/*

* Entropy Source Polling

* (C) 2008-2010,2015 Jack Lloyd

*

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

*/

#include <botan/entropy_src.h>

#include <botan/rng.h>

#if defined(BOTAN_HAS_SYSTEM_RNG)

   #include <botan/system_rng.h>

#endif

#if defined(BOTAN_HAS_PROCESSOR_RNG)

   #include <botan/processor_rng.h>

#endif

#if defined(BOTAN_HAS_ENTROPY_SRC_RDSEED)

   #include <botan/internal/rdseed.h>

#endif

#if defined(BOTAN_HAS_ENTROPY_SRC_WIN32)

   #include <botan/internal/es_win32.h>

#endif

#if defined(BOTAN_HAS_ENTROPY_SRC_GETENTROPY)

   #include <botan/internal/getentropy.h>

#endif

namespace Botan {

namespace {

#if defined(BOTAN_HAS_SYSTEM_RNG)

class System_RNG_EntropySource final : public Entropy_Source {

   public:

      size_t poll(RandomNumberGenerator& rng) override {

         const size_t poll_bits = BOTAN_RNG_RESEED_POLL_BITS;

         rng.reseed_from_rng(system_rng(), poll_bits);

         return poll_bits;

      }

      std::string name() const override { return "system_rng"; }

};

#endif

#if defined(BOTAN_HAS_PROCESSOR_RNG)

class Processor_RNG_EntropySource final : public Entropy_Source {

   public:

      size_t poll(RandomNumberGenerator& rng) override {

         /*

         * Intel's documentation for RDRAND at

         * https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide

         * claims that software can guarantee a reseed event by polling enough data:

         * "There is an upper bound of 511 samples per seed in the implementation

         * where samples are 128 bits in size and can provide two 64-bit random

         * numbers each."

         *

         * By requesting 65536 bits we are asking for 512 samples and thus are assured

         * that at some point in producing the output, at least one reseed of the

         * internal state will occur.

         *

         * The reseeding conditions of the POWER and ARM processor RNGs are not known

         * but probably work in a somewhat similar manner. The exact amount requested

         * may be tweaked if and when such conditions become publically known.

         */

         const size_t poll_bits = 65536;

         rng.reseed_from_rng(m_hwrng, poll_bits);

         // Avoid trusting a black box, don't count this as contributing entropy:

         return 0;

      }

      std::string name() const override { return m_hwrng.name(); }

   private:

      Processor_RNG m_hwrng;

};

#endif

}  // namespace

std::unique_ptr<Entropy_Source> Entropy_Source::create(std::string_view name) {

#if defined(BOTAN_HAS_SYSTEM_RNG)

   if(name == "system_rng") {

      return std::make_unique<System_RNG_EntropySource>();

   }

#endif

#if defined(BOTAN_HAS_PROCESSOR_RNG)

   if(name == "hwrng") {

      if(Processor_RNG::available()) {

         return std::make_unique<Processor_RNG_EntropySource>();

      }

   }

#endif

#if defined(BOTAN_HAS_ENTROPY_SRC_RDSEED)

   if(name == "rdseed") {

      return std::make_unique<Intel_Rdseed>();

   }

#endif

#if defined(BOTAN_HAS_ENTROPY_SRC_GETENTROPY)

   if(name == "getentropy") {

      return std::make_unique<Getentropy>();

   }

#endif

#if defined(BOTAN_HAS_ENTROPY_SRC_WIN32)

   if(name == "system_stats") {

      return std::make_unique<Win32_EntropySource>();

   }

#endif

   BOTAN_UNUSED(name);

   return nullptr;

}

void Entropy_Sources::add_source(std::unique_ptr<Entropy_Source> src) {

   if(src) {

      m_srcs.push_back(std::move(src));

   }

}

std::vector<std::string> Entropy_Sources::enabled_sources() const {

   std::vector<std::string> sources;

   sources.reserve(m_srcs.size());

   for(const auto& src : m_srcs) {

      sources.push_back(src->name());

   }

   return sources;

}

size_t Entropy_Sources::poll(RandomNumberGenerator& rng, size_t poll_bits, std::chrono::milliseconds timeout) {

   typedef std::chrono::system_clock clock;

   auto deadline = clock::now() + timeout;

   size_t bits_collected = 0;

   for(auto& src : m_srcs) {

      bits_collected += src->poll(rng);

      if(bits_collected >= poll_bits || clock::now() > deadline) {

         break;

      }

   }

   return bits_collected;

}

size_t Entropy_Sources::poll_just(RandomNumberGenerator& rng, std::string_view the_src) {

   for(auto& src : m_srcs) {

      if(src->name() == the_src) {

         return src->poll(rng);

      }

   }

   return 0;

}

Entropy_Sources::Entropy_Sources(const std::vector<std::string>& sources) {

   for(auto&& src_name : sources) {

      add_source(Entropy_Source::create(src_name));

   }

}

Entropy_Sources& Entropy_Sources::global_sources() {

   static Entropy_Sources global_entropy_sources(BOTAN_ENTROPY_DEFAULT_SOURCES);

   return global_entropy_sources;

}

}  // namespace Botan