Merge pull request #1 from worldcoin/philsippl/extract_external_nullifier

extract external_nullifier calculation

README.md

@@ -32,21 +32,22 @@ let (_, leaf) = id.commitment().to_bytes_be();
 tree.set(0, leaf.into());
 
 let merkle_proof = tree.proof(0).expect("proof should exist");
-let root = tree.root().into();
+let root = tree.root();
 
 // change signal and external_nullifier here
-let signal = "hello".as_bytes();
-let external_nullifier = "123".as_bytes();
+let signal = "xxx".as_bytes();
+let external_nullifier = "appId".as_bytes();
 
-let nullifier_hash = generate_nullifier_hash(&id, external_nullifier);
+let external_nullifier_hash = hash_external_nullifier(external_nullifier);
+let nullifier_hash = generate_nullifier_hash(&id, &external_nullifier_hash);
 
 let config = SnarkFileConfig {
     zkey: "./semaphore/build/snark/semaphore_final.zkey".to_string(),
     wasm: "./semaphore/build/snark/semaphore.wasm".to_string(),
 };
 
-let proof = generate_proof(&config, &id, &merkle_proof, external_nullifier, signal).unwrap();
-let success = verify_proof(&config, &root, &nullifier_hash, signal, external_nullifier, &proof).unwrap();
+let proof = generate_proof(&config, &id, &merkle_proof, &external_nullifier_hash, signal).unwrap();
+let success = verify_proof(&config, &root.into(), &nullifier_hash, signal, &external_nullifier_hash, &proof).unwrap();
 
 assert!(success);
 ```

src/lib.rs

@@ -43,7 +43,8 @@ mod test {
         let signal = "xxx".as_bytes();
         let external_nullifier = "appId".as_bytes();
 
-        let nullifier_hash = generate_nullifier_hash(&id, external_nullifier);
+        let external_nullifier_hash = hash_external_nullifier(external_nullifier);
+        let nullifier_hash = generate_nullifier_hash(&id, &external_nullifier_hash);
 
         let config = SnarkFileConfig {
             zkey: "./semaphore/build/snark/semaphore_final.zkey".to_string(),
@@ -51,14 +52,14 @@ mod test {
         };
 
         let proof =
-            generate_proof(&config, &id, &merkle_proof, external_nullifier, signal).unwrap();
+            generate_proof(&config, &id, &merkle_proof, &external_nullifier_hash, signal).unwrap();
 
         let success = verify_proof(
             &config,
             &root.into(),
             &nullifier_hash,
             signal,
-            external_nullifier,
+            &external_nullifier_hash,
             &proof,
         )
         .unwrap();

src/protocol.rs

@@ -45,17 +45,23 @@ fn hash_signal(signal: &[u8]) -> BigInt {
 }
 
 /// Internal helper to hash the external nullifier
-pub fn hash_external_nullifier(nullifier: &[u8]) -> BigInt {
-    let mut hash = keccak256(nullifier).to_vec();
-    hash.splice(..3, vec![0; 4]);
-    BigInt::from_bytes_be(Sign::Plus, &hash)
+pub fn hash_external_nullifier(nullifier: &[u8]) -> [u8; 32] {
+    let mut hash = keccak256(nullifier);
+    hash[0] = 0;
+    hash[1] = 0;
+    hash[2] = 0;
+    hash[3] = 0;
+    hash
 }
 
 /// Generates the nullifier hash
 pub fn generate_nullifier_hash(identity: &Identity, external_nullifier: &[u8]) -> BigInt {
     let res = POSEIDON
         .hash(vec![
-            bigint_to_fr(&hash_external_nullifier(external_nullifier)),
+            bigint_to_fr(&BigInt::from_bytes_be(
+                Sign::Plus,
+                external_nullifier,
+            )),
             bigint_to_fr(&identity.nullifier),
         ])
         .unwrap();
@@ -90,7 +96,7 @@ pub fn generate_proof(
             merkle_proof_to_vec(merkle_proof),
         );
         inputs.insert("externalNullifier".to_string(), vec![
-            hash_external_nullifier(external_nullifier),
+            BigInt::from_bytes_be(Sign::Plus, external_nullifier),
         ]);
         inputs.insert("signalHash".to_string(), vec![hash_signal(signal)]);
 
@@ -151,7 +157,7 @@ pub fn verify_proof(
         Fp256::from(nullifier_hash.to_biguint().unwrap()),
         Fp256::from(hash_signal(signal).to_biguint().unwrap()),
         Fp256::from(
-            hash_external_nullifier(external_nullifier)
+            BigInt::from_bytes_be(Sign::Plus, external_nullifier)
                 .to_biguint()
                 .unwrap(),
         ),