feat: alternative (slow) pedersen hash impl optimized for size (#675)

.github/workflows/test.yaml

@@ -25,6 +25,10 @@ jobs:
           profile: minimal
           override: true
 
+      - name: Test starknet-crypto with pedersen_no_lookup
+        run: |
+          cargo test -p starknet-crypto --features pedersen_no_lookup
+
       - name: Run cargo tests
         uses: nick-fields/retry@v2
         with:
@@ -53,6 +57,10 @@ jobs:
           profile: minimal
           override: true
 
+      - name: Test starknet-crypto with pedersen_no_lookup
+        run: |
+          cargo test -p starknet-crypto --features pedersen_no_lookup
+
       - name: Run cargo tests
         uses: nick-fields/retry@v2
         with:

starknet-crypto/Cargo.toml

@@ -31,6 +31,7 @@ default = ["std", "signature-display"]
 std = ["starknet-types-core/std"]
 alloc = ["hex?/alloc", "starknet-types-core/alloc"]
 signature-display = ["dep:hex", "alloc"]
+pedersen_no_lookup = []
 
 [dev-dependencies]
 criterion = { version = "0.4.0", default-features = false }

starknet-crypto/README.md

@@ -65,6 +65,14 @@ poseidon_hash_many      time:   [41.878 µs 41.911 µs 41.945 µs]
 rfc6979_generate_k      time:   [11.564 µs 11.566 µs 11.569 µs]
 ```
 
+## Binary size optimization
+
+By default, `starknet-crypto` ships with a Pedersen hash implementation utilizing a lookup table for better performance. To optimize for binary size over performance, the crate offers a `pedersen_no_lookup` feature, which uses a vanilla unoptimized implementation instead.
+
+> [!WARNING]
+>
+> Enabling the `pedersen_no_lookup` feature significantly slows down hashing performance by approximately a factor of `10`. Make sure you understand the impact on your use case before turning it on.
+
 ## Credits
 
 Most of the code in this crate for the Pedersen hash implementation was inspired and modified from the awesome [`pathfinder` from Equilibrium](https://github.com/eqlabs/pathfinder/blob/b091cb889e624897dbb0cbec3c1df9a9e411eb1e/crates/pedersen/src/lib.rs).

starknet-crypto/src/pedersen_hash/default.rs

@@ -0,0 +1,14 @@
+use starknet_types_core::{
+    felt::Felt,
+    hash::{Pedersen, StarkHash},
+};
+
+/// Computes the Starkware version of the Pedersen hash of x and y. All inputs are little-endian.
+///
+/// ### Parameters
+///
+/// - `x`: The x coordinate.
+/// - `y`: The y coordinate.
+pub fn pedersen_hash(x: &Felt, y: &Felt) -> Felt {
+    Pedersen::hash(x, y)
+}

starknet-crypto/src/pedersen_hash.rs → starknet-crypto/src/pedersen_hash/mod.rs

@@ -1,17 +1,12 @@
-use starknet_types_core::{
-    felt::Felt,
-    hash::{Pedersen, StarkHash},
-};
+#[cfg(not(feature = "pedersen_no_lookup"))]
+mod default;
+#[cfg(not(feature = "pedersen_no_lookup"))]
+pub use default::pedersen_hash;
 
-/// Computes the Starkware version of the Pedersen hash of x and y. All inputs are little-endian.
-///
-/// ### Parameters
-///
-/// - `x`: The x coordinate.
-/// - `y`: The y coordinate.
-pub fn pedersen_hash(x: &Felt, y: &Felt) -> Felt {
-    Pedersen::hash(x, y)
-}
+#[cfg(feature = "pedersen_no_lookup")]
+mod no_lookup;
+#[cfg(feature = "pedersen_no_lookup")]
+pub use no_lookup::pedersen_hash;
 
 #[cfg(test)]
 mod tests {

starknet-crypto/src/pedersen_hash/no_lookup.rs

@@ -0,0 +1,97 @@
+// Size-optimized implementation ported from:
+//   https://github.com/andrewmilson/sandstorm/blob/9e256c4933aa2d89f794b3ed7c293b32984fe1ce/builtins/src/pedersen/mod.rs#L24-L50
+
+use starknet_curve::curve_params::SHIFT_POINT;
+use starknet_types_core::{curve::ProjectivePoint, felt::Felt};
+
+/// Computes the Starkware version of the Pedersen hash of x and y. All inputs are little-endian.
+///
+/// ### Parameters
+///
+/// - `x`: The x coordinate.
+/// - `y`: The y coordinate.
+pub fn pedersen_hash(x: &Felt, y: &Felt) -> Felt {
+    // Temporarily defining the projective points inline, as `ProjectivePoint::new()` is incorrectly
+    // not `const`.
+    // TODO: turn these into consts once upstream is fixed.
+    let p0_projective: ProjectivePoint = ProjectivePoint::new(
+        Felt::from_raw([
+            241691544791834578,
+            518715844721862878,
+            13758484295849329960,
+            3602345268353203007,
+        ]),
+        Felt::from_raw([
+            368891789801938570,
+            433857700841878496,
+            13001553326386915570,
+            13441546676070136227,
+        ]),
+        Felt::ONE,
+    );
+    let p1_projective: ProjectivePoint = ProjectivePoint::new(
+        Felt::from_raw([
+            253000153565733272,
+            10043949394709899044,
+            12382025591154462459,
+            16491878934996302286,
+        ]),
+        Felt::from_raw([
+            285630633187035523,
+            5191292837124484988,
+            2545498000137298346,
+            13950428914333633429,
+        ]),
+        Felt::ONE,
+    );
+    let p2_projective: ProjectivePoint = ProjectivePoint::new(
+        Felt::from_raw([
+            338510149841406402,
+            12916675983929588442,
+            18195981508842736832,
+            1203723169299412240,
+        ]),
+        Felt::from_raw([
+            161068411212710156,
+            11088962269971685343,
+            11743524503750604092,
+            12352616181161700245,
+        ]),
+        Felt::ONE,
+    );
+    let p3_projective: ProjectivePoint = ProjectivePoint::new(
+        Felt::from_raw([
+            425493972656615276,
+            299781701614706065,
+            10664803185694787051,
+            1145636535101238356,
+        ]),
+        Felt::from_raw([
+            345457391846365716,
+            6033691581221864148,
+            4428713245976508844,
+            8187986478389849302,
+        ]),
+        Felt::ONE,
+    );
+
+    let processed_x = process_element(x, &p0_projective, &p1_projective);
+    let processed_y = process_element(y, &p2_projective, &p3_projective);
+
+    // Unwrapping is safe as this never fails
+    (processed_x + processed_y + SHIFT_POINT)
+        .to_affine()
+        .unwrap()
+        .x()
+}
+
+#[inline(always)]
+fn process_element(x: &Felt, p1: &ProjectivePoint, p2: &ProjectivePoint) -> ProjectivePoint {
+    let x = x.to_biguint();
+    let shift = 252 - 4;
+    let high_part = &x >> shift;
+    let low_part = x - (&high_part << shift);
+    let x_high = Felt::from(high_part);
+    let x_low = Felt::from(low_part);
+    p1 * x_low + p2 * x_high
+}