zcash_primitives: Implement batched trial decryption optimisation

zcash_primitives/benches/note_decryption.rs

@@ -1,14 +1,17 @@
-use criterion::{criterion_group, criterion_main, Criterion};
+use std::iter;
+
+use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion, Throughput};
 use ff::Field;
 use group::GroupEncoding;
 use rand_core::OsRng;
+use zcash_note_encryption::batch;
 use zcash_primitives::{
     consensus::{NetworkUpgrade::Canopy, Parameters, TestNetwork, TEST_NETWORK},
     memo::MemoBytes,
     sapling::{
         note_encryption::{
             sapling_note_encryption, try_sapling_compact_note_decryption,
-            try_sapling_note_decryption,
+            try_sapling_note_decryption, SaplingDomain,
         },
         util::generate_random_rseed,
         Diversifier, PaymentAddress, SaplingIvk, ValueCommitment,
@@ -64,30 +67,77 @@ fn bench_note_decryption(c: &mut Criterion) {
         }
     };
 
-    let mut group = c.benchmark_group("sapling-note-decryption");
+    {
+        let mut group = c.benchmark_group("sapling-note-decryption");
+        group.throughput(Throughput::Elements(1));
 
-    group.bench_function("valid", |b| {
-        b.iter(|| try_sapling_note_decryption(&TEST_NETWORK, height, &valid_ivk, &output).unwrap())
-    });
+        group.bench_function("valid", |b| {
+            b.iter(|| {
+                try_sapling_note_decryption(&TEST_NETWORK, height, &valid_ivk, &output).unwrap()
+            })
+        });
 
-    group.bench_function("invalid", |b| {
-        b.iter(|| try_sapling_note_decryption(&TEST_NETWORK, height, &invalid_ivk, &output))
-    });
+        group.bench_function("invalid", |b| {
+            b.iter(|| try_sapling_note_decryption(&TEST_NETWORK, height, &invalid_ivk, &output))
+        });
 
-    let compact = CompactOutputDescription::from(output);
+        let compact = CompactOutputDescription::from(output.clone());
 
-    group.bench_function("compact-valid", |b| {
-        b.iter(|| {
-            try_sapling_compact_note_decryption(&TEST_NETWORK, height, &valid_ivk, &compact)
-                .unwrap()
-        })
-    });
+        group.bench_function("compact-valid", |b| {
+            b.iter(|| {
+                try_sapling_compact_note_decryption(&TEST_NETWORK, height, &valid_ivk, &compact)
+                    .unwrap()
+            })
+        });
 
-    group.bench_function("compact-invalid", |b| {
-        b.iter(|| {
-            try_sapling_compact_note_decryption(&TEST_NETWORK, height, &invalid_ivk, &compact)
-        })
-    });
+        group.bench_function("compact-invalid", |b| {
+            b.iter(|| {
+                try_sapling_compact_note_decryption(&TEST_NETWORK, height, &invalid_ivk, &compact)
+            })
+        });
+    }
+
+    {
+        let valid_ivks = vec![valid_ivk];
+        let invalid_ivks = vec![invalid_ivk];
+
+        // We benchmark with one IVK so the overall batch size is equal to the number of
+        // outputs.
+        let size = 10;
+        let outputs: Vec<_> = iter::repeat(output)
+            .take(size)
+            .map(|output| {
+                (
+                    SaplingDomain::for_height(TEST_NETWORK.clone(), height),
+                    output,
+                )
+            })
+            .collect();
+
+        let mut group = c.benchmark_group("sapling-batch-note-decryption");
+        group.throughput(Throughput::Elements(size as u64));
+
+        group.bench_function(BenchmarkId::new("valid", size), |b| {
+            b.iter(|| batch::try_note_decryption(&valid_ivks, &outputs))
+        });
+
+        group.bench_function(BenchmarkId::new("invalid", size), |b| {
+            b.iter(|| batch::try_note_decryption(&invalid_ivks, &outputs))
+        });
+
+        let compact: Vec<_> = outputs
+            .into_iter()
+            .map(|(domain, output)| (domain, CompactOutputDescription::from(output.clone())))
+            .collect();
+
+        group.bench_function(BenchmarkId::new("compact-valid", size), |b| {
+            b.iter(|| batch::try_compact_note_decryption(&valid_ivks, &compact))
+        });
+
+        group.bench_function(BenchmarkId::new("compact-invalid", size), |b| {
+            b.iter(|| batch::try_compact_note_decryption(&invalid_ivks, &compact))
+        });
+    }
 }
 
 #[cfg(unix)]

zcash_primitives/src/sapling/note_encryption.rs

@@ -3,6 +3,7 @@ use blake2b_simd::{Hash as Blake2bHash, Params as Blake2bParams};
 use byteorder::{LittleEndian, WriteBytesExt};
 use ff::PrimeField;
 use group::{cofactor::CofactorGroup, GroupEncoding};
+use jubjub::{AffinePoint, ExtendedPoint};
 use rand_core::RngCore;
 use std::convert::TryInto;
 
@@ -119,6 +120,12 @@ pub struct SaplingDomain<P: consensus::Parameters> {
     height: BlockHeight,
 }
 
+impl<P: consensus::Parameters> SaplingDomain<P> {
+    pub fn for_height(params: P, height: BlockHeight) -> Self {
+        Self { params, height }
+    }
+}
+
 impl<P: consensus::Parameters> Domain for SaplingDomain<P> {
     type EphemeralSecretKey = jubjub::Scalar;
     // It is acceptable for this to be a point because we enforce by consensus that
@@ -178,6 +185,37 @@ impl<P: consensus::Parameters> Domain for SaplingDomain<P> {
         kdf_sapling(dhsecret, epk)
     }
 
+    fn batch_kdf<'a>(
+        items: impl Iterator<Item = (Option<Self::SharedSecret>, &'a EphemeralKeyBytes)>,
+    ) -> Vec<Option<Self::SymmetricKey>> {
+        let (shared_secrets, ephemeral_keys): (Vec<_>, Vec<_>) = items.unzip();
+
+        let secrets: Vec<_> = shared_secrets
+            .iter()
+            .filter_map(|s| s.map(ExtendedPoint::from))
+            .collect();
+        let mut secrets_affine = vec![AffinePoint::identity(); shared_secrets.len()];
+        group::Curve::batch_normalize(&secrets, &mut secrets_affine);
+
+        let mut secrets_affine = secrets_affine.into_iter();
+        shared_secrets
+            .into_iter()
+            .map(|s| s.and_then(|_| secrets_affine.next()))
+            .zip(ephemeral_keys.into_iter())
+            .map(|(secret, ephemeral_key)| {
+                secret.map(|dhsecret| {
+                    Blake2bParams::new()
+                        .hash_length(32)
+                        .personal(KDF_SAPLING_PERSONALIZATION)
+                        .to_state()
+                        .update(&dhsecret.to_bytes())
+                        .update(ephemeral_key.as_ref())
+                        .finalize()
+                })
+            })
+            .collect()
+    }
+
     fn note_plaintext_bytes(
         note: &Self::Note,
         to: &Self::Recipient,
@@ -436,7 +474,7 @@ mod tests {
     use std::convert::TryInto;
 
     use zcash_note_encryption::{
-        EphemeralKeyBytes, NoteEncryption, OutgoingCipherKey, ENC_CIPHERTEXT_SIZE,
+        batch, EphemeralKeyBytes, NoteEncryption, OutgoingCipherKey, ENC_CIPHERTEXT_SIZE,
         NOTE_PLAINTEXT_SIZE, OUT_CIPHERTEXT_SIZE, OUT_PLAINTEXT_SIZE,
     };
 
@@ -1340,6 +1378,37 @@ mod tests {
                 None => panic!("Output recovery failed"),
             }
 
+            match &batch::try_note_decryption(
+                &[ivk.clone()],
+                &[(
+                    SaplingDomain::for_height(TEST_NETWORK, height),
+                    output.clone(),
+                )],
+            )[..]
+            {
+                [Some((decrypted_note, decrypted_to, decrypted_memo))] => {
+                    assert_eq!(decrypted_note, &note);
+                    assert_eq!(decrypted_to, &to);
+                    assert_eq!(&decrypted_memo.as_array()[..], &tv.memo[..]);
+                }
+                _ => panic!("Note decryption failed"),
+            }
+
+            match &batch::try_compact_note_decryption(
+                &[ivk.clone()],
+                &[(
+                    SaplingDomain::for_height(TEST_NETWORK, height),
+                    CompactOutputDescription::from(output.clone()),
+                )],
+            )[..]
+            {
+                [Some((decrypted_note, decrypted_to))] => {
+                    assert_eq!(decrypted_note, &note);
+                    assert_eq!(decrypted_to, &to);
+                }
+                _ => panic!("Note decryption failed"),
+            }
+
             //
             // Test encryption
             //
@@ -1359,4 +1428,29 @@ mod tests {
             );
         }
     }
+
+    #[test]
+    fn batching() {
+        let mut rng = OsRng;
+        let height = TEST_NETWORK.activation_height(Canopy).unwrap();
+
+        // Test batch trial-decryption with multiple IVKs and outputs.
+        let invalid_ivk = SaplingIvk(jubjub::Fr::random(rng));
+        let valid_ivk = SaplingIvk(jubjub::Fr::random(rng));
+        let outputs: Vec<_> = (0..10)
+            .map(|_| {
+                (
+                    SaplingDomain::for_height(TEST_NETWORK, height),
+                    random_enc_ciphertext_with(height, &valid_ivk, &mut rng).2,
+                )
+            })
+            .collect();
+
+        let res = batch::try_note_decryption(&[invalid_ivk, valid_ivk], &outputs);
+        assert_eq!(res.len(), 20);
+        assert_eq!(&res[..10], &vec![None; 10][..]);
+        for result in &res[10..] {
+            assert!(result.is_some());
+        }
+    }
 }