ecc_helper.h - mozsearch

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/*

* (C) 2015,2016 Jack Lloyd

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

*/

#ifndef ECC_HELPERS_H_

#define ECC_HELPERS_H_

#include "fuzzers.h"

#include <botan/ec_group.h>

#include <botan/reducer.h>

#include <botan/numthry.h>

namespace {

inline std::ostream& operator<<(std::ostream& o, const Botan::PointGFp& point)

   o << point.get_affine_x() << "," << point.get_affine_y();

   return o;

Botan::BigInt decompress_point(bool yMod2,

                               const Botan::BigInt& x,

                               const Botan::BigInt& curve_p,

                               const Botan::BigInt& curve_a,

                               const Botan::BigInt& curve_b)

   Botan::BigInt xpow3 = x * x * x;

   Botan::BigInt g = curve_a * x;

   g += xpow3;

   g += curve_b;

   g = g % curve_p;

   Botan::BigInt z = ressol(g, curve_p);

   if(z < 0)

      throw Botan::Exception("Could not perform square root");

   if(z.get_bit(0) != yMod2)

      z = curve_p - z;

   return z;

void check_ecc_math(const Botan::EC_Group& group,

                    const uint8_t in[], size_t len)

   // These depend only on the group, which is also static

   static const Botan::PointGFp base_point = group.get_base_point();

   // This is shared across runs to reduce overhead

   static std::vector<Botan::BigInt> ws(Botan::PointGFp::WORKSPACE_SIZE);

   const size_t hlen = len / 2;

   const Botan::BigInt a = Botan::BigInt::decode(in, hlen);

   const Botan::BigInt b = Botan::BigInt::decode(in + hlen, len - hlen);

   const Botan::BigInt c = a + b;

   const Botan::PointGFp P1 = base_point * a;

   const Botan::PointGFp Q1 = base_point * b;

   const Botan::PointGFp R1 = base_point * c;

   const Botan::PointGFp S1 = P1 + Q1;

   const Botan::PointGFp T1 = Q1 + P1;

   FUZZER_ASSERT_EQUAL(S1, R1);

   FUZZER_ASSERT_EQUAL(T1, R1);

   const Botan::PointGFp P2 = group.blinded_base_point_multiply(a, fuzzer_rng(), ws);

   const Botan::PointGFp Q2 = group.blinded_base_point_multiply(b, fuzzer_rng(), ws);

   const Botan::PointGFp R2 = group.blinded_base_point_multiply(c, fuzzer_rng(), ws);

   const Botan::PointGFp S2 = P2 + Q2;

   const Botan::PointGFp T2 = Q2 + P2;

   FUZZER_ASSERT_EQUAL(S2, R2);

   FUZZER_ASSERT_EQUAL(T2, R2);

   const Botan::PointGFp P3 = group.blinded_var_point_multiply(base_point, a, fuzzer_rng(), ws);

   const Botan::PointGFp Q3 = group.blinded_var_point_multiply(base_point, b, fuzzer_rng(), ws);

   const Botan::PointGFp R3 = group.blinded_var_point_multiply(base_point, c, fuzzer_rng(), ws);

   const Botan::PointGFp S3 = P3 + Q3;

   const Botan::PointGFp T3 = Q3 + P3;

   FUZZER_ASSERT_EQUAL(S3, R3);

   FUZZER_ASSERT_EQUAL(T3, R3);

   FUZZER_ASSERT_EQUAL(S1, S2);

   FUZZER_ASSERT_EQUAL(S1, S3);

try

      const auto yp = decompress_point(true, a, group.get_p(), group.get_a(), group.get_b());

      const auto pt_p = group.blinded_var_point_multiply(group.point(a, yp), b, fuzzer_rng(), ws);

      const auto yn = -yp;

      const auto pt_n = group.blinded_var_point_multiply(group.point(a, yn), b, fuzzer_rng(), ws);

      FUZZER_ASSERT_EQUAL(pt_p, -pt_n);

   catch(...) {}

#endif