Add random_element to affine element.

AztecProtocol · Apr 16, 2023 · 3dddda9 · 3dddda9
1 parent 540bb3a
commit 3dddda9
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diff --git a/cpp/src/barretenberg/ecc/groups/affine_element.hpp b/cpp/src/barretenberg/ecc/groups/affine_element.hpp
@@ -49,6 +49,13 @@ template <typename Fq, typename Fr, typename Params> class alignas(64) affine_el
 
     constexpr bool on_curve() const noexcept;
 
+    /**
+     * @brief Samples a random point on the curve.
+     *
+     * @return A randomly chosen point on the curve
+     */
+    static affine_element random_element(numeric::random::Engine* engine = nullptr) noexcept;
+
     /**
      * @brief Hash a seed value to curve.
      *

diff --git a/cpp/src/barretenberg/ecc/groups/affine_element_impl.hpp b/cpp/src/barretenberg/ecc/groups/affine_element_impl.hpp
@@ -202,5 +202,26 @@ affine_element<Fq, Fr, T> affine_element<Fq, Fr, T>::hash_to_curve(const uint64_
 
     return affine_element<Fq, Fr, T>(x_out, y_out_);
 }
+
+template <typename Fq, typename Fr, typename T>
+affine_element<Fq, Fr, T> affine_element<Fq, Fr, T>::random_element(numeric::random::Engine* engine) noexcept
+{
+    bool found_one = false;
+    Fq yy;
+    Fq x;
+    Fq y;
+    while (!found_one) {
+        x = Fq::random_element(engine);
+        yy = x.sqr() * x + T::b;
+        if constexpr (T::has_a) {
+            yy += (x * T::a);
+        }
+        auto [found_root, y1] = yy.sqrt();
+        y = y1;
+        found_one = found_root;
+    }
+    return affine_element<Fq, Fr, T>(x, y);
+}
+
 } // namespace group_elements
 } // namespace barretenberg