add nullifier constructor

nssa/core/src/account/commitment.rs

@@ -7,7 +7,7 @@ use serde::{Deserialize, Serialize};
 use crate::account::{Account, NullifierPublicKey};
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, Hash)]
-pub struct Commitment([u8; 32]);
+pub struct Commitment(pub(super) [u8; 32]);
 
 impl Commitment {
     pub fn new(Npk: &NullifierPublicKey, account: &Account) -> Self {

nssa/core/src/account/encoding.rs

@@ -3,7 +3,7 @@ use risc0_zkvm::{
     sha::{Impl, Sha256},
 };
 
-use crate::account::Account;
+use crate::account::{Account, Commitment, NullifierPublicKey};
 
 impl Account {
     pub fn to_bytes(&self) -> Vec<u8> {
@@ -19,6 +19,19 @@ impl Account {
     }
 }
 
+impl Commitment {
+    pub(crate) fn to_bytes(&self) -> [u8; 32] {
+        self.0
+    }
+}
+
+
+impl NullifierPublicKey {
+    pub(crate) fn to_bytes(&self) -> [u8; 32] {
+        self.0
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::account::Account;

nssa/core/src/account/nullifier.rs

@@ -1,15 +1,10 @@
+use risc0_zkvm::sha::{Impl, Sha256};
 use serde::{Deserialize, Serialize};
 
 use crate::account::Commitment;
 
 #[derive(Debug, Serialize, Deserialize, PartialEq, Eq)]
-pub struct NullifierPublicKey([u8; 32]);
-
-impl NullifierPublicKey {
-    pub(crate) fn to_bytes(&self) -> [u8; 32] {
-        self.0
-    }
-}
+pub struct NullifierPublicKey(pub(super) [u8; 32]);
 
 impl From<&NullifierSecretKey> for NullifierPublicKey {
     fn from(_value: &NullifierSecretKey) -> Self {
@@ -24,6 +19,26 @@ pub struct Nullifier([u8; 32]);
 
 impl Nullifier {
     pub fn new(commitment: &Commitment, nsk: &NullifierSecretKey) -> Self {
-        todo!()
+        let mut bytes = Vec::new();
+        bytes.extend_from_slice(&commitment.to_bytes());
+        bytes.extend_from_slice(nsk);
+        Self(Impl::hash_bytes(&bytes).as_bytes().try_into().unwrap())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_constructor() {
+        let commitment = Commitment((0..32u8).collect::<Vec<_>>().try_into().unwrap());
+        let nsk = [0x42; 32];
+        let expected_nullifier = Nullifier([
+            97, 87, 111, 191, 0, 44, 125, 145, 237, 104, 31, 230, 203, 254, 68, 176, 126, 17, 240,
+            205, 249, 143, 11, 43, 15, 198, 189, 219, 191, 49, 36, 61,
+        ]);
+        let nullifier = Nullifier::new(&commitment, &nsk);
+        assert_eq!(nullifier, expected_nullifier);
     }
 }