/*

* (C) 2016 Jack Lloyd

*

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

*/

#ifndef BOTAN_STATEFUL_RNG_H_

#define BOTAN_STATEFUL_RNG_H_

#include <botan/mutex.h>

#include <botan/rng.h>

namespace Botan {

/**

* Inherited by RNGs which maintain in-process state, like HMAC_DRBG.

* On Unix these RNGs are vulnerable to problems with fork, where the

* RNG state is duplicated, and the parent and child process RNGs will

* produce identical output until one of them reseeds. Stateful_RNG

* reseeds itself whenever a fork is detected, or after a set number of

* bytes have been output.

*

* Not implemented by RNGs which access an external RNG, such as the

* system PRNG or a hardware RNG.

*/

class BOTAN_PUBLIC_API(2, 0) Stateful_RNG : public RandomNumberGenerator {

   public:

      /**

      * @param rng is a reference to some RNG which will be used

      * to perform the periodic reseeding

      * @param entropy_sources will be polled to perform reseeding periodically

      * @param reseed_interval specifies a limit of how many times

      * the RNG will be called before automatic reseeding is performed

      */

      Stateful_RNG(RandomNumberGenerator& rng, Entropy_Sources& entropy_sources, size_t reseed_interval) :

            m_underlying_rng(&rng), m_entropy_sources(&entropy_sources), m_reseed_interval(reseed_interval) {}

      /**

      * @param rng is a reference to some RNG which will be used

      * to perform the periodic reseeding

      * @param reseed_interval specifies a limit of how many times

      * the RNG will be called before automatic reseeding is performed

      */

      Stateful_RNG(RandomNumberGenerator& rng, size_t reseed_interval) :

            m_underlying_rng(&rng), m_reseed_interval(reseed_interval) {}

      /**

      * @param entropy_sources will be polled to perform reseeding periodically

      * @param reseed_interval specifies a limit of how many times

      * the RNG will be called before automatic reseeding is performed

      */

      Stateful_RNG(Entropy_Sources& entropy_sources, size_t reseed_interval) :

            m_entropy_sources(&entropy_sources), m_reseed_interval(reseed_interval) {}

      /**

      * In this case, automatic reseeding is impossible

      */

      Stateful_RNG() : m_reseed_interval(0) {}

      /**

      * Consume this input and mark the RNG as initialized regardless

      * of the length of the input or the current seeded state of

      * the RNG.

      */

      void initialize_with(std::span<const uint8_t> input);

      void initialize_with(const uint8_t input[], size_t length) { this->initialize_with(std::span(input, length)); }

      bool is_seeded() const override final;

      bool accepts_input() const override final { return true; }

      /**

      * Mark state as requiring a reseed on next use

      */

      void force_reseed();

      void reseed_from_rng(RandomNumberGenerator& rng, size_t poll_bits = BOTAN_RNG_RESEED_POLL_BITS) override final;

      /**

      * Poll provided sources for up to poll_bits bits of entropy

      * or until the timeout expires. Returns estimate of the number

      * of bits collected.

      */

      size_t reseed(Entropy_Sources& srcs,

                    size_t poll_bits = BOTAN_RNG_RESEED_POLL_BITS,

                    std::chrono::milliseconds poll_timeout = BOTAN_RNG_RESEED_DEFAULT_TIMEOUT) override;

      /**

      * @return intended security level of this DRBG

      */

      virtual size_t security_level() const = 0;

      /**

      * Some DRBGs have a notion of the maximum number of bytes per

      * request.  Longer requests (to randomize) will be treated as

      * multiple requests, and may initiate reseeding multiple times,

      * depending on the values of max_number_of_bytes_per_request and

      * reseed_interval(). This function returns zero if the RNG in

      * question does not have such a notion.

      *

      * @return max number of bytes per request (or zero)

      */

      virtual size_t max_number_of_bytes_per_request() const = 0;

      size_t reseed_interval() const { return m_reseed_interval; }

      void clear() override final;

   protected:

      void reseed_check();

      virtual void generate_output(std::span<uint8_t> output, std::span<const uint8_t> input) = 0;

      virtual void update(std::span<const uint8_t> input) = 0;

      virtual void clear_state() = 0;

   private:

      void generate_batched_output(std::span<uint8_t> output, std::span<const uint8_t> input);

      void fill_bytes_with_input(std::span<uint8_t> output, std::span<const uint8_t> input) override final;

      void reset_reseed_counter();

      mutable recursive_mutex_type m_mutex;

      // A non-owned and possibly null pointer to shared RNG

      RandomNumberGenerator* m_underlying_rng = nullptr;

      // A non-owned and possibly null pointer to a shared Entropy_Source

      Entropy_Sources* m_entropy_sources = nullptr;

      const size_t m_reseed_interval;

      uint32_t m_last_pid = 0;

      /*

      * Set to 1 after a successful seeding, then incremented.  Reset

      * to 0 by clear() or a fork. This logic is used even if

      * automatic reseeding is disabled (via m_reseed_interval = 0)

      */

      size_t m_reseed_counter = 0;

};

}  // namespace Botan

#endif