Move prepared key types into `sapling::keys`

We re-export them under `sapling::note_encryption` for now to make the
API changes smaller.

zcash_primitives/CHANGELOG.md

@@ -10,6 +10,8 @@ and this library adheres to Rust's notion of
 - `zcash_primitives::sapling`:
   - `keys::DiversifiedTransmissionKey`
   - `keys::{EphemeralSecretKey, EphemeralPublicKey, SharedSecret}`
+  - `keys::{PreparedIncomingViewingKey, PreparedEphemeralPublicKey}`
+    (re-exported from `note_encryption`).
   - `note`, a module containing types related to Sapling notes. The existing
     `Note` and `Rseed` types are re-exported here, and new types are added.
   - `Node::from_cmu`

zcash_primitives/src/sapling/keys.rs

@@ -8,12 +8,11 @@ use std::io::{self, Read, Write};
 
 use super::{
     address::PaymentAddress,
-    note_encryption::{
-        PreparedEphemeralPublicKey, PreparedIncomingViewingKey, KDF_SAPLING_PERSONALIZATION,
-    },
+    note_encryption::KDF_SAPLING_PERSONALIZATION,
     spec::{
         crh_ivk, diversify_hash, ka_sapling_agree, ka_sapling_agree_prepared,
-        ka_sapling_derive_public, ka_sapling_derive_public_subgroup_prepared, PreparedBaseSubgroup,
+        ka_sapling_derive_public, ka_sapling_derive_public_subgroup_prepared, PreparedBase,
+        PreparedBaseSubgroup, PreparedScalar,
     },
 };
 use crate::{
@@ -251,6 +250,27 @@ impl SaplingIvk {
     }
 }
 
+/// A Sapling incoming viewing key that has been precomputed for trial decryption.
+#[derive(Clone, Debug)]
+pub struct PreparedIncomingViewingKey(PreparedScalar);
+
+impl memuse::DynamicUsage for PreparedIncomingViewingKey {
+    fn dynamic_usage(&self) -> usize {
+        self.0.dynamic_usage()
+    }
+
+    fn dynamic_usage_bounds(&self) -> (usize, Option<usize>) {
+        self.0.dynamic_usage_bounds()
+    }
+}
+
+impl PreparedIncomingViewingKey {
+    /// Performs the necessary precomputations to use a `SaplingIvk` for note decryption.
+    pub fn new(ivk: &SaplingIvk) -> Self {
+        Self(PreparedScalar::new(&ivk.0))
+    }
+}
+
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub struct Diversifier(pub [u8; 11]);
 
@@ -280,7 +300,7 @@ impl DiversifiedTransmissionKey {
     pub(crate) fn derive(ivk: &PreparedIncomingViewingKey, d: &Diversifier) -> Option<Self> {
         d.g_d()
             .map(PreparedBaseSubgroup::new)
-            .map(|g_d| ka_sapling_derive_public_subgroup_prepared(ivk.inner(), &g_d))
+            .map(|g_d| ka_sapling_derive_public_subgroup_prepared(&ivk.0, &g_d))
             .map(DiversifiedTransmissionKey)
     }
 
@@ -382,9 +402,17 @@ impl EphemeralPublicKey {
     }
 }
 
+/// A Sapling ephemeral public key that has been precomputed for trial decryption.
+#[derive(Clone, Debug)]
+pub struct PreparedEphemeralPublicKey(PreparedBase);
+
 impl PreparedEphemeralPublicKey {
+    pub(crate) fn new(epk: jubjub::ExtendedPoint) -> Self {
+        PreparedEphemeralPublicKey(PreparedBase::new(epk))
+    }
+
     pub(crate) fn agree(&self, ivk: &PreparedIncomingViewingKey) -> SharedSecret {
-        SharedSecret(ka_sapling_agree_prepared(ivk.inner(), self.inner()))
+        SharedSecret(ka_sapling_agree_prepared(&ivk.0, &self.0))
     }
 }
 

zcash_primitives/src/sapling/note_encryption.rs

@@ -23,9 +23,8 @@ use crate::{
             DiversifiedTransmissionKey, EphemeralPublicKey, EphemeralSecretKey, OutgoingViewingKey,
             SharedSecret,
         },
-        spec::{PreparedBase, PreparedScalar},
         value::ValueCommitment,
-        Diversifier, Note, PaymentAddress, Rseed, SaplingIvk,
+        Diversifier, Note, PaymentAddress, Rseed,
     },
     transaction::components::{
         amount::Amount,
@@ -35,46 +34,11 @@ use crate::{
 
 use super::note::ExtractedNoteCommitment;
 
+pub use crate::sapling::keys::{PreparedEphemeralPublicKey, PreparedIncomingViewingKey};
+
 pub const KDF_SAPLING_PERSONALIZATION: &[u8; 16] = b"Zcash_SaplingKDF";
 pub const PRF_OCK_PERSONALIZATION: &[u8; 16] = b"Zcash_Derive_ock";
 
-/// A Sapling incoming viewing key that has been precomputed for trial decryption.
-#[derive(Clone, Debug)]
-pub struct PreparedIncomingViewingKey(PreparedScalar);
-
-impl DynamicUsage for PreparedIncomingViewingKey {
-    fn dynamic_usage(&self) -> usize {
-        self.0.dynamic_usage()
-    }
-
-    fn dynamic_usage_bounds(&self) -> (usize, Option<usize>) {
-        self.0.dynamic_usage_bounds()
-    }
-}
-
-impl PreparedIncomingViewingKey {
-    /// Performs the necessary precomputations to use a `SaplingIvk` for note decryption.
-    pub fn new(ivk: &SaplingIvk) -> Self {
-        Self(PreparedScalar::new(&ivk.0))
-    }
-
-    /// TODO: Remove after type changes.
-    pub(crate) fn inner(&self) -> &PreparedScalar {
-        &self.0
-    }
-}
-
-/// A Sapling ephemeral public key that has been precomputed for trial decryption.
-#[derive(Clone, Debug)]
-pub struct PreparedEphemeralPublicKey(PreparedBase);
-
-impl PreparedEphemeralPublicKey {
-    /// TODO: Remove after type changes.
-    pub(crate) fn inner(&self) -> &PreparedBase {
-        &self.0
-    }
-}
-
 /// Sapling PRF^ock.
 ///
 /// Implemented per section 5.4.2 of the Zcash Protocol Specification.
@@ -188,7 +152,7 @@ impl<P: consensus::Parameters> Domain for SaplingDomain<P> {
     }
 
     fn prepare_epk(epk: Self::EphemeralPublicKey) -> Self::PreparedEphemeralPublicKey {
-        PreparedEphemeralPublicKey(PreparedBase::new(epk))
+        PreparedEphemeralPublicKey::new(epk)
     }
 
     fn ka_derive_public(