Import identity.rs from semaphore-rs

rln/src/identity.rs

@@ -0,0 +1,64 @@
+use num_bigint::{BigInt, Sign};
+use once_cell::sync::Lazy;
+use poseidon_rs::Poseidon;
+use sha2::{Digest, Sha256};
+
+use crate::util::{bigint_to_fr, fr_to_bigint};
+
+// Adapted from
+// https://github.com/worldcoin/semaphore-rs/blob/main/src/identity.rs
+
+static POSEIDON: Lazy<Poseidon> = Lazy::new(Poseidon::new);
+
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct Identity {
+    pub trapdoor:  BigInt,
+    pub nullifier: BigInt,
+}
+
+// todo: improve
+fn sha(msg: &[u8]) -> [u8; 32] {
+    let mut hasher = Sha256::new();
+    hasher.update(msg);
+    let result = hasher.finalize();
+    let res: [u8; 32] = result.into();
+    res
+}
+
+impl Identity {
+    pub fn new(seed: &[u8]) -> Self {
+        let seed_hash = &sha(seed);
+
+        // https://github.com/appliedzkp/zk-kit/blob/1ea410456fc2b95877efa7c671bc390ffbfb5d36/packages/identity/src/identity.ts#L58
+        let trapdoor = BigInt::from_bytes_be(
+            Sign::Plus,
+            &sha(format!("{}identity_trapdoor", hex::encode(seed_hash)).as_bytes()),
+        );
+        let nullifier = BigInt::from_bytes_be(
+            Sign::Plus,
+            &sha(format!("{}identity_nullifier", hex::encode(seed_hash)).as_bytes()),
+        );
+
+        Self {
+            trapdoor,
+            nullifier,
+        }
+    }
+
+    pub fn secret_hash(&self) -> BigInt {
+        let res = POSEIDON
+            .hash(vec![
+                bigint_to_fr(&self.nullifier),
+                bigint_to_fr(&self.trapdoor),
+            ])
+            .unwrap();
+        fr_to_bigint(res)
+    }
+
+    pub fn commitment(&self) -> BigInt {
+        let res = POSEIDON
+            .hash(vec![bigint_to_fr(&self.secret_hash())])
+            .unwrap();
+        fr_to_bigint(res)
+    }
+}