feat: add hash_public_values

core/Cargo.toml

@@ -59,6 +59,7 @@ web-time = "1.1.0"
 rayon-scan = "0.1.1"
 serial_test = "3.1.1"
 thiserror = "1.0.60"
+num-bigint = { version = "0.4.3", default-features = false }
 
 [dev-dependencies]
 tiny-keccak = { version = "2.0.2", features = ["keccak"] }

core/src/io.rs

@@ -2,6 +2,8 @@ use crate::{
     stark::{ShardProof, StarkVerifyingKey},
     utils::{BabyBearPoseidon2, Buffer},
 };
+use k256::sha2::{Digest, Sha256};
+use num_bigint::BigUint;
 use serde::{de::DeserializeOwned, Deserialize, Serialize};
 
 /// Standard input for the prover.
@@ -127,6 +129,26 @@ impl SP1PublicValues {
     pub fn write_slice(&mut self, slice: &[u8]) {
         self.buffer.write_slice(slice);
     }
+
+    /// Hash the public values, mask the top 3 bits and return a BigUint.
+    /// Matches the implementation of hashPublicValues in the Solidity verifier.
+    ///
+    /// ```
+    /// return sha256(publicValues) & bytes32(uint256((1 << 253) - 1));
+    /// ```
+    pub fn hash_public_values(&self) -> BigUint {
+        // Hash the public values.
+        let mut hasher = Sha256::new();
+        hasher.update(self.buffer.data.as_slice());
+        let hash_result = hasher.finalize();
+        let mut hash = hash_result.to_vec();
+
+        // Mask the top 3 bits.
+        hash[0] &= 0b00011111;
+
+        // Return the masked hash as a BigUint.
+        BigUint::from_bytes_be(&hash)
+    }
 }
 
 impl AsRef<[u8]> for SP1PublicValues {
@@ -172,3 +194,23 @@ pub mod proof_serde {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_hash_public_values() {
+        let random_hex = "1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef";
+        let random_bytes = hex::decode(random_hex).unwrap();
+
+        let expected_hash = "1ce987d0a7fcc2636fe87e69295ba12b1cc46c256b369ae7401c51b805ee91bd";
+        let expected_hash_biguint = BigUint::from_bytes_be(&hex::decode(expected_hash).unwrap());
+
+        let mut public_values = SP1PublicValues::new();
+        public_values.write_slice(&random_bytes);
+        let hash = public_values.hash_public_values();
+
+        assert_eq!(hash, expected_hash_biguint);
+    }
+}