Implementation of Sapling key agreement.

src/tests/key_agreement.rs

@@ -0,0 +1,74 @@
+use pairing::bls12_381::Bls12;
+use pairing::{PrimeField, PrimeFieldRepr};
+use rand::{OsRng, Rng};
+use sapling_crypto::jubjub::{edwards, JubjubBls12};
+use sapling_crypto::primitives::{Diversifier, ViewingKey};
+
+use {
+    librustzcash_sapling_generate_r, librustzcash_sapling_ka_agree,
+    librustzcash_sapling_ka_derivepublic,
+};
+
+#[test]
+fn test_key_agreement() {
+    let params = JubjubBls12::new();
+    let mut rng = OsRng::new().unwrap();
+
+    // Create random viewing key
+    let vk = ViewingKey::<Bls12> {
+        ak: edwards::Point::rand(&mut rng, &params).mul_by_cofactor(&params),
+        nk: edwards::Point::rand(&mut rng, &params).mul_by_cofactor(&params),
+    };
+
+    // Create a random address with the viewing key
+    let addr = loop {
+        match vk.into_payment_address(Diversifier(rng.gen()), &params) {
+            Some(a) => break a,
+            None => {}
+        }
+    };
+
+    // Grab ivk from our viewing key in serialized form
+    let ivk = vk.ivk();
+    let mut ivk_serialized = [0u8; 32];
+    ivk.into_repr().write_le(&mut ivk_serialized[..]).unwrap();
+
+    // Create random esk
+    let mut esk = [0u8; 32];
+    librustzcash_sapling_generate_r(&mut esk);
+
+    // The sender will create a shared secret with the recipient
+    // by multiplying the pk_d from their address with the esk
+    // we randomly generated
+    let mut shared_secret_sender = [0u8; 32];
+
+    // Serialize pk_d for the call to librustzcash_sapling_ka_agree
+    let mut addr_pk_d = [0u8; 32];
+    addr.pk_d.write(&mut addr_pk_d[..]).unwrap();
+
+    assert!(librustzcash_sapling_ka_agree(
+        &addr_pk_d,
+        &esk,
+        &mut shared_secret_sender
+    ));
+
+    // Create epk for the recipient, placed in the transaction. Computed
+    // using the diversifier and esk.
+    let mut epk = [0u8; 32];
+    assert!(librustzcash_sapling_ka_derivepublic(
+        &addr.diversifier.0,
+        &esk,
+        &mut epk
+    ));
+
+    // Create sharedSecret with ephemeral key
+    let mut shared_secret_recipient = [0u8; 32];
+    assert!(librustzcash_sapling_ka_agree(
+        &epk,
+        &ivk_serialized,
+        &mut shared_secret_recipient
+    ));
+
+    assert!(!shared_secret_sender.iter().all(|&v| v == 0));
+    assert_eq!(shared_secret_sender, shared_secret_recipient);
+}

src/tests/mod.rs

@@ -5,6 +5,7 @@ use super::JUBJUB;
 mod notes;
 mod key_components;
 mod signatures;
+mod key_agreement;
 
 #[test]
 fn sapling_generators() {