[#1924] Add zcash_voting dependency foundation

CHANGELOG.md

@@ -6,6 +6,9 @@ and this library adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- Added the Rust `zcash_voting` dependency foundation for future shielded voting backend work.
+
 ### Changed
 - `Synchronizer.importAccountByUfvk` now calls `TypesafeBackend.rewindToChainState` after importing
   an account. This enables imported accounts to discover their history and funds, at the cost of

backend-lib/Cargo.toml

@@ -12,7 +12,7 @@ rust-version = "1.92"
 
 [dependencies]
 # Zcash dependencies
-orchard = "0.13"
+orchard = { version = "=0.13.1", features = ["unstable-voting-circuits"] }
 pczt = { version = "0.6", features = ["prover", "orchard", "sapling"] }
 sapling = { package = "sapling-crypto", version = "0.7", default-features = false }
 transparent = { package = "zcash_transparent", version = "0.7", default-features = false }
@@ -77,6 +77,9 @@ xz2 = { version = "0.1", features = ["static"] }
 component = "0.1.1"
 rust-analyzer = "0.0.1"
 
+# Shielded voting
+zcash_voting = { version = "0.5.3", default-features = false }
+
 ## Uncomment this to test librustzcash changes locally
 #[patch.crates-io]
 #pczt = { package = "pczt", path = '../../clones/librustzcash/pczt' }

backend-lib/src/main/java/cash/z/ecc/android/sdk/internal/jni/VotingRustBackend.kt

@@ -0,0 +1,15 @@
+package cash.z.ecc.android.sdk.internal.jni
+
+internal object VotingRustBackend {
+    suspend fun new(): VotingRustBackend {
+        RustBackend.loadLibrary()
+        return this
+    }
+
+    @JvmStatic
+    external fun computeShareNullifier(
+        voteCommitment: ByteArray,
+        primaryBlind: ByteArray,
+        shareIndex: Int
+    ): ByteArray?
+}

backend-lib/src/main/rust/lib.rs

@@ -103,6 +103,7 @@ use crate::utils::{
 mod eip681;
 mod tor;
 mod utils;
+mod voting;
 
 #[cfg(debug_assertions)]
 fn print_debug_state() {

backend-lib/src/main/rust/voting.rs

@@ -0,0 +1,45 @@
+//! JNI bindings for the zcash_voting crate.
+
+use std::ptr;
+
+use anyhow::anyhow;
+use jni::{
+    JNIEnv,
+    objects::{JByteArray, JClass},
+    sys::{jbyteArray, jint},
+};
+use zcash_voting as voting;
+
+use crate::utils::{self, catch_unwind, exception::unwrap_exc_or};
+
+/// Compute the share reveal nullifier from client-known inputs.
+///
+/// Returns the 32-byte nullifier, or throws a RuntimeException and returns null
+/// on malformed inputs.
+#[unsafe(no_mangle)]
+pub extern "C" fn Java_cash_z_ecc_android_sdk_internal_jni_VotingRustBackend_computeShareNullifier<
+    'local,
+>(
+    mut env: JNIEnv<'local>,
+    _: JClass<'local>,
+    vote_commitment: JByteArray<'local>,
+    primary_blind: JByteArray<'local>,
+    share_index: jint,
+) -> jbyteArray {
+    let res = catch_unwind(&mut env, |env| {
+        let share_index =
+            u32::try_from(share_index).map_err(|_| anyhow!("shareIndex must be non-negative"))?;
+        let vote_commitment = utils::java_bytes_to_rust(env, &vote_commitment)?;
+        let primary_blind = utils::java_bytes_to_rust(env, &primary_blind)?;
+
+        let nullifier = voting::share_tracking::compute_share_nullifier(
+            &vote_commitment,
+            share_index,
+            &primary_blind,
+        )
+        .map_err(|e| anyhow!("compute_share_nullifier failed: {}", e))?;
+
+        Ok(utils::rust_bytes_to_java(env, &nullifier)?.into_raw())
+    });
+    unwrap_exc_or(&mut env, res, ptr::null_mut())
+}