added basic code for schnorr signatures

src/crypto/mod.rs

@@ -1,6 +1,8 @@
 pub mod diffie_hellman;
 pub mod mint_proof;
+pub mod schnorr;
 pub mod spend_proof;
+pub mod util;
 
 use bellman::groth16;
 use bls12_381::Bls12;

src/crypto/schnorr.rs

@@ -0,0 +1,25 @@
+use ff::Field;
+use group::{Group, GroupEncoding};
+use rand::rngs::OsRng;
+
+use super::util::hash_to_scalar;
+
+#[test]
+fn test_schnorr() {
+    let secret = jubjub::Fr::random(&mut OsRng);
+    let public = zcash_primitives::constants::SPENDING_KEY_GENERATOR * secret;
+
+    let mask = jubjub::Fr::random(&mut OsRng);
+    let commit = zcash_primitives::constants::SPENDING_KEY_GENERATOR * mask;
+
+    let msg = b"Foo bar";
+    let challenge = hash_to_scalar(b"DarkFi_Schnorr", &commit.to_bytes(), &msg[..]);
+
+    let response = mask + challenge * secret;
+
+    // Verify signature
+
+    assert_eq!(
+        zcash_primitives::constants::SPENDING_KEY_GENERATOR * response - public * challenge, commit);
+}
+

src/crypto/util.rs

@@ -0,0 +1,10 @@
+use blake2b_simd::Params;
+
+pub fn hash_to_scalar(persona: &[u8], a: &[u8], b: &[u8]) -> jubjub::Fr {
+    let mut hasher = Params::new().hash_length(64).personal(persona).to_state();
+    hasher.update(a);
+    hasher.update(b);
+    let ret = hasher.finalize();
+    jubjub::Fr::from_bytes_wide(ret.as_array())
+}
+