zcash_proofs: Introduce newtype wrappers for Sapling parameters

zcash_proofs/CHANGELOG.md

@@ -6,7 +6,16 @@ and this library adheres to Rust's notion of
 [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Added
+- `zcash_proofs::{SpendParameters, OutputParameters}`
+
 ### Changed
+- The new `SpendParameters` and `OutputParameters` types are used in the
+  following places:
+  - `zcash_proofs::ZcashParameters::{spend_params, output_params}` fields.
+  - `zcash_proofs::sapling::prover`:
+    - `SaplingProvingContext::{spend_proof, output_proof}` (the `proving_key`
+      arguments).
 - `zcash_proofs::sapling::prover`:
   - The `verifying_key` argument `SaplingProvingContext::spend_proof` has been
     removed. Callers should instead use `SaplingVerifyingContext` to verify

zcash_proofs/src/lib.rs

@@ -283,11 +283,17 @@ fn stream_params_downloads_to_disk(
     Ok(())
 }
 
+/// The parameters for the Sapling Spend circuit.
+pub struct SpendParameters(Parameters<Bls12>);
+
+/// The parameters for the Sapling Output circuit.
+pub struct OutputParameters(Parameters<Bls12>);
+
 /// Zcash Sprout and Sapling groth16 circuit parameters.
 pub struct ZcashParameters {
-    pub spend_params: Parameters<Bls12>,
+    pub spend_params: SpendParameters,
     pub spend_vk: PreparedVerifyingKey<Bls12>,
-    pub output_params: Parameters<Bls12>,
+    pub output_params: OutputParameters,
     pub output_vk: PreparedVerifyingKey<Bls12>,
     pub sprout_vk: Option<PreparedVerifyingKey<Bls12>>,
 }
@@ -429,9 +435,9 @@ pub fn parse_parameters<R: io::Read>(
     let sprout_vk = sprout_vk.map(|vk| prepare_verifying_key(&vk));
 
     ZcashParameters {
-        spend_params,
+        spend_params: SpendParameters(spend_params),
         spend_vk,
-        output_params,
+        output_params: OutputParameters(output_params),
         output_vk,
         sprout_vk,
     }

zcash_proofs/src/prover.rs

@@ -1,6 +1,6 @@
 //! Abstractions over the proving system and parameters for ease of use.
 
-use bellman::groth16::{Parameters, PreparedVerifyingKey};
+use bellman::groth16::PreparedVerifyingKey;
 use bls12_381::Bls12;
 use std::path::Path;
 use zcash_primitives::{
@@ -13,7 +13,10 @@ use zcash_primitives::{
     transaction::components::{Amount, GROTH_PROOF_SIZE},
 };
 
-use crate::{load_parameters, parse_parameters, sapling::SaplingProvingContext};
+use crate::{
+    load_parameters, parse_parameters, sapling::SaplingProvingContext, OutputParameters,
+    SpendParameters,
+};
 
 #[cfg(feature = "local-prover")]
 use crate::{default_params_folder, SAPLING_OUTPUT_NAME, SAPLING_SPEND_NAME};
@@ -21,12 +24,12 @@ use crate::{default_params_folder, SAPLING_OUTPUT_NAME, SAPLING_SPEND_NAME};
 /// An implementation of [`TxProver`] using Sapling Spend and Output parameters from
 /// locally-accessible paths.
 pub struct LocalTxProver {
-    spend_params: Parameters<Bls12>,
+    spend_params: SpendParameters,
     // TODO: Either re-introduce verification-after-proving (once the verifier is
     // refactored), or remove this.
     #[allow(unused)]
     spend_vk: PreparedVerifyingKey<Bls12>,
-    output_params: Parameters<Bls12>,
+    output_params: OutputParameters,
 }
 
 impl LocalTxProver {

zcash_proofs/src/sapling/prover.rs

@@ -1,4 +1,4 @@
-use bellman::groth16::{create_random_proof, Parameters, Proof};
+use bellman::groth16::{create_random_proof, Proof};
 use bls12_381::Bls12;
 use group::GroupEncoding;
 use rand_core::OsRng;
@@ -13,6 +13,8 @@ use zcash_primitives::{
     transaction::components::Amount,
 };
 
+use crate::{OutputParameters, SpendParameters};
+
 /// A context object for creating the Sapling components of a Zcash transaction.
 pub struct SaplingProvingContext {
     bsk: TrapdoorSum,
@@ -48,7 +50,7 @@ impl SaplingProvingContext {
         value: u64,
         anchor: bls12_381::Scalar,
         merkle_path: MerklePath,
-        proving_key: &Parameters<Bls12>,
+        proving_key: &SpendParameters,
     ) -> Result<(Proof<Bls12>, ValueCommitment, PublicKey), ()> {
         // Initialize secure RNG
         let mut rng = OsRng;
@@ -96,8 +98,8 @@ impl SaplingProvingContext {
         };
 
         // Create proof
-        let proof =
-            create_random_proof(instance, proving_key, &mut rng).expect("proving should not fail");
+        let proof = create_random_proof(instance, &proving_key.0, &mut rng)
+            .expect("proving should not fail");
 
         // Accumulate the value commitment in the context
         self.cv_sum += &value_commitment;
@@ -114,7 +116,7 @@ impl SaplingProvingContext {
         payment_address: PaymentAddress,
         rcm: jubjub::Fr,
         value: u64,
-        proving_key: &Parameters<Bls12>,
+        proving_key: &OutputParameters,
     ) -> (Proof<Bls12>, ValueCommitment) {
         // Initialize secure RNG
         let mut rng = OsRng;
@@ -143,8 +145,8 @@ impl SaplingProvingContext {
         };
 
         // Create proof
-        let proof =
-            create_random_proof(instance, proving_key, &mut rng).expect("proving should not fail");
+        let proof = create_random_proof(instance, &proving_key.0, &mut rng)
+            .expect("proving should not fail");
 
         // Accumulate the value commitment in the context. We do this to check internal consistency.
         self.cv_sum -= &value_commitment; // Outputs subtract from the total.