Move mul and square operations on a elliptic curve to CurveGFp so we

can use different representations/operations depending on the curve
(eg, using a specialized version for P-256 reduction)

1 files changed, 122 insertions, 0 deletions

diff --git a/src/lib/math/ec_gfp/curve_gfp.cpp b/src/lib/math/ec_gfp/curve_gfp.cpp
new file mode 100644
index 000000000..2fa9f391e
--- /dev/null
+++ b/src/lib/math/ec_gfp/curve_gfp.cpp
@@ -0,0 +1,122 @@
+/*
+* Elliptic curves over GF(p) Montgomery Representation
+* (C) 2014 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/curve_gfp.h>
+#include <botan/internal/mp_core.h>
+
+namespace Botan {
+
+namespace {
+
+class CurveGFp_Montgomery : public CurveGFp_Repr
+   {
+   public:
+      CurveGFp_Montgomery(const BigInt& p, const BigInt& a, const BigInt& b) :
+         m_p(p), m_a(a), m_b(b),
+         m_p_words(m_p.sig_words()),
+         m_p_dash(monty_inverse(m_p.word_at(0)))
+         {
+         const BigInt r = BigInt::power_of_2(m_p_words * BOTAN_MP_WORD_BITS);
+
+         m_r2  = (r * r) % p;
+         m_a_r = (m_a * r) % p;
+         m_b_r = (m_b * r) % p;
+         }
+
+      const BigInt& get_a() const override { return m_a; }
+
+      const BigInt& get_b() const override { return m_b; }
+
+      const BigInt& get_p() const override { return m_p; }
+
+      const BigInt& get_a_rep() const override { return m_a_r; }
+
+      const BigInt& get_b_rep() const override { return m_b_r; }
+
+      void to_curve_rep(BigInt& x, secure_vector<word>& ws) const override;
+
+      void from_curve_rep(BigInt& x, secure_vector<word>& ws) const override;
+
+      void curve_mul(BigInt& z, const BigInt& x, const BigInt& y,
+                     secure_vector<word>& ws) const override;
+
+      void curve_sqr(BigInt& z, const BigInt& x,
+                     secure_vector<word>& ws) const override;
+   private:
+      BigInt m_p, m_a, m_b;
+      size_t m_p_words; // cache of m_p.sig_words()
+
+      // Montgomery parameters
+      BigInt m_r2, m_a_r, m_b_r;
+      word m_p_dash;
+   };
+
+void CurveGFp_Montgomery::to_curve_rep(BigInt& x, secure_vector<word>& ws) const
+   {
+   const BigInt tx = x;
+   curve_mul(x, tx, m_r2, ws);
+   }
+
+void CurveGFp_Montgomery::from_curve_rep(BigInt& x, secure_vector<word>& ws) const
+   {
+   const BigInt tx = x;
+   curve_mul(x, tx, 1, ws);
+   }
+
+void CurveGFp_Montgomery::curve_mul(BigInt& z, const BigInt& x, const BigInt& y,
+                                    secure_vector<word>& ws) const
+   {
+   if(x.is_zero() || y.is_zero())
+      {
+      z = 0;
+      return;
+      }
+
+   const size_t output_size = 2*m_p_words + 1;
+   ws.resize(2*(m_p_words+2));
+
+   z.grow_to(output_size);
+   z.clear();
+
+   bigint_monty_mul(z.mutable_data(), output_size,
+                    x.data(), x.size(), x.sig_words(),
+                    y.data(), y.size(), y.sig_words(),
+                    m_p.data(), m_p_words, m_p_dash,
+                    &ws[0]);
+   }
+
+void CurveGFp_Montgomery::curve_sqr(BigInt& z, const BigInt& x,
+                                    secure_vector<word>& ws) const
+   {
+   if(x.is_zero())
+      {
+      z = 0;
+      return;
+      }
+
+   const size_t output_size = 2*m_p_words + 1;
+
+   ws.resize(2*(m_p_words+2));
+
+   z.grow_to(output_size);
+   z.clear();
+
+   bigint_monty_sqr(z.mutable_data(), output_size,
+                    x.data(), x.size(), x.sig_words(),
+                    m_p.data(), m_p_words, m_p_dash,
+                    &ws[0]);
+   }
+
+}
+
+std::shared_ptr<CurveGFp_Repr>
+CurveGFp::choose_repr(const BigInt& p, const BigInt& a, const BigInt& b)
+   {
+   return std::shared_ptr<CurveGFp_Repr>(new CurveGFp_Montgomery(p, a, b));
+   }
+
+}