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/*
* (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/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(const uint8_t input[], size_t length);
bool is_seeded() const override final;
/**
* 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;
/**
* Overrides default implementation and also includes the current
* process ID and the reseed counter.
*/
void randomize_with_ts_input(uint8_t output[], size_t output_len) 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;
protected:
void reseed_check();
/**
* Called by a subclass to notify that a reseed has been
* successfully performed.
*/
void reset_reseed_counter() { m_reseed_counter = 1; }
private:
// 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;
};
}
#endif
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