Add function librustzcash_sapling_compute_nf.

Also add function priv_get_note to refactor common code from librustzcash_sapling_compute_cm.

include/librustzcash.h

@@ -102,6 +102,23 @@ extern "C" {
     /// `librustzcash_sapling_verification_ctx_init`.
     void librustzcash_sapling_verification_ctx_free(void *);
 
+    /// Compute a Sapling nullifier.
+    ///
+    /// The `diversifier` parameter must be 11 bytes in length.
+    /// The `pk_d`, `r`, `ak` and `nk` parameters must be of length 32.
+    /// The result is also of length 32 and placed in `result`.
+    /// Returns false if the diversifier or pk_d is not valid
+    bool librustzcash_sapling_compute_nf(
+        const unsigned char *diversifier,
+        const unsigned char *pk_d,
+        const uint64_t value,
+        const unsigned char *r,
+        const unsigned char *ak,
+        const unsigned char *nk,
+        const uint64_t position,
+        unsigned char *result
+    );
+
     /// Compute a Sapling commitment.
     ///
     /// The `diversifier` parameter must be 11 bytes in length.

src/rustzcash.rs

@@ -33,6 +33,8 @@ use std::ffi::CStr;
 use std::fs::File;
 use std::slice;
 
+use sapling_crypto::primitives::ViewingKey;
+
 pub mod equihash;
 
 #[cfg(test)]
@@ -338,29 +340,27 @@ pub extern "system" fn librustzcash_sapling_generate_r(result: *mut [c_uchar; 32
         .expect("result must be 32 bytes");
 }
 
-/// Compute Sapling note commitment.
-#[no_mangle]
-pub extern "system" fn librustzcash_sapling_compute_cm(
+// Private utility function to get Note from C parameters
+fn priv_get_note(
     diversifier: *const [c_uchar; 11],
     pk_d: *const [c_uchar; 32],
     value: uint64_t,
     r: *const [c_uchar; 32],
-    result: *mut [c_uchar; 32],
-) -> bool {
+) -> Result<sapling_crypto::primitives::Note<Bls12>, ()> {
     let diversifier = sapling_crypto::primitives::Diversifier(unsafe { *diversifier });
     let g_d = match diversifier.g_d::<Bls12>(&JUBJUB) {
         Some(g_d) => g_d,
-        None => return false,
+        None => return Err(()),
     };
 
     let pk_d = match edwards::Point::<Bls12, Unknown>::read(&(unsafe { &*pk_d })[..], &JUBJUB) {
         Ok(p) => p,
-        Err(_) => return false,
+        Err(_) => return Err(()),
     };
 
     let pk_d = match pk_d.as_prime_order(&JUBJUB) {
         Some(pk_d) => pk_d,
-        None => return false,
+        None => return Err(()),
     };
 
     // Deserialize randomness
@@ -369,7 +369,7 @@ pub extern "system" fn librustzcash_sapling_compute_cm(
     repr.read_le(&r[..]).expect("length is not 32 bytes");
     let r = match Fs::from_repr(repr) {
         Ok(p) => p,
-        Err(_) => return false,
+        Err(_) => return Err(()),
     };
 
     let note = sapling_crypto::primitives::Note {
@@ -379,6 +379,68 @@ pub extern "system" fn librustzcash_sapling_compute_cm(
         r,
     };
 
+    Ok(note)
+}
+
+/// Compute Sapling note nullifier.
+#[no_mangle]
+pub extern "system" fn librustzcash_sapling_compute_nf(
+    diversifier: *const [c_uchar; 11],
+    pk_d: *const [c_uchar; 32],
+    value: uint64_t,
+    r: *const [c_uchar; 32],
+    ak: *const [c_uchar; 32],
+    nk: *const [c_uchar; 32],
+    position: uint64_t,
+    result: *mut [c_uchar; 32],
+) -> bool {
+    let note = match priv_get_note(diversifier, pk_d, value, r) {
+        Ok(p) => p,
+        Err(_) => return false,
+    };
+
+    let ak = match edwards::Point::<Bls12, Unknown>::read(&(unsafe { &*ak })[..], &JUBJUB) {
+        Ok(p) => p,
+        Err(_) => return false,
+    };
+
+    let ak = match ak.as_prime_order(&JUBJUB) {
+        Some(ak) => ak,
+        None => return false,
+    };
+
+    let nk = match edwards::Point::<Bls12, Unknown>::read(&(unsafe { &*nk })[..], &JUBJUB) {
+        Ok(p) => p,
+        Err(_) => return false,
+    };
+
+    let nk = match nk.as_prime_order(&JUBJUB) {
+        Some(nk) => nk,
+        None => return false,
+    };
+
+    let vk = ViewingKey { ak, nk };
+    let nf = note.nf(&vk, position, &JUBJUB);
+    let result = unsafe { &mut *result };
+    result.copy_from_slice(&nf);
+
+    true
+}
+
+/// Compute Sapling note commitment.
+#[no_mangle]
+pub extern "system" fn librustzcash_sapling_compute_cm(
+    diversifier: *const [c_uchar; 11],
+    pk_d: *const [c_uchar; 32],
+    value: uint64_t,
+    r: *const [c_uchar; 32],
+    result: *mut [c_uchar; 32],
+) -> bool {
+    let note = match priv_get_note(diversifier, pk_d, value, r) {
+        Ok(p) => p,
+        Err(_) => return false,
+    };
+
     let result = unsafe { &mut *result };
     write_le(note.cm(&JUBJUB).into_repr(), &mut result[..]);