty batch.
fn take(&mut self) -> (BatchVerifier, &'static BatchVerifyingKey, Sender) {
// Use a new verifier and channel for each batch.
let batch = mem::take(&mut self.batch);
let (tx, _) = watch::channel(None);
let tx = mem::replace(&mut self.tx, tx);
(batch, self.vk, tx)
}
/// Synchronously process the batch, and send the result using the channel sender.
/// This function blocks until the batch is completed.
fn verify(batch: BatchVerifier, vk: &'static BatchVerifyingKey, tx: Sender) {
let result = batch.verify(thread_rng(), vk);
let _ = tx.send(Some(result));
}
/// Flush the batch using a thread pool, and return the result via the channel.
/// This returns immediately, usually before the batch is completed.
fn flush_blocking(&mut self) {
let (batch, vk, tx) = self.take();
// Correctness: Do CPU-intensive work on a dedicated thread, to avoid blocking other futures.
//
// We don't care about execution order here, because this method is only called on drop.
tokio::task::block_in_place(|| rayon::spawn_fifo(|| Self::verify(batch, vk, tx)));
}
/// Flush the batch using a thread pool, and return the result via the channel.
/// This function returns a future that becomes ready when the batch is completed.
async fn flush_spawning(batch: BatchVerifier, vk: &'static BatchVerifyingKey, tx: Sender) {
// Correctness: Do CPU-intensive work on a dedicated thread, to avoid blocking other futures.
let _ = tx.send(
spawn_fifo(move || batch.verify(thread_rng(), vk))
.await
.ok(),
);
}
/// Verify a single item using a thread pool, and return the result.
async fn verify_single_spawning(
item: Item,
pvk: &'static ItemVerifyingKey,
) -> Result<(), BoxError> {
// Correctness: Do CPU-intensive work on a dedicated thread, to avoid blocking other futures.
spawn_fifo_and_convert(move || item.verify_single(pvk)).await
}
}
impl fmt::Debug for Verifier {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let name = "Verifier";
f.debug_struct(name)
.field("batch", &"..")
.field("vk", &"..")
.field("tx", &self.tx)
.finish()
}
}
impl Service<BatchControl<Item>> for Verifier {
type Response = ();
type Error = BoxError;
type Future = Pin<Box<dyn Future<Output = Result<(), BoxError>> + Send + 'static>>;
fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
Poll::Ready(Ok(()))
}
fn call(&mut self, req: BatchControl<Item>) -> Self::Future {
match req {
BatchControl::Item(item) => {
tracing::trace!("got item");
self.batch.queue(item);
let mut rx = self.tx.subscribe();
Box::pin(async move {
match rx.changed().await {
Ok(()) => {
// We use a new channel for each batch,
// so we always get the correct batch result here.
let result = rx
.borrow()
.as_ref()
.ok_or("threadpool unexpectedly dropped response channel sender. Is Zebra shutting down?")?
.clone();
if result.is_ok() {
tracing::trace!(?result, "verified groth16 proof");
metrics::counter!("proofs.groth16.verified").increment(1);
} else {
tracing::trace!(?result, "invalid groth16 proof");
metrics::counter!("proofs.groth16.invalid").increment(1);
}
result.map_err(BoxError::from)
}
Err(_recv_error) => panic!("verifier was dropped without flushing"),
}
})
}
BatchControl::Flush => {
tracing::trace!("got groth16 flush command");
let (batch, vk, tx) = self.take();
Box::pin(Self::flush_spawning(batch, vk, tx).map(Ok))
}
}
}
}
impl Drop for Verifier {
fn drop(&mut self) {
// We need to flush the current batch in case there are still any pending futures.
// This returns immediately, usually before the batch is completed.
self.flush_blocking()
}
}
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