Add benchmark for note decryption

Cargo.toml

@@ -60,6 +60,10 @@ bench = false
 dev-graph = ["halo2/dev-graph", "plotters"]
 test-dependencies = ["proptest"]
 
+[[bench]]
+name = "note_decryption"
+harness = false
+
 [[bench]]
 name = "small"
 harness = false

benches/note_decryption.rs

@@ -0,0 +1,106 @@
+use criterion::{criterion_group, criterion_main, Criterion, Throughput};
+use orchard::{
+    builder::Builder,
+    bundle::Flags,
+    circuit::ProvingKey,
+    keys::{FullViewingKey, IncomingViewingKey, SpendingKey},
+    note_encryption::{CompactAction, OrchardDomain},
+    value::NoteValue,
+    Anchor, Bundle,
+};
+use rand::rngs::OsRng;
+use zcash_note_encryption::{try_compact_note_decryption, try_note_decryption};
+
+#[cfg(unix)]
+use pprof::criterion::{Output, PProfProfiler};
+
+fn bench_note_decryption(c: &mut Criterion) {
+    let rng = OsRng;
+    let pk = ProvingKey::build();
+
+    let fvk = FullViewingKey::from(&SpendingKey::from_bytes([7; 32]).unwrap());
+    let valid_ivk = IncomingViewingKey::from(&fvk);
+    let recipient = fvk.default_address();
+
+    // Compact actions don't have the full AEAD ciphertext, so ZIP 307 trial-decryption
+    // relies on an invalid ivk resulting in random noise for which the note commitment
+    // is invalid. However, in practice we still get early rejection:
+    // - The version byte will be invalid in 255/256 instances.
+    // - If the version byte is valid, one of either the note commitment check or the esk
+    //   check will be invalid, saving us at least one scalar mul.
+    //
+    // Our fixed (action, invalid ivk) tuple will always fall into a specific rejection
+    // case. In order to reflect the real behaviour in the benchmarks, we trial-decrypt
+    // with 1000 invalid ivks (each of which will result in a different uniformly-random
+    // plaintext); this is equivalent to trial-decrypting 1000 different actions with the
+    // same ivk, but is faster to set up.
+    let invalid_ivks: Vec<_> = (0u32..1000)
+        .map(|i| {
+            let mut sk = [0; 32];
+            sk[..4].copy_from_slice(&i.to_le_bytes());
+            IncomingViewingKey::from(&FullViewingKey::from(&SpendingKey::from_bytes(sk).unwrap()))
+        })
+        .collect();
+
+    let bundle = {
+        let mut builder = Builder::new(
+            Flags::from_parts(true, true),
+            Anchor::from_bytes([0; 32]).unwrap(),
+        );
+        builder
+            .add_recipient(None, recipient, NoteValue::from_raw(10), None)
+            .unwrap();
+        let bundle: Bundle<_, i64> = builder.build(rng).unwrap();
+        bundle
+            .create_proof(&pk)
+            .unwrap()
+            .apply_signatures(rng, [0; 32], &[])
+            .unwrap()
+    };
+    let action = bundle.actions().first();
+
+    let domain = OrchardDomain::for_action(action);
+
+    let compact = {
+        let mut group = c.benchmark_group("note-decryption");
+
+        group.bench_function("valid", |b| {
+            b.iter(|| try_note_decryption(&domain, &valid_ivk, action).unwrap())
+        });
+
+        // Non-compact actions will always early-reject at the same point: AEAD decryption.
+        group.bench_function("invalid", |b| {
+            b.iter(|| try_note_decryption(&domain, &invalid_ivks[0], action))
+        });
+
+        let compact = CompactAction::from(action);
+
+        group.bench_function("compact-valid", |b| {
+            b.iter(|| try_compact_note_decryption(&domain, &valid_ivk, &compact).unwrap())
+        });
+
+        compact
+    };
+
+    {
+        let mut group = c.benchmark_group("compact-note-decryption");
+        group.throughput(Throughput::Elements(invalid_ivks.len() as u64));
+        group.bench_function("invalid", |b| {
+            b.iter(|| {
+                for ivk in &invalid_ivks {
+                    try_compact_note_decryption(&domain, ivk, &compact);
+                }
+            })
+        });
+    }
+}
+
+#[cfg(unix)]
+criterion_group! {
+    name = benches;
+    config = Criterion::default().with_profiler(PProfProfiler::new(100, Output::Flamegraph(None)));
+    targets = bench_note_decryption
+}
+#[cfg(not(unix))]
+criterion_group!(benches, bench_note_decryption);
+criterion_main!(benches);