entropy_srcs.cpp

Go to the documentation of this file.

/*
* 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