Expose reduction mod p in CurveGFp

This is slightly slower for Brainpool, but NIST curves are 5% faster.

3 files changed, 28 insertions, 16 deletions

diff --git a/src/lib/pubkey/ec_group/curve_gfp.cpp b/src/lib/pubkey/ec_group/curve_gfp.cpp
index 8ce8a6732..bd68a3ed7 100644
--- a/src/lib/pubkey/ec_group/curve_gfp.cpp
+++ b/src/lib/pubkey/ec_group/curve_gfp.cpp
@@ -60,6 +60,8 @@ 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;
@@ -91,6 +93,11 @@ 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?
@@ -195,10 +202,10 @@ class CurveGFp_NIST : public CurveGFp_Repr
       bool is_one(const BigInt& x) const override { return x == 1; }
 
       void to_curve_rep(BigInt& x, secure_vector<word>& ws) const override
-         { redc(x, ws); }
+         { redc_mod_p(x, ws); }
 
       void from_curve_rep(BigInt& x, secure_vector<word>& ws) const override
-         { redc(x, ws); }
+         { redc_mod_p(x, ws); }
 
       BigInt invert_element(const BigInt& x, secure_vector<word>& ws) const override;
 
@@ -225,8 +232,6 @@ class CurveGFp_NIST : public CurveGFp_Repr
                            size_t x_size,
                            secure_vector<word>& ws) const override;
    private:
-      virtual void redc(BigInt& x, secure_vector<word>& ws) const = 0;
-
       // Curve parameters
       BigInt m_1;
       BigInt m_a, m_b;
@@ -259,7 +264,7 @@ void CurveGFp_NIST::curve_mul_words(BigInt& z,
               y.data(), y.size(), std::min(m_p_words, y.size()),
               ws.data(), ws.size());
 
-   this->redc(z, ws);
+   this->redc_mod_p(z, ws);
    }
 
 void CurveGFp_NIST::curve_sqr_words(BigInt& z, const word x[], size_t x_size,
@@ -276,7 +281,7 @@ void CurveGFp_NIST::curve_sqr_words(BigInt& z, const word x[], size_t x_size,
               x, x_size, std::min(m_p_words, x_size),
               ws.data(), ws.size());
 
-   this->redc(z, ws);
+   this->redc_mod_p(z, ws);
    }
 
 #if defined(BOTAN_HAS_NIST_PRIME_REDUCERS_W32)
@@ -290,7 +295,7 @@ class CurveGFp_P192 final : public CurveGFp_NIST
       CurveGFp_P192(const BigInt& a, const BigInt& b) : CurveGFp_NIST(192, a, b) {}
       const BigInt& get_p() const override { return prime_p192(); }
    private:
-      void redc(BigInt& x, secure_vector<word>& ws) const override { redc_p192(x, ws); }
+      void redc_mod_p(BigInt& x, secure_vector<word>& ws) const override { redc_p192(x, ws); }
    };
 
 /**
@@ -302,7 +307,7 @@ class CurveGFp_P224 final : public CurveGFp_NIST
       CurveGFp_P224(const BigInt& a, const BigInt& b) : CurveGFp_NIST(224, a, b) {}
       const BigInt& get_p() const override { return prime_p224(); }
    private:
-      void redc(BigInt& x, secure_vector<word>& ws) const override { redc_p224(x, ws); }
+      void redc_mod_p(BigInt& x, secure_vector<word>& ws) const override { redc_p224(x, ws); }
    };
 
 /**
@@ -314,7 +319,7 @@ class CurveGFp_P256 final : public CurveGFp_NIST
       CurveGFp_P256(const BigInt& a, const BigInt& b) : CurveGFp_NIST(256, a, b) {}
       const BigInt& get_p() const override { return prime_p256(); }
    private:
-      void redc(BigInt& x, secure_vector<word>& ws) const override { redc_p256(x, ws); }
+      void redc_mod_p(BigInt& x, secure_vector<word>& ws) const override { redc_p256(x, ws); }
       BigInt invert_element(const BigInt& x, secure_vector<word>& ws) const override;
    };
 
@@ -389,7 +394,7 @@ class CurveGFp_P384 final : public CurveGFp_NIST
       CurveGFp_P384(const BigInt& a, const BigInt& b) : CurveGFp_NIST(384, a, b) {}
       const BigInt& get_p() const override { return prime_p384(); }
    private:
-      void redc(BigInt& x, secure_vector<word>& ws) const override { redc_p384(x, ws); }
+      void redc_mod_p(BigInt& x, secure_vector<word>& ws) const override { redc_p384(x, ws); }
       BigInt invert_element(const BigInt& x, secure_vector<word>& ws) const override;
    };
 
@@ -475,7 +480,7 @@ class CurveGFp_P521 final : public CurveGFp_NIST
       CurveGFp_P521(const BigInt& a, const BigInt& b) : CurveGFp_NIST(521, a, b) {}
       const BigInt& get_p() const override { return prime_p521(); }
    private:
-      void redc(BigInt& x, secure_vector<word>& ws) const override { redc_p521(x, ws); }
+      void redc_mod_p(BigInt& x, secure_vector<word>& ws) const override { redc_p521(x, ws); }
       BigInt invert_element(const BigInt& x, secure_vector<word>& ws) const override;
    };
 
diff --git a/src/lib/pubkey/ec_group/curve_gfp.h b/src/lib/pubkey/ec_group/curve_gfp.h
index 85640b442..338b524e8 100644
--- a/src/lib/pubkey/ec_group/curve_gfp.h
+++ b/src/lib/pubkey/ec_group/curve_gfp.h
@@ -49,6 +49,8 @@ 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;
@@ -169,6 +171,11 @@ 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 4c048427f..77803de78 100644
--- a/src/lib/pubkey/ec_group/point_gfp.cpp
+++ b/src/lib/pubkey/ec_group/point_gfp.cpp
@@ -304,14 +304,14 @@ void PointGFp::mult2(std::vector<BigInt>& ws_bn)
 
    m_curve.mul(T1, m_coord_x, T0, ws);
    T1 <<= 2; // * 4
-   T1.reduce_below(p, sub_ws);
+   m_curve.redc_mod_p(T1, 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
-      T4.reduce_below(p, sub_ws);
+      m_curve.redc_mod_p(T4, sub_ws);
       }
    else if(m_curve.a_is_minus_3())
       {
@@ -331,7 +331,7 @@ 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)
-      T4.reduce_below(p, sub_ws);
+      m_curve.redc_mod_p(T4, sub_ws);
       }
    else
       {
@@ -350,7 +350,7 @@ void PointGFp::mult2(std::vector<BigInt>& ws_bn)
 
    m_curve.sqr(T3, T0, ws);
    T3 <<= 3;
-   T3.reduce_below(p, sub_ws);
+   m_curve.redc_mod_p(T3, sub_ws);
 
    T1.mod_sub(T2, p, sub_ws);
 
@@ -361,7 +361,7 @@ void PointGFp::mult2(std::vector<BigInt>& ws_bn)
 
    m_curve.mul(T2, m_coord_y, m_coord_z, ws);
    T2 <<= 1;
-   T2.reduce_below(p, sub_ws);
+   m_curve.redc_mod_p(T2, sub_ws);
 
    m_coord_y = T0;
    m_coord_z = T2;