feat: improve poseidon API (#109)

Co-authored-by: Charpa <[email protected]>

Author: varun-doshi

crates/starknet-types-core/src/hash/pedersen.rs

@@ -17,6 +17,9 @@ impl StarkHash for Pedersen {
 
     /// Computes the Pedersen hash of an array of Felts, as defined
     /// in <https://docs.starknet.io/documentation/architecture_and_concepts/Hashing/hash-functions/#array_hashing.>
+    ///
+    /// Warning: there is room for collision as:
+    /// Pedersen::hash_array([value]) and Pedersen::hash(Pedersen::hash(0, value), 1) will return the same values
     fn hash_array(felts: &[Felt]) -> Felt {
         let data_len = Felt::from(felts.len());
         let current_hash: FieldElement<Stark252PrimeField> = felts
@@ -26,12 +29,43 @@ impl StarkHash for Pedersen {
             });
         Felt(PedersenStarkCurve::hash(&current_hash, &data_len.0))
     }
+
+    /// Computes the Pedersen hash of a single Felt
+    ///
+    /// Warning: there is room for collision as:
+    /// Pedersen::hash_single(value) and Pedersen::hash(value, 0) will return the same values
+    fn hash_single(felt: &Felt) -> Felt {
+        Felt(PedersenStarkCurve::hash(&felt.0, &Felt::from(0).0))
+    }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
+    #[test]
+    fn test_pedersen_hash_single() {
+        let x =
+            Felt::from_hex("0x03d937c035c878245caf64531a5756109c53068da139362728feb561405371cb")
+                .unwrap();
+        assert_eq!(
+            Pedersen::hash_single(&x),
+            Felt::from_hex("0x460ded9dacd215bcfc43f1b30b2a02690378e00f82a2283617d47d948c7b7f1")
+                .unwrap()
+        )
+    }
+
+    #[test]
+    fn test_pedersen_hash_collision() {
+        let x =
+            Felt::from_hex("0x03d937c035c878245caf64531a5756109c53068da139362728feb561405371cb")
+                .unwrap();
+        assert_eq!(
+            Pedersen::hash_single(&x),
+            Pedersen::hash(&x, &Felt::from(0))
+        )
+    }
+
     #[test]
     fn test_pedersen_hash() {
         let x =

crates/starknet-types-core/src/hash/poseidon.rs

@@ -28,6 +28,10 @@ impl StarkHash for Poseidon {
             )
         }))
     }
+
+    fn hash_single(felt: &Felt) -> Felt {
+        Felt(PoseidonCairoStark252::hash_single(&felt.0))
+    }
 }
 
 impl Poseidon {
@@ -46,6 +50,17 @@ impl Poseidon {
 mod tests {
     use super::*;
 
+    #[test]
+    fn test_poseidon_single() {
+        let x = Felt::from_hex("0x9").unwrap();
+
+        assert_eq!(
+            Poseidon::hash_single(&x),
+            Felt::from_hex("0x3bb3b91c714cb47003947f36dadc98326176963c434cd0a10320b8146c948b3")
+                .unwrap()
+        );
+    }
+
     #[test]
     fn test_poseidon_hash() {
         let x =

crates/starknet-types-core/src/hash/traits.rs

@@ -7,4 +7,6 @@ pub trait StarkHash {
     /// Computes the hash of an array of Felts,
     /// as defined in <https://docs.starknet.io/documentation/architecture_and_concepts/Hashing/hash-functions/#array_hashing.>
     fn hash_array(felts: &[Felt]) -> Felt;
+
+    fn hash_single(felt: &Felt) -> Felt;
 }