docs: hashablekey trait (#1653)

crates/prover/src/types.rs

@@ -44,18 +44,33 @@ pub trait HashableKey {
     /// Hash the key into a digest of BabyBear elements.
     fn hash_babybear(&self) -> [BabyBear; DIGEST_SIZE];
 
-    /// Hash the key into a digest of  u32 elements.
+    /// Hash the key into a digest of u32 elements.
     fn hash_u32(&self) -> [u32; DIGEST_SIZE];
 
+    /// Hash the key into a Bn254Fr element.
     fn hash_bn254(&self) -> Bn254Fr {
         babybears_to_bn254(&self.hash_babybear())
     }
 
+    /// Hash the key into a 32 byte hex string, prefixed with "0x".
+    ///
+    /// This is ideal for generating a vkey hash for onchain verification.
     fn bytes32(&self) -> String {
         let vkey_digest_bn254 = self.hash_bn254();
         format!("0x{:0>64}", vkey_digest_bn254.as_canonical_biguint().to_str_radix(16))
     }
 
+    /// Hash the key into a 32 byte array.
+    ///
+    /// This has the same value as `bytes32`, but as a raw byte array.
+    fn bytes32_raw(&self) -> [u8; 32] {
+        let vkey_digest_bn254 = self.hash_bn254();
+        let vkey_bytes = vkey_digest_bn254.as_canonical_biguint().to_bytes_be();
+        let mut result = [0u8; 32];
+        result[1..].copy_from_slice(&vkey_bytes);
+        result
+    }
+
     /// Hash the key into a digest of bytes elements.
     fn hash_bytes(&self) -> [u8; DIGEST_SIZE * 4] {
         words_to_bytes_be(&self.hash_u32())