argon2pwhash.cpp

/**
* (C) 2019 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/argon2.h>
#include <botan/exceptn.h>
#include <botan/internal/timer.h>
#include <algorithm>

namespace Botan {

Argon2::Argon2(uint8_t family, size_t M, size_t t, size_t p) :
   m_family(family),
   m_M(M),
   m_t(t),
   m_p(p)
   {}

void Argon2::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
   {
   argon2(output, output_len,
          password, password_len,
          salt, salt_len,
          nullptr, 0,
          nullptr, 0,
          m_family, m_p, m_M, m_t);
   }

namespace {

std::string argon2_family_name(uint8_t f)
   {
   switch(f)
      {
      case 0:
         return "Argon2d";
      case 1:
         return "Argon2i";
      case 2:
         return "Argon2id";
      default:
         throw Invalid_Argument("Unknown Argon2 parameter");
      }
   }

}

std::string Argon2::to_string() const
   {
   return argon2_family_name(m_family) + "(" +
      std::to_string(m_M) + "," +
      std::to_string(m_t) + "," +
      std::to_string(m_p) + ")";
  }

Argon2_Family::Argon2_Family(uint8_t family) : m_family(family)
   {
   if(m_family != 0 && m_family != 1 && m_family != 2)
      throw Invalid_Argument("Unknown Argon2 family identifier");
   }

std::string Argon2_Family::name() const
   {
   return argon2_family_name(m_family);
   }

std::unique_ptr<PasswordHash> Argon2_Family::tune(size_t /*output_length*/,
                                                  std::chrono::milliseconds msec,
                                                  size_t max_memory) const
   {
   const size_t max_kib = (max_memory == 0) ? 256*1024 : max_memory*1024;

   // Tune with a large memory otherwise we measure cache vs RAM speeds and underestimate
   // costs for larger params. Default is 36 MiB, or use 128 for long times.
   const size_t tune_M = (msec >= std::chrono::milliseconds(500) ? 128 : 36) * 1024;
   const size_t p = 1;
   size_t t = 1;

   Timer timer("Argon2");
   const auto tune_time = BOTAN_PBKDF_TUNING_TIME;

   timer.run_until_elapsed(tune_time, [&]() {
      uint8_t output[64] = { 0 };
      argon2(output, sizeof(output), "test", 4, nullptr, 0, nullptr, 0, nullptr, 0, m_family, p, tune_M, t);
      });

   if(timer.events() == 0 || timer.value() == 0)
      return default_params();

   size_t M = 4*1024;

   const uint64_t measured_time = timer.value() / (timer.events() * (tune_M / M));

   const uint64_t target_nsec = msec.count() * static_cast<uint64_t>(1000000);

   /*
   * Argon2 scaling rules:
   * k*M, k*t, k*p all increase cost by about k
   *
   * Since we don't even take advantage of p > 1, we prefer increasing
   * t or M instead.
   *
   * If possible to increase M, prefer that.
   */

   uint64_t est_nsec = measured_time;

   if(est_nsec < target_nsec && M < max_kib)
      {
      const uint64_t desired_cost_increase = (target_nsec + est_nsec - 1) / est_nsec;
      const uint64_t mem_headroom = max_kib / M;

      const uint64_t M_mult = std::min(desired_cost_increase, mem_headroom);
      M *= static_cast<size_t>(M_mult);
      est_nsec *= M_mult;
      }

   if(est_nsec < target_nsec)
      {
      const uint64_t desired_cost_increase = (target_nsec + est_nsec - 1) / est_nsec;
      t *= static_cast<size_t>(desired_cost_increase);
      }

   return this->from_params(M, t, p);
   }

std::unique_ptr<PasswordHash> Argon2_Family::default_params() const
   {
   return this->from_params(128*1024, 1, 1);
   }

std::unique_ptr<PasswordHash> Argon2_Family::from_iterations(size_t iter) const
   {
   /*
   These choices are arbitrary, but should not change in future
   releases since they will break applications expecting deterministic
   mapping from iteration count to params
   */
   const size_t M = iter;
   const size_t t = 1;
   const size_t p = 1;
   return this->from_params(M, t, p);
   }

std::unique_ptr<PasswordHash> Argon2_Family::from_params(size_t M, size_t t, size_t p) const
   {
   return std::unique_ptr<PasswordHash>(new Argon2(m_family, M, t, p));
   }

}