Add the beginnings of Sprout and Sapling key types

zebra-chain/src/addresses.rs

@@ -1,3 +1,5 @@
 //! Address types.
 
+pub mod sapling;
+pub mod sprout;
 pub mod transparent;

zebra-chain/src/keys/sapling.rs

@@ -1,4 +1,11 @@
 //! Sapling key types
+//!
+//! "The spend authorizing key ask, proof authorizing key (ak, nsk),
+//! full viewing key (ak, nk, ovk), incoming viewing key ivk, and each
+//! diversied payment address addr_d = (d, pk_d ) are derived from sk,
+//! as described in [Sapling Key Components][ps]."
+//!
+//! [ps]: https://zips.z.cash/protocol/protocol.pdf#saplingkeycomponents
 
 use std::{
     fmt,

zebra-chain/src/keys/sprout.rs

@@ -1,4 +1,10 @@
 //! Sprout key types
+//!
+//! "The receiving key sk_enc, the incoming viewing key ivk = (apk,
+//! sk_enc), and the shielded payment address addr_pk = (a_pk, pk_enc) are
+//! derived from a_sk, as described in [‘Sprout Key Components’][ps]
+//!
+//! [ps]: https://zips.z.cash/protocol/protocol.pdf#sproutkeycomponents
 
 use std::{
     fmt,
@@ -12,6 +18,20 @@ use proptest_derive::Arbitrary;
 
 use crate::serialization::{SerializationError, ZcashDeserialize, ZcashSerialize};
 
+/// All other Sprout key types derive from the SpendingKey value.
+pub struct SpendingKey;
+
+pub struct ReceivingKey;
+
+pub struct PayingKey;
+
+pub struct TransmissionKey;
+
+pub struct IncomingViewingKey {
+    paying_key: PayingKey,
+    receiving_key: ReceivingKey,
+}
+
 #[cfg(test)]
 proptest! {