Only pass a single prior child

src/fcmp/curve_trees.cpp

@@ -44,22 +44,20 @@ template class CurveTrees<Helios, Selene>;
 template<typename C>
 typename C::Point get_new_parent(const C &curve, const typename C::Chunk &new_children)
 {
-    // New parent means no prior children, fill priors with 0
-    std::vector<typename C::Scalar> prior_children;
-    tower_cycle::extend_zeroes(curve, new_children.len, prior_children);
-
     return curve.hash_grow(
             curve.m_hash_init_point,
             0,/*offset*/
-            typename C::Chunk{prior_children.data(), prior_children.size()},
+            curve.zero_scalar(),
             new_children
         );
 };
+template Helios::Point get_new_parent<Helios>(const Helios &curve, const typename Helios::Chunk &new_children);
+template Selene::Point get_new_parent<Selene>(const Selene &curve, const typename Selene::Chunk &new_children);
 //----------------------------------------------------------------------------------------------------------------------
 //----------------------------------------------------------------------------------------------------------------------
 // Static functions
 //----------------------------------------------------------------------------------------------------------------------
-// Hash the first chunk of children being added to a layer
+// Hash the first chunk of the children now being added to a layer
 template<typename C>
 static typename C::Point get_first_parent(const C &curve,
     const typename C::Chunk &new_children,
@@ -72,21 +70,17 @@ static typename C::Point get_first_parent(const C &curve,
     if (last_chunk_ptr == nullptr)
         return get_new_parent<C>(curve, new_children);
 
-    std::vector<typename C::Scalar> prior_children;
+    typename C::Scalar first_child_after_offset = curve.zero_scalar();
+
     if (child_layer_last_hash_updated)
     {
         // If the last chunk has updated children in it, then we need to get the delta to the old children
-        prior_children.emplace_back(last_chunk_ptr->last_child);
+        first_child_after_offset = last_chunk_ptr->last_child;
-
-        // Extend prior children by zeroes for any additional new children, since they must be new
-        if (new_children.len > 1)
-            tower_cycle::extend_zeroes(curve, new_children.len - 1, prior_children);
     }
     else if (offset > 0)
     {
         // If we're updating the parent hash and no children were updated, then we're just adding new children
-        // to the existing last chunk and can fill priors with 0
+        // to the existing last chunk and can leave first_child_after_offset as zero
-        tower_cycle::extend_zeroes(curve, new_children.len, prior_children);
     }
     else
     {
@@ -97,7 +91,7 @@ static typename C::Point get_first_parent(const C &curve,
     return curve.hash_grow(
             last_chunk_ptr->last_parent,
             offset,
-            typename C::Chunk{prior_children.data(), prior_children.size()},
+            first_child_after_offset,
             new_children
         );
 };

src/fcmp/fcmp_rust/Cargo.lock

@@ -71,7 +71,7 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 [[package]]
 name = "ciphersuite"
 version = "0.4.1"
-source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a17500708f5c6d79ec9cc33d53c771149db152c3"
+source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a11db094aac0384b9e62930f6f9f0d062d436897"
 dependencies = [
  "blake2",
  "dalek-ff-group",
@@ -161,7 +161,7 @@ dependencies = [
 [[package]]
 name = "dalek-ff-group"
 version = "0.4.1"
-source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a17500708f5c6d79ec9cc33d53c771149db152c3"
+source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a11db094aac0384b9e62930f6f9f0d062d436897"
 dependencies = [
  "crypto-bigint",
  "curve25519-dalek",
@@ -198,7 +198,7 @@ dependencies = [
 [[package]]
 name = "ec-divisors"
 version = "0.1.0"
-source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a17500708f5c6d79ec9cc33d53c771149db152c3"
+source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a11db094aac0384b9e62930f6f9f0d062d436897"
 dependencies = [
  "dalek-ff-group",
  "group",
@@ -272,7 +272,7 @@ checksum = "28dea519a9695b9977216879a3ebfddf92f1c08c05d984f8996aecd6ecdc811d"
 [[package]]
 name = "flexible-transcript"
 version = "0.3.2"
-source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a17500708f5c6d79ec9cc33d53c771149db152c3"
+source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a11db094aac0384b9e62930f6f9f0d062d436897"
 dependencies = [
  "blake2",
  "digest",
@@ -285,7 +285,7 @@ dependencies = [
 [[package]]
 name = "full-chain-membership-proofs"
 version = "0.1.0"
-source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a17500708f5c6d79ec9cc33d53c771149db152c3"
+source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a11db094aac0384b9e62930f6f9f0d062d436897"
 dependencies = [
  "ciphersuite",
  "ec-divisors",
@@ -305,7 +305,7 @@ checksum = "e6d5a32815ae3f33302d95fdcb2ce17862f8c65363dcfd29360480ba1001fc9c"
 [[package]]
 name = "generalized-bulletproofs"
 version = "0.1.0"
-source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a17500708f5c6d79ec9cc33d53c771149db152c3"
+source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a11db094aac0384b9e62930f6f9f0d062d436897"
 dependencies = [
  "ciphersuite",
  "flexible-transcript",
@@ -368,7 +368,7 @@ dependencies = [
 [[package]]
 name = "helioselene"
 version = "0.1.0"
-source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a17500708f5c6d79ec9cc33d53c771149db152c3"
+source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a11db094aac0384b9e62930f6f9f0d062d436897"
 dependencies = [
  "crypto-bigint",
  "dalek-ff-group",
@@ -429,7 +429,7 @@ dependencies = [
 [[package]]
 name = "minimal-ed448"
 version = "0.4.0"
-source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a17500708f5c6d79ec9cc33d53c771149db152c3"
+source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a11db094aac0384b9e62930f6f9f0d062d436897"
 dependencies = [
  "crypto-bigint",
  "ff",
@@ -444,7 +444,7 @@ dependencies = [
 [[package]]
 name = "multiexp"
 version = "0.4.0"
-source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a17500708f5c6d79ec9cc33d53c771149db152c3"
+source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a11db094aac0384b9e62930f6f9f0d062d436897"
 dependencies = [
  "ff",
  "group",
@@ -613,7 +613,7 @@ dependencies = [
 [[package]]
 name = "std-shims"
 version = "0.1.1"
-source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a17500708f5c6d79ec9cc33d53c771149db152c3"
+source = "git+https://github.com/kayabaNerve/fcmp-plus-plus#a11db094aac0384b9e62930f6f9f0d062d436897"
 dependencies = [
  "hashbrown",
  "spin",
@@ -627,9 +627,9 @@ checksum = "81cdd64d312baedb58e21336b31bc043b77e01cc99033ce76ef539f78e965ebc"
 
 [[package]]
 name = "syn"
-version = "2.0.65"
+version = "2.0.66"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d2863d96a84c6439701d7a38f9de935ec562c8832cc55d1dde0f513b52fad106"
+checksum = "c42f3f41a2de00b01c0aaad383c5a45241efc8b2d1eda5661812fda5f3cdcff5"
 dependencies = [
  "proc-macro2",
  "quote",

src/fcmp/fcmp_rust/fcmp++.h

@@ -113,12 +113,12 @@ SeleneScalar selene_zero_scalar();
 
 CResult<HeliosPoint> hash_grow_helios(HeliosPoint existing_hash,
                                              uintptr_t offset,
-                                             HeliosScalarSlice prior_children,
+                                             HeliosScalar first_child_after_offset,
                                              HeliosScalarSlice new_children);
 
 CResult<SelenePoint> hash_grow_selene(SelenePoint existing_hash,
                                              uintptr_t offset,
-                                             SeleneScalarSlice prior_children,
+                                             SeleneScalar first_child_after_offset,
                                              SeleneScalarSlice new_children);
 
 } // extern "C"

src/fcmp/fcmp_rust/src/lib.rs

@@ -79,12 +79,11 @@ pub extern "C" fn selene_point_to_bytes(selene_point: SelenePoint) -> *const u8
 }
 
 // Get the x coordinate of the ed25519 point
-// TODO: Move this to C++
 #[allow(clippy::not_unsafe_ptr_arg_deref)]
 #[no_mangle]
 pub extern "C" fn ed25519_point_to_selene_scalar(ed25519_point: *const u8) -> SeleneScalar {
     let mut ed25519_point = unsafe { core::slice::from_raw_parts(ed25519_point, 32) };
-    // TODO: If not moved to C++, at least return an error here (instead of unwrapping)
+    // TODO: Return an error here (instead of unwrapping)
     let ed25519_point = <Ed25519>::read_G(&mut ed25519_point).unwrap();
 
     let xy_coords = <Ed25519 as Ciphersuite>::G::to_xy(ed25519_point);
@@ -153,14 +152,14 @@ impl<T, E> CResult<T, E> {
 pub extern "C" fn hash_grow_helios(
     existing_hash: HeliosPoint,
     offset: usize,
-    prior_children: HeliosScalarSlice,
+    first_child_after_offset: HeliosScalar,
     new_children: HeliosScalarSlice,
 ) -> CResult<HeliosPoint, io::Error> {
     let hash = hash_grow(
         helios_generators(),
         existing_hash,
         offset,
-        prior_children.into(),
+        first_child_after_offset,
         new_children.into(),
     );
 
@@ -178,14 +177,14 @@ pub extern "C" fn hash_grow_helios(
 pub extern "C" fn hash_grow_selene(
     existing_hash: SelenePoint,
     offset: usize,
-    prior_children: SeleneScalarSlice,
+    first_child_after_offset: SeleneScalar,
     new_children: SeleneScalarSlice,
 ) -> CResult<SelenePoint, io::Error> {
     let hash = hash_grow(
         selene_generators(),
         existing_hash,
         offset,
-        prior_children.into(),
+        first_child_after_offset,
         new_children.into(),
     );
 

src/fcmp/tower_cycle.cpp

@@ -48,13 +48,13 @@ Selene::CycleScalar Selene::point_to_cycle_scalar(const Selene::Point &point) co
 Helios::Point Helios::hash_grow(
     const Helios::Point &existing_hash,
     const std::size_t offset,
-    const Helios::Chunk &prior_children,
+    const Helios::Scalar &first_child_after_offset,
     const Helios::Chunk &new_children) const
 {
     auto res = fcmp_rust::hash_grow_helios(
         existing_hash,
         offset,
-        prior_children,
+        first_child_after_offset,
         new_children);
     if (res.err != 0) {
       throw std::runtime_error("failed to hash grow");
@@ -65,13 +65,13 @@ Helios::Point Helios::hash_grow(
 Selene::Point Selene::hash_grow(
     const Selene::Point &existing_hash,
     const std::size_t offset,
-    const Selene::Chunk &prior_children,
+    const Selene::Scalar &first_child_after_offset,
     const Selene::Chunk &new_children) const
 {
     auto res = fcmp_rust::hash_grow_selene(
         existing_hash,
         offset,
-        prior_children,
+        first_child_after_offset,
         new_children);
     if (res.err != 0) {
       throw std::runtime_error("failed to hash grow");
@@ -150,6 +150,10 @@ std::string Selene::to_string(const typename Selene::Point &point) const
 //----------------------------------------------------------------------------------------------------------------------
 SeleneScalar ed_25519_point_to_scalar(const crypto::ec_point &point)
 {
+    // If this function receives the ec_point, this is fine
+    // If this function can receive a decompressed point, it'd be notably faster
+    // to extract the Wei25519 x coordinate from the C side of things and then
+    // pass that
     return fcmp_rust::ed25519_point_to_selene_scalar((uint8_t*) &point.data);
 }
 //----------------------------------------------------------------------------------------------------------------------
@@ -182,7 +186,6 @@ void extend_scalars_from_cycle_points(const C_POINTS &curve,
 
     for (const auto &point : points)
     {
-        // TODO: implement reading just the x coordinate of points on curves in curve cycle in C/C++
         typename C_SCALARS::Scalar scalar = curve.point_to_cycle_scalar(point);
         scalars_out.push_back(std::move(scalar));
     }

src/fcmp/tower_cycle.h

@@ -82,7 +82,7 @@ public:
     virtual typename C::Point hash_grow(
         const typename C::Point &existing_hash,
         const std::size_t offset,
-        const typename C::Chunk &prior_children,
+        const typename C::Scalar &first_child_after_offset,
         const typename C::Chunk &new_children) const = 0;
 
     virtual typename C::Scalar zero_scalar() const = 0;
@@ -120,7 +120,7 @@ public:
     Point hash_grow(
         const Point &existing_hash,
         const std::size_t offset,
-        const Chunk &prior_children,
+        const Scalar &first_child_after_offset,
         const Chunk &new_children) const override;
 
     Scalar zero_scalar() const override;
@@ -154,7 +154,7 @@ public:
     Point hash_grow(
         const Point &existing_hash,
         const std::size_t offset,
-        const Chunk &prior_children,
+        const Scalar &first_child_after_offset,
         const Chunk &new_children) const override;
 
     Scalar zero_scalar() const override;