From a28947d142b48a3f5a54395428c5690f954594d3 Mon Sep 17 00:00:00 2001
From: Sebastian Messmer <messmer@cryfs.org>
Date: Wed, 22 Oct 2025 22:11:41 -0700
Subject: [PATCH] Parallelize scrypt with rayon

---
 Cargo.lock            |  1 +
 scrypt/Cargo.toml     |  4 +++-
 scrypt/benches/lib.rs | 14 +++++++++++++-
 scrypt/src/lib.rs     | 27 +++++++++++++++++++++++----
 4 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 7102251a..544f2a2f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -419,6 +419,7 @@ version = "0.12.0-rc.2"
 dependencies = [
  "password-hash",
  "pbkdf2",
+ "rayon",
  "salsa20",
  "sha2",
 ]
diff --git a/scrypt/Cargo.toml b/scrypt/Cargo.toml
index 7622727c..295fe4d9 100644
--- a/scrypt/Cargo.toml
+++ b/scrypt/Cargo.toml
@@ -17,6 +17,7 @@ rust-version = "1.85"
 pbkdf2 = { version = "0.13.0-rc.1", path = "../pbkdf2" }
 salsa20 = { version = "0.11.0-rc.1", default-features = false }
 sha2 = { version = "0.11.0-rc.2", default-features = false }
+rayon = { version = "1.11", optional = true }
 
 # optional dependencies
 password-hash = { version = "0.6.0-rc.1", default-features = false, features = ["rand_core"], optional = true }
@@ -25,8 +26,9 @@ password-hash = { version = "0.6.0-rc.1", default-features = false, features = [
 password-hash = { version = "0.6.0-rc.1", features = ["rand_core"] }
 
 [features]
-default = ["simple"]
+default = ["simple", "rayon"]
 simple = ["password-hash"]
+rayon = ["dep:rayon"]
 
 [package.metadata.docs.rs]
 all-features = true
diff --git a/scrypt/benches/lib.rs b/scrypt/benches/lib.rs
index 4e400153..423c6248 100644
--- a/scrypt/benches/lib.rs
+++ b/scrypt/benches/lib.rs
@@ -6,7 +6,7 @@ extern crate test;
 use test::Bencher;
 
 #[bench]
-pub fn scrypt_15_8_1(bh: &mut Bencher) {
+pub fn scrypt_17_8_1(bh: &mut Bencher) {
     let password = b"my secure password";
     let salt = b"salty salt";
     let mut buf = [0u8; 32];
@@ -16,3 +16,15 @@ pub fn scrypt_15_8_1(bh: &mut Bencher) {
         test::black_box(&buf);
     });
 }
+
+#[bench]
+pub fn scrypt_17_2_4(bh: &mut Bencher) {
+    let password = b"my secure password";
+    let salt = b"salty salt";
+    let mut buf = [0u8; 32];
+    let params = scrypt::Params::new(17, 2, 4).unwrap();
+    bh.iter(|| {
+        scrypt::scrypt(password, salt, &params, &mut buf).unwrap();
+        test::black_box(&buf);
+    });
+}
diff --git a/scrypt/src/lib.rs b/scrypt/src/lib.rs
index 03bca3fa..57976860 100644
--- a/scrypt/src/lib.rs
+++ b/scrypt/src/lib.rs
@@ -112,13 +112,32 @@ pub fn scrypt(
     let mut b = vec![0u8; pr128];
     pbkdf2_hmac::<Sha256>(password, salt, 1, &mut b);
 
+    #[cfg(not(feature = "rayon"))]
+    romix_sequential(nr128, r128, n, &mut b);
+    #[cfg(feature = "rayon")]
+    romix_parallel(nr128, r128, n, &mut b);
+
+    pbkdf2_hmac::<Sha256>(password, &b, 1, output);
+    Ok(())
+}
+
+#[cfg(not(feature = "rayon"))]
+fn romix_sequential(nr128: usize, r128: usize, n: usize, b: &mut [u8]) {
     let mut v = vec![0u8; nr128];
     let mut t = vec![0u8; r128];
 
-    for chunk in &mut b.chunks_mut(r128) {
+    b.chunks_mut(r128).for_each(|chunk| {
         romix::scrypt_ro_mix(chunk, &mut v, &mut t, n);
-    }
+    });
+}
 
-    pbkdf2_hmac::<Sha256>(password, &b, 1, output);
-    Ok(())
+#[cfg(feature = "rayon")]
+fn romix_parallel(nr128: usize, r128: usize, n: usize, b: &mut [u8]) {
+    use rayon::{iter::ParallelIterator as _, slice::ParallelSliceMut as _};
+
+    b.par_chunks_mut(r128).for_each(|chunk| {
+        let mut v = vec![0u8; nr128];
+        let mut t = vec![0u8; r128];
+        romix::scrypt_ro_mix(chunk, &mut v, &mut t, n);
+    });
 }