Add blinded_base_point_multiply_x

Often useful when the point is not needed

2 files changed, 20 insertions, 0 deletions

diff --git a/src/lib/pubkey/ec_group/ec_group.cpp b/src/lib/pubkey/ec_group/ec_group.cpp
index 723a4148e..5fb79c923 100644
--- a/src/lib/pubkey/ec_group/ec_group.cpp
+++ b/src/lib/pubkey/ec_group/ec_group.cpp
@@ -483,6 +483,13 @@ PointGFp EC_Group::blinded_base_point_multiply(const BigInt& k,
    return data().blinded_base_point_multiply(k, rng, ws);
    }
 
+BigInt EC_Group::blinded_base_point_multiply_x(const BigInt& k,
+                                               RandomNumberGenerator& rng,
+                                               std::vector<BigInt>& ws) const
+   {
+   return data().blinded_base_point_multiply(k, rng, ws).get_affine_x();
+   }
+
 PointGFp EC_Group::blinded_var_point_multiply(const PointGFp& point,
                                               const BigInt& k,
                                               RandomNumberGenerator& rng,
diff --git a/src/lib/pubkey/ec_group/ec_group.h b/src/lib/pubkey/ec_group/ec_group.h
index 8238c2902..47652e1b4 100644
--- a/src/lib/pubkey/ec_group/ec_group.h
+++ b/src/lib/pubkey/ec_group/ec_group.h
@@ -248,6 +248,19 @@ class BOTAN_PUBLIC_API(2,0) EC_Group final
 
       /**
       * Blinded point multiplication, attempts resistance to side channels
+      * Returns just the x coordinate of the point
+      *
+      * @param k the scalar
+      * @param rng a random number generator
+      * @param ws a temp workspace
+      * @return x coordinate of base_point*k
+      */
+      BigInt blinded_base_point_multiply_x(const BigInt& k,
+                                           RandomNumberGenerator& rng,
+                                           std::vector<BigInt>& ws) const;
+
+      /**
+      * Blinded point multiplication, attempts resistance to side channels
       * @param point input point
       * @param k the scalar
       * @param rng a random number generator