text: /**
  * (C) 2018 Jack Lloyd
  * (C) 2018 Ribose Inc
  *
  * Botan is released under the Simplified BSD License (see license.txt)
  */
  
  #include <botan/scrypt.h>
  #include <botan/pbkdf2.h>
  #include <botan/salsa20.h>
  #include <botan/loadstor.h>
  #include <botan/exceptn.h>
  #include <botan/internal/bit_ops.h>
  #include <botan/internal/timer.h>
  #include <sstream>
  
  namespace Botan {
  
  std::string Scrypt_Family::name() const
     {
     return "Scrypt";
     }
  
  std::unique_ptr<PasswordHash> Scrypt_Family::default_params() const
     {
     return std::unique_ptr<PasswordHash>(new Scrypt(32768, 8, 1));
     }
  
  std::unique_ptr<PasswordHash> Scrypt_Family::tune(size_t output_length,
                                                    std::chrono::milliseconds msec,
                                                    size_t max_memory_usage_mb) const
     {
     BOTAN_UNUSED(output_length);
  
     /*
     * Some rough relations between scrypt parameters and runtime.
     * Denote here by stime(N,r,p) the msec it takes to run scrypt.
     *
     * Emperically for smaller sizes:
     * stime(N,8*r,p) / stime(N,r,p) is ~ 6-7
     * stime(N,r,8*p) / stime(N,r,8*p) is ~ 7
     * stime(2*N,r,p) / stime(N,r,p) is ~ 2
     *
     * Compute stime(8192,1,1) as baseline and extrapolate
     */
  
     const size_t max_memory_usage = max_memory_usage_mb * 1024 * 1024;
     // Starting parameters
     size_t N = 8192;
     size_t r = 1;
     size_t p = 1;
  
     Timer timer("Scrypt");
     const auto tune_time = BOTAN_PBKDF_TUNING_TIME;
  
     timer.run_until_elapsed(tune_time, [&]() {
        uint8_t output[32] = { 0 };
        scrypt(output, sizeof(output), "test", 4, nullptr, 0, N, r, p);
        });
  
     // No timer events seems strange, perhaps something is wrong - give
     // up on this and just return default params
     if(timer.events() == 0)
        return default_params();
  
     // nsec per eval of scrypt with initial params
     const uint64_t measured_time = timer.value() / timer.events();
  
     const uint64_t target_nsec = msec.count() * static_cast<uint64_t>(1000000);
  
     uint64_t est_nsec = measured_time;
  
     // First move increase r by 8x if possible
  
     if(max_memory_usage == 0 || scrypt_memory_usage(N, r, p)*8 < max_memory_usage)
        {
        if(target_nsec / est_nsec >= 5)
           {
           r *= 8;
           est_nsec *= 5;
           }
        }
  
     // Now double N as many times as we can
  
     while(max_memory_usage == 0 || scrypt_memory_usage(N, r, p)*2 < max_memory_usage)
        {
        if(target_nsec / est_nsec >= 2)
           {
           N *= 2;
           est_nsec *= 2;
           }
        else
           break;
        }
  
     // If we have extra runtime budget, increment p
  
     if(target_nsec / est_nsec > 2)
        p *= std::min<uint64_t>(1024, (target_nsec / est_nsec));
  
     return std::unique_ptr<PasswordHash>(new Scrypt(N, r, p));
     }
  
  std::unique_ptr<PasswordHash> Scrypt_Family::from_params(size_t N, size_t r, size_t p) const
     {
     return std::unique_ptr<PasswordHash>(new Scrypt(N, r, p));
     }
  
  std::unique_ptr<PasswordHash> Scrypt_Family::from_iterations(size_t iter) const
     {
     const size_t r = 8;
     const size_t p = 1;
  
     size_t N = 8192;
  
     if(iter > 50000)
        N = 16384;
     if(iter > 100000)
        N = 32768;
     if(iter > 150000)
        N = 65536;
  
     return std::unique_ptr<PasswordHash>(new Scrypt(N, r, p));
     }
  
  Scrypt::Scrypt(size_t N, size_t r, size_t p) :
     m_N(N), m_r(r), m_p(p)
     {
     if(!is_power_of_2(N))
        throw Invalid_Argument("Scrypt N parameter must be a power of 2");
  
     if(p == 0 || p > 1024)
        throw Invalid_Argument("Invalid or unsupported scrypt p");
     if(r == 0 || r > 256)
        throw Invalid_Argument("Invalid or unsupported scrypt r");
     if(N < 1 || N > 4194304)
        throw Invalid_Argument("Invalid or unsupported scrypt N");
     }
  
  std::string Scrypt::to_string() const
     {
     std::ostringstream oss;
     oss << "Scrypt(" << m_N << "," << m_r << "," << m_p << ")";
     return oss.str();
     }
  
  size_t Scrypt::total_memory_usage() const
     {
     return scrypt_memory_usage(m_N, m_r, m_p);
     }
  
  void Scrypt::derive_key(uint8_t output[], size_t output_len,
                          const char* password, size_t password_len,
                          const uint8_t salt[], size_t salt_len) const
     {
     scrypt(output, output_len,
            password, password_len,
            salt, salt_len,
            N(), r(), p());
     }
  
  namespace {
  
  void scryptBlockMix(size_t r, uint8_t* B, uint8_t* Y)
     {
     uint32_t B32[16];
     secure_vector<uint8_t> X(64);
     copy_mem(X.data(), &B[(2*r-1)*64], 64);
  
     for(size_t i = 0; i != 2*r; i++)
        {
        xor_buf(X.data(), &B[64*i], 64);
        load_le<uint32_t>(B32, X.data(), 16);
        Salsa20::salsa_core(X.data(), B32, 8);
        copy_mem(&Y[64*i], X.data(), 64);
        }
  
     for(size_t i = 0; i < r; ++i)
        {
        copy_mem(&B[i*64], &Y[(i * 2) * 64], 64);
        }
  
     for(size_t i = 0; i < r; ++i)
        {
        copy_mem(&B[(i + r) * 64], &Y[(i * 2 + 1) * 64], 64);
        }
     }
  
  void scryptROMmix(size_t r, size_t N, uint8_t* B, secure_vector<uint8_t>& V)
     {
     const size_t S = 128 * r;
  
     for(size_t i = 0; i != N; ++i)
        {
        copy_mem(&V[S*i], B, S);
        scryptBlockMix(r, B, &V[N*S]);
        }
  
     for(size_t i = 0; i != N; ++i)
        {
        // compiler doesn't know here that N is power of 2
        const size_t j = load_le<uint32_t>(&B[(2*r-1)*64], 0) & (N - 1);
        xor_buf(B, &V[j*S], S);
        scryptBlockMix(r, B, &V[N*S]);
        }
     }
  
  }
  
  void scrypt(uint8_t output[], size_t output_len,
              const char* password, size_t password_len,
              const uint8_t salt[], size_t salt_len,
              size_t N, size_t r, size_t p)
     {
     const size_t S = 128 * r;
     secure_vector<uint8_t> B(p * S);
     // temp space
     secure_vector<uint8_t> V((N+1) * S);
  
     auto hmac_sha256 = MessageAuthenticationCode::create_or_throw("HMAC(SHA-256)");
  
     try
        {
        hmac_sha256->set_key(cast_char_ptr_to_uint8(password), password_len);
        }
     catch(Invalid_Key_Length&)
        {
        throw Invalid_Argument("Scrypt cannot accept passphrases of the provided length");
        }
  
     pbkdf2(*hmac_sha256.get(),
            B.data(), B.size(),
            salt, salt_len,
            1);
  
     // these can be parallel
     for(size_t i = 0; i != p; ++i)
        {
        scryptROMmix(r, N, &B[128*r*i], V);
        }
  
     pbkdf2(*hmac_sha256.get(),
            output, output_len,
            B.data(), B.size(),
            1);
     }
  
  }
  