/*

* Elliptic curves over GF(p) Montgomery Representation

* (C) 2014,2015,2018 Jack Lloyd

*     2016 Matthias Gierlings

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#include <botan/curve_gfp.h>

#include <botan/internal/curve_nistp.h>

#include <botan/numthry.h>

#include <botan/reducer.h>

#include <botan/internal/mp_core.h>

#include <botan/internal/monty.h>

namespace Botan {

namespace {

class CurveGFp_Montgomery final : 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)))

         {

         Modular_Reducer mod_p(m_p);

         m_r.set_bit(m_p_words * BOTAN_MP_WORD_BITS);

         m_r = mod_p.reduce(m_r);

         m_r2  = mod_p.square(m_r);

         m_r3  = mod_p.multiply(m_r, m_r2);

         m_a_r = mod_p.multiply(m_r, m_a);

         m_b_r = mod_p.multiply(m_r, m_b);

         m_a_is_zero = m_a.is_zero();

         m_a_is_minus_3 = (m_a + 3 == m_p);

         }

      bool a_is_zero() const override { return m_a_is_zero; }

      bool a_is_minus_3() const override { return m_a_is_minus_3; }

      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; }

      const BigInt& get_1_rep() const override { return m_r; }

      bool is_one(const BigInt& x) const override { return x == m_r; }

      size_t get_p_words() const override { return m_p_words; }

      size_t get_ws_size() const override { return 2*m_p_words + 4; }

      BigInt invert_element(const BigInt& x, secure_vector<word>& ws) const override;

      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_words(BigInt& z,

                           const word x_words[],

                           const size_t x_size,

                           const BigInt& y,

                           secure_vector<word>& ws) const override;

      void curve_sqr_words(BigInt& z,

                           const word x_words[],

                           size_t x_size,

                           secure_vector<word>& ws) const override;

   private:

      BigInt m_p;

      BigInt m_a, m_b;

      BigInt m_a_r, m_b_r;

      size_t m_p_words; // cache of m_p.sig_words()

      // Montgomery parameters

      BigInt m_r, m_r2, m_r3;

      word m_p_dash;

      bool m_a_is_zero;

      bool m_a_is_minus_3;

   };

BigInt CurveGFp_Montgomery::invert_element(const BigInt& x, secure_vector<word>& ws) const

   {

   // Should we use Montgomery inverse instead?

   const BigInt inv = inverse_mod(x, m_p);

   BigInt res;

   curve_mul(res, inv, m_r3, ws);

   return res;

   }

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& z, secure_vector<word>& ws) const

   {

   if(ws.size() < get_ws_size())

      ws.resize(get_ws_size());

   const size_t output_size = 2*m_p_words + 2;

   if(z.size() < output_size)

      z.grow_to(output_size);

   bigint_monty_redc(z.mutable_data(),

                     m_p.data(), m_p_words, m_p_dash,

                     ws.data(), ws.size());

   }

void CurveGFp_Montgomery::curve_mul_words(BigInt& z,

                                          const word x_w[],

                                          size_t x_size,

                                          const BigInt& y,

                                          secure_vector<word>& ws) const

   {

   BOTAN_DEBUG_ASSERT(y.sig_words() <= m_p_words);

   if(ws.size() < get_ws_size())

      ws.resize(get_ws_size());

   const size_t output_size = 2*m_p_words + 2;

   if(z.size() < output_size)

      z.grow_to(output_size);

   bigint_mul(z.mutable_data(), z.size(),

              x_w, x_size, std::min(m_p_words, x_size),

              y.data(), y.size(), std::min(m_p_words, y.size()),

              ws.data(), ws.size());

   bigint_monty_redc(z.mutable_data(),

                     m_p.data(), m_p_words, m_p_dash,

                     ws.data(), ws.size());

   }

void CurveGFp_Montgomery::curve_sqr_words(BigInt& z,

                                          const word x[],

                                          size_t x_size,

                                          secure_vector<word>& ws) const

   {

   if(ws.size() < get_ws_size())

      ws.resize(get_ws_size());

   const size_t output_size = 2*m_p_words + 2;

   if(z.size() < output_size)

      z.grow_to(output_size);

   bigint_sqr(z.mutable_data(), z.size(),

              x, x_size, std::min(m_p_words, x_size),

              ws.data(), ws.size());

   bigint_monty_redc(z.mutable_data(),

                     m_p.data(), m_p_words, m_p_dash,

                     ws.data(), ws.size());

   }

class CurveGFp_NIST : public CurveGFp_Repr

   {

   public:

      CurveGFp_NIST(size_t p_bits, const BigInt& a, const BigInt& b) :

         m_1(1), m_a(a), m_b(b), m_p_words((p_bits + BOTAN_MP_WORD_BITS - 1) / BOTAN_MP_WORD_BITS)

         {

         // All Solinas prime curves are assumed a == -3

         }

      bool a_is_zero() const override { return false; }

      bool a_is_minus_3() const override { return true; }

      const BigInt& get_a() const override { return m_a; }

      const BigInt& get_b() const override { return m_b; }

      const BigInt& get_1_rep() const override { return m_1; }

      size_t get_p_words() const override { return m_p_words; }

      size_t get_ws_size() const override { return 2*m_p_words + 4; }

      const BigInt& get_a_rep() const override { return m_a; }

      const BigInt& get_b_rep() const override { return m_b; }

      bool is_one(const BigInt& x) const override { return x == 1; }

      void to_curve_rep(BigInt& x, secure_vector<word>& ws) const override

         { redc_mod_p(x, ws); }

      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,

                           const word x_words[],

                           const size_t x_size,

                           const BigInt& y,

                           secure_vector<word>& ws) const override;

      void curve_mul_tmp(BigInt& x, const BigInt& y, BigInt& tmp, secure_vector<word>& ws) const

         {

         curve_mul(tmp, x, y, ws);

         x.swap(tmp);

         }

      void curve_sqr_tmp(BigInt& x, BigInt& tmp, secure_vector<word>& ws) const

         {

         curve_sqr(tmp, x, ws);

         x.swap(tmp);

         }

      void curve_sqr_words(BigInt& z,

                           const word x_words[],

                           size_t x_size,

                           secure_vector<word>& ws) const override;

   private:

      // Curve parameters

      BigInt m_1;

      BigInt m_a, m_b;

      size_t m_p_words; // cache of m_p.sig_words()

   };

BigInt CurveGFp_NIST::invert_element(const BigInt& x, secure_vector<word>& ws) const

   {

   BOTAN_UNUSED(ws);

   return inverse_mod(x, get_p());

   }

void CurveGFp_NIST::curve_mul_words(BigInt& z,

                                    const word x_w[],

                                    size_t x_size,

                                    const BigInt& y,

                                    secure_vector<word>& ws) const

   {

   BOTAN_DEBUG_ASSERT(y.sig_words() <= m_p_words);

   if(ws.size() < get_ws_size())

      ws.resize(get_ws_size());

   const size_t output_size = 2*m_p_words + 2;

   if(z.size() < output_size)

      z.grow_to(output_size);

   bigint_mul(z.mutable_data(), z.size(),

              x_w, x_size, std::min(m_p_words, x_size),

              y.data(), y.size(), std::min(m_p_words, y.size()),

              ws.data(), ws.size());

   this->redc_mod_p(z, ws);

   }

void CurveGFp_NIST::curve_sqr_words(BigInt& z, const word x[], size_t x_size,

                                    secure_vector<word>& ws) const

   {

   if(ws.size() < get_ws_size())

      ws.resize(get_ws_size());

   const size_t output_size = 2*m_p_words + 2;

   if(z.size() < output_size)

      z.grow_to(output_size);

   bigint_sqr(z.mutable_data(), output_size,

              x, x_size, std::min(m_p_words, x_size),

              ws.data(), ws.size());

   this->redc_mod_p(z, ws);

   }

/**

* The NIST P-192 curve

*/

class CurveGFp_P192 final : public CurveGFp_NIST

   {

   public:

      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_mod_p(BigInt& x, secure_vector<word>& ws) const override { redc_p192(x, ws); }

   };

/**

* The NIST P-224 curve

*/

class CurveGFp_P224 final : public CurveGFp_NIST

   {

   public:

      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_mod_p(BigInt& x, secure_vector<word>& ws) const override { redc_p224(x, ws); }

   };

/**

* The NIST P-256 curve

*/

class CurveGFp_P256 final : public CurveGFp_NIST

   {

   public:

      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_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;

   };

BigInt CurveGFp_P256::invert_element(const BigInt& x, secure_vector<word>& ws) const

   {

   BigInt r, p2, p4, p8, p16, p32, tmp;

   curve_sqr(r, x, ws);

   curve_mul(p2, r, x, ws);

   curve_sqr(r, p2, ws);

   curve_sqr_tmp(r, tmp, ws);

   curve_mul(p4, r, p2, ws);

   curve_sqr(r, p4, ws);

   for(size_t i = 0; i != 3; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul(p8, r, p4, ws);

   curve_sqr(r, p8, ws);

   for(size_t i = 0; i != 7; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul(p16, r, p8, ws);

   curve_sqr(r, p16, ws);

   for(size_t i = 0; i != 15; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul(p32, r, p16, ws);

   curve_sqr(r, p32, ws);

   for(size_t i = 0; i != 31; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x, tmp, ws);

   for(size_t i = 0; i != 32*4; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, p32, tmp, ws);

   for(size_t i = 0; i != 32; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, p32, tmp, ws);

   for(size_t i = 0; i != 16; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, p16, tmp, ws);

   for(size_t i = 0; i != 8; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, p8, tmp, ws);

   for(size_t i = 0; i != 4; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, p4, tmp, ws);

   for(size_t i = 0; i != 2; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, p2, tmp, ws);

   for(size_t i = 0; i != 2; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x, tmp, ws);

   return r;

   }

/**

* The NIST P-384 curve

*/

class CurveGFp_P384 final : public CurveGFp_NIST

   {

   public:

      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_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;

   };

BigInt CurveGFp_P384::invert_element(const BigInt& x, secure_vector<word>& ws) const

   {

   // From https://briansmith.org/ecc-inversion-addition-chains-01

   BigInt r, x2, x3, x15, x30, tmp, rl;

   r = x;

   curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x, tmp, ws);

   x2 = r;

   curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x, tmp, ws);

   x3 = r;

   for(size_t i = 0; i != 3; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x3, tmp, ws);

   rl = r;

   for(size_t i = 0; i != 6; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, rl, tmp, ws);

   for(size_t i = 0; i != 3; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x3, tmp, ws);

   x15 = r;

   for(size_t i = 0; i != 15; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x15, tmp, ws);

   x30 = r;

   for(size_t i = 0; i != 30; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x30, tmp, ws);

   rl = r;

   for(size_t i = 0; i != 60; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, rl, tmp, ws);

   rl = r;

   for(size_t i = 0; i != 120; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, rl, tmp, ws);

   for(size_t i = 0; i != 15; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x15, tmp, ws);

   for(size_t i = 0; i != 31; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x30, tmp, ws);

   for(size_t i = 0; i != 2; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x2, tmp, ws);

   for(size_t i = 0; i != 94; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x30, tmp, ws);

   for(size_t i = 0; i != 2; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x, tmp, ws);

   return r;

   }

/**

* The NIST P-521 curve

*/

class CurveGFp_P521 final : public CurveGFp_NIST

   {

   public:

      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_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;

   };

BigInt CurveGFp_P521::invert_element(const BigInt& x, secure_vector<word>& ws) const

   {

   // Addition chain from https://eprint.iacr.org/2014/852.pdf section

   BigInt r;

   BigInt rl;

   BigInt a7;

   BigInt tmp;

   curve_sqr(r, x, ws);

   curve_mul_tmp(r, x, tmp, ws);

   curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x, tmp, ws);

   rl = r;

   for(size_t i = 0; i != 3; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, rl, tmp, ws);

   curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x, tmp, ws);

   a7 = r; // need this value later

   curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x, tmp, ws);

   rl = r;

   for(size_t i = 0; i != 8; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, rl, tmp, ws);

   rl = r;

   for(size_t i = 0; i != 16; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, rl, tmp, ws);

   rl = r;

   for(size_t i = 0; i != 32; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, rl, tmp, ws);

   rl = r;

   for(size_t i = 0; i != 64; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, rl, tmp, ws);

   rl = r;

   for(size_t i = 0; i != 128; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, rl, tmp, ws);

   rl = r;

   for(size_t i = 0; i != 256; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, rl, tmp, ws);

   for(size_t i = 0; i != 7; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, a7, tmp, ws);

   for(size_t i = 0; i != 2; ++i)

      curve_sqr_tmp(r, tmp, ws);

   curve_mul_tmp(r, x, tmp, ws);

   return r;

   }

}

std::shared_ptr<CurveGFp_Repr>

CurveGFp::choose_repr(const BigInt& p, const BigInt& a, const BigInt& b)

   {

   if(p == prime_p192())

      return std::make_shared<CurveGFp_P192>(a, b);

   if(p == prime_p224())

      return std::make_shared<CurveGFp_P224>(a, b);

   if(p == prime_p256())

      return std::make_shared<CurveGFp_P256>(a, b);

   if(p == prime_p384())

      return std::make_shared<CurveGFp_P384>(a, b);

   if(p == prime_p521())

      return std::make_shared<CurveGFp_P521>(a, b);

   return std::make_shared<CurveGFp_Montgomery>(p, a, b);

   }

}