persistent signature cache for CI

Author: TomWambsgans

.github/workflows/rust.yml

@@ -48,8 +48,9 @@ jobs:
       - name: Cache benchmark signers
         uses: actions/cache@v4
         with:
-          path: target/signers-cache
+          path: .signers-cache
           key: benchmark-signers-${{ hashFiles('crates/xmss/**', 'crates/utils/**', 'crates/backend/**') }}
+          restore-keys: benchmark-signers-
       - name: Build
         run: cargo build --release --all --verbose
         env:
@@ -59,6 +60,7 @@ jobs:
         run: cargo test --release --all --verbose
         env:
           RUSTFLAGS: ${{ matrix.rustflags }}
+          SIGNERS_CACHE_DIR: ${{ github.workspace }}/.signers-cache
 
   cargo-clippy:
     runs-on: ubuntu-latest

Cargo.lock

@@ -62,6 +62,7 @@ rec_aggregation = { path = "crates/rec_aggregation" }
 backend = { path = "crates/backend" }
 
 # External
+sha3 = "0.11.0"
 clap = { version = "4.5.59", features = ["derive"] }
 rand = "0.10.0"
 rayon = "1.11.0"

Cargo.toml

@@ -14,6 +14,7 @@ backend.workspace = true
 serde.workspace = true
 lz4_flex.workspace = true
 postcard.workspace = true
+sha3.workspace = true
 
 [dev-dependencies]
 postcard.workspace = true

crates/xmss/Cargo.toml

@@ -1,15 +1,14 @@
+use backend::*;
+use rand::rngs::StdRng;
+use rand::{RngExt, SeedableRng};
+use serde::{Deserialize, Serialize};
+use sha3::{Digest, Sha3_256};
 use std::fs;
-use std::hash::{DefaultHasher, Hash, Hasher};
 use std::path::PathBuf;
 use std::sync::OnceLock;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::time::Instant;
 
-use backend::*;
-use rand::rngs::StdRng;
-use rand::{RngExt, SeedableRng};
-use serde::{Deserialize, Serialize};
-
 use crate::*;
 
 static SIGNERS_CACHE: OnceLock<Vec<(XmssPublicKey, XmssSignature)>> = OnceLock::new();
@@ -19,7 +18,7 @@ pub fn get_benchmark_signatures() -> &'static Vec<(XmssPublicKey, XmssSignature)
 }
 
 pub const BENCHMARK_SLOT: u32 = 111;
-pub const NUM_BENCHMARK_SIGNERS: usize = 10000;
+pub const NUM_BENCHMARK_SIGNERS: usize = 10_000;
 
 pub fn message_for_benchmark() -> [F; MESSAGE_LEN_FE] {
     std::array::from_fn(F::from_usize)
@@ -30,19 +29,33 @@ struct SignersCacheFile {
     signatures: Vec<(XmssPublicKey, XmssSignature)>,
 }
 
-fn cache_footprint(first_pubkey: &XmssPublicKey) -> u64 {
-    let mut hasher = DefaultHasher::new();
-    NUM_BENCHMARK_SIGNERS.hash(&mut hasher);
-    BENCHMARK_SLOT.hash(&mut hasher);
-    message_for_benchmark().hash(&mut hasher);
-    first_pubkey.merkle_root.hash(&mut hasher);
-    hasher.finish()
+fn cache_footprint(first_pubkey: &XmssPublicKey) -> u128 {
+    let mut hasher = Sha3_256::new();
+    hasher.update(NUM_BENCHMARK_SIGNERS.to_le_bytes());
+    hasher.update(BENCHMARK_SLOT.to_le_bytes());
+    for f in message_for_benchmark() {
+        hasher.update(f.as_canonical_u32().to_le_bytes());
+    }
+    for f in first_pubkey.merkle_root {
+        hasher.update(f.as_canonical_u32().to_le_bytes());
+    }
+    let hash = hasher.finalize();
+    u128::from_le_bytes(hash[..16].try_into().unwrap())
+}
+
+fn cache_dir() -> PathBuf {
+    // In CI, set SIGNERS_CACHE_DIR to a path outside target/
+    if let Ok(dir) = std::env::var("SIGNERS_CACHE_DIR") {
+        PathBuf::from(dir)
+    } else {
+        PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("../../target/signers-cache")
+    }
 }
 
 fn cache_path(first_pubkey: &XmssPublicKey) -> PathBuf {
     let footprint = cache_footprint(first_pubkey);
-    let file = format!("benchmark_signers_cache_{footprint:016x}.bin");
-    PathBuf::from(env!("CARGO_MANIFEST_DIR")).join(format!("../../target/signers-cache/{file}"))
+    let file = format!("benchmark_signers_cache_{footprint:032x}.bin");
+    cache_dir().join(file)
 }
 
 fn compute_signer(index: usize) -> (XmssPublicKey, XmssSignature) {