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/*
* HMAC RNG
* (C) 2008,2013,2016 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#ifndef BOTAN_HMAC_RNG_H__
#define BOTAN_HMAC_RNG_H__
#include <botan/stateful_rng.h>
#include <botan/mac.h>
namespace Botan {
/**
* HMAC_RNG - based on the design described in "On Extract-then-Expand
* Key Derivation Functions and an HMAC-based KDF" by Hugo Krawczyk
* (henceforce, 'E-t-E')
*
* However it actually could be parameterized with any two MAC functions,
* not restricted to HMAC (this variation is also described in
* Krawczyk's paper), for instance one could use HMAC(SHA-512) as the
* extractor and CMAC(AES-256) as the PRF.
*/
class BOTAN_DLL HMAC_RNG final : public Stateful_RNG
{
public:
/**
* Initialize an HMAC_RNG instance with the given MAC as PRF (normally HMAC)
* @param underlying_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.
*/
HMAC_RNG(std::unique_ptr<MessageAuthenticationCode> prf,
RandomNumberGenerator& underlying_rng,
Entropy_Sources& entropy_sources,
size_t reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL);
/**
* Initialize an HMAC_RNG instance with the given MAC as PRF (normally HMAC)
* @param underlying_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.
*/
HMAC_RNG(std::unique_ptr<MessageAuthenticationCode> prf,
RandomNumberGenerator& underlying_rng,
size_t reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL);
/*
* Initialize an HMAC_RNG instance with the given MAC as PRF (normally HMAC)
* @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.
*/
HMAC_RNG(std::unique_ptr<MessageAuthenticationCode> prf,
Entropy_Sources& entropy_sources,
size_t reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL);
/**
* Initialize an HMAC_RNG instance with the given MAC as PRF (normally HMAC)
* Automatic reseeding is disabled completely.
*/
HMAC_RNG(std::unique_ptr<MessageAuthenticationCode> prf);
void randomize(byte buf[], size_t len) override;
void clear() override;
std::string name() const override;
size_t reseed(Entropy_Sources& srcs,
size_t poll_bits,
std::chrono::milliseconds poll_timeout) override;
void add_entropy(const byte[], size_t) override;
size_t security_level() const override { return m_prf->output_length() * 8 / 2; }
private:
std::unique_ptr<MessageAuthenticationCode> m_prf;
std::unique_ptr<MessageAuthenticationCode> m_extractor;
enum HMAC_PRF_Label {
Running,
BlockFinished,
Reseed,
ExtractorSeed,
};
void new_K_value(byte label);
secure_vector<byte> m_K;
u32bit m_counter = 0;
};
}
#endif
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