Add a reference note for each first issuance

src/constants.rs

@@ -1,5 +1,6 @@
 //! Constants used in the Orchard protocol.
 pub mod fixed_bases;
+pub mod reference_keys;
 pub mod sinsemilla;
 pub mod util;
 

src/constants/reference_keys.rs

@@ -0,0 +1,54 @@
+//! Orchard reference keys, including the spending key and recipient address, used for reference notes.
+//!
+//! The reference SpendingKey is a placeholder key with all bytes set to zero.
+//! Using this SpendingKey, we derive the FullViewingKey, and the recipient address.
+//! To avoid repeating the derivation process whenever the recipient address is required, we store
+//! its raw encoding.
+
+use crate::{
+    address::Address,
+    keys::{FullViewingKey, SpendingKey},
+};
+
+/// Raw bytes representation of the reference recipient address.
+pub const RAW_REFERENCE_RECIPIENT: [u8; 43] = [
+    204, 54, 96, 25, 89, 33, 59, 107, 12, 219, 150, 167, 92, 23, 195, 166, 104, 169, 127, 13, 106,
+    140, 92, 225, 100, 165, 24, 234, 155, 169, 165, 14, 167, 81, 145, 253, 134, 27, 15, 241, 14,
+    98, 176,
+];
+
+/// Reference keys (spending key and recipient address) are used for reference notes.
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub struct ReferenceKeys;
+
+impl ReferenceKeys {
+    /// Returns the spending key for reference notes.
+    pub fn sk() -> SpendingKey {
+        SpendingKey::from_bytes([0; 32]).unwrap()
+    }
+
+    /// Returns the recipient address for reference notes.
+    pub fn recipient() -> Address {
+        Address::from_raw_address_bytes(&RAW_REFERENCE_RECIPIENT).unwrap()
+    }
+
+    /// Returns the full viewing key for reference notes.
+    pub fn fvk() -> FullViewingKey {
+        FullViewingKey::from(&Self::sk())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::keys::{FullViewingKey, Scope};
+
+    #[test]
+    fn recipient() {
+        let sk = SpendingKey::from_bytes([0; 32]).unwrap();
+        let fvk = FullViewingKey::from(&sk);
+        let recipient = fvk.address_at(0u32, Scope::External);
+
+        assert_eq!(recipient, ReferenceKeys::recipient());
+    }
+}