Add BigInt::mod_mul

3 files changed, 10 insertions, 27 deletions

diff --git a/src/lib/pubkey/ec_group/curve_gfp.cpp b/src/lib/pubkey/ec_group/curve_gfp.cpp
index bd68a3ed7..f2f5607e1 100644
--- a/src/lib/pubkey/ec_group/curve_gfp.cpp
+++ b/src/lib/pubkey/ec_group/curve_gfp.cpp
@@ -60,8 +60,6 @@ class CurveGFp_Montgomery final : public CurveGFp_Repr
 
       size_t get_ws_size() const override { return 2*m_p_words + 4; }
 
-      void redc_mod_p(BigInt& z, secure_vector<word>& ws) const override;
-
       BigInt invert_element(const BigInt& x, secure_vector<word>& ws) const override;
 
       void to_curve_rep(BigInt& x, secure_vector<word>& ws) const override;
@@ -93,11 +91,6 @@ class CurveGFp_Montgomery final : public CurveGFp_Repr
       bool m_a_is_minus_3;
    };
 
-void CurveGFp_Montgomery::redc_mod_p(BigInt& z, secure_vector<word>& ws) const
-   {
-   z.reduce_below(m_p, ws);
-   }
-
 BigInt CurveGFp_Montgomery::invert_element(const BigInt& x, secure_vector<word>& ws) const
    {
    // Should we use Montgomery inverse instead?
@@ -207,6 +200,8 @@ class CurveGFp_NIST : public CurveGFp_Repr
       void from_curve_rep(BigInt& x, secure_vector<word>& ws) const override
          { redc_mod_p(x, ws); }
 
+      virtual void redc_mod_p(BigInt& z, secure_vector<word>& ws) const = 0;
+
       BigInt invert_element(const BigInt& x, secure_vector<word>& ws) const override;
 
       void curve_mul_words(BigInt& z,
diff --git a/src/lib/pubkey/ec_group/curve_gfp.h b/src/lib/pubkey/ec_group/curve_gfp.h
index d03247244..fe7a0a54d 100644
--- a/src/lib/pubkey/ec_group/curve_gfp.h
+++ b/src/lib/pubkey/ec_group/curve_gfp.h
@@ -49,8 +49,6 @@ class BOTAN_UNSTABLE_API CurveGFp_Repr
       */
       virtual const BigInt& get_1_rep() const = 0;
 
-      virtual void redc_mod_p(BigInt& z, secure_vector<word>& ws) const = 0;
-
       virtual BigInt invert_element(const BigInt& x, secure_vector<word>& ws) const = 0;
 
       virtual void to_curve_rep(BigInt& x, secure_vector<word>& ws) const = 0;
@@ -171,11 +169,6 @@ class BOTAN_UNSTABLE_API CurveGFp final
 
       // TODO: from_rep taking && ref
 
-      void redc_mod_p(BigInt& z, secure_vector<word>& ws) const
-         {
-         m_repr->redc_mod_p(z, ws);
-         }
-
       void mul(BigInt& z, const BigInt& x, const BigInt& y, secure_vector<word>& ws) const
          {
          m_repr->curve_mul(z, x, y, ws);
diff --git a/src/lib/pubkey/ec_group/point_gfp.cpp b/src/lib/pubkey/ec_group/point_gfp.cpp
index 7bc6c4975..b4b3871cb 100644
--- a/src/lib/pubkey/ec_group/point_gfp.cpp
+++ b/src/lib/pubkey/ec_group/point_gfp.cpp
@@ -2,7 +2,7 @@
 * Point arithmetic on elliptic curves over GF(p)
 *
 * (C) 2007 Martin Doering, Christoph Ludwig, Falko Strenzke
-*     2008-2011,2012,2014,2015 Jack Lloyd
+*     2008-2011,2012,2014,2015,2018 Jack Lloyd
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
@@ -152,6 +152,7 @@ void PointGFp::add_affine(const word x_words[], size_t x_size,
 
    m_curve.sqr(m_coord_x, T0, ws);
    m_coord_x.mod_sub(T1, p, sub_ws);
+
    m_coord_x.mod_sub(T3, p, sub_ws);
    m_coord_x.mod_sub(T3, p, sub_ws);
 
@@ -303,15 +304,13 @@ void PointGFp::mult2(std::vector<BigInt>& ws_bn)
    m_curve.sqr(T0, m_coord_y, ws);
 
    m_curve.mul(T1, m_coord_x, T0, ws);
-   T1 <<= 2; // * 4
-   m_curve.redc_mod_p(T1, sub_ws);
+   T1.mod_mul(4, p, sub_ws);
 
    if(m_curve.a_is_zero())
       {
       // if a == 0 then 3*x^2 + a*z^4 is just 3*x^2
       m_curve.sqr(T4, m_coord_x, ws); // x^2
-      T4 *= 3; // 3*x^2
-      m_curve.redc_mod_p(T4, sub_ws);
+      T4.mod_mul(3, p, sub_ws); // 3*x^2
       }
    else if(m_curve.a_is_minus_3())
       {
@@ -330,8 +329,7 @@ void PointGFp::mult2(std::vector<BigInt>& ws_bn)
 
       m_curve.mul(T4, T2, T3, ws); // (x-z^2)*(x+z^2)
 
-      T4 *= 3; // 3*(x-z^2)*(x+z^2)
-      m_curve.redc_mod_p(T4, sub_ws);
+      T4.mod_mul(3, p, sub_ws); // 3*(x-z^2)*(x+z^2)
       }
    else
       {
@@ -340,8 +338,7 @@ void PointGFp::mult2(std::vector<BigInt>& ws_bn)
       m_curve.mul(T3, m_curve.get_a_rep(), T4, ws); // a*z^4
 
       m_curve.sqr(T4, m_coord_x, ws); // x^2
-      T4 *= 3; // 3*x^2
-      T4.reduce_below(p, sub_ws);
+      T4.mod_mul(3, p, sub_ws);
       T4.mod_add(T3, p, sub_ws); // 3*x^2 + a*z^4
       }
 
@@ -350,8 +347,7 @@ void PointGFp::mult2(std::vector<BigInt>& ws_bn)
    T2.mod_sub(T1, p, sub_ws);
 
    m_curve.sqr(T3, T0, ws);
-   T3 <<= 3;
-   m_curve.redc_mod_p(T3, sub_ws);
+   T3.mod_mul(8, p, sub_ws);
 
    T1.mod_sub(T2, p, sub_ws);
 
@@ -361,8 +357,7 @@ void PointGFp::mult2(std::vector<BigInt>& ws_bn)
    m_coord_x = T2;
 
    m_curve.mul(T2, m_coord_y, m_coord_z, ws);
-   T2 <<= 1;
-   m_curve.redc_mod_p(T2, sub_ws);
+   T2.mod_mul(2, p, sub_ws);
 
    m_coord_y = T0;
    m_coord_z = T2;