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/*
* HMAC RNG
* (C) 2008,2013 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/mac.h>
#include <botan/rng.h>
#include <vector>
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 can 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 : public RandomNumberGenerator
{
public:
void randomize(byte buf[], size_t len) override;
bool is_seeded() const override;
void clear() override;
std::string name() const override;
size_t reseed_with_sources(Entropy_Sources& srcs,
size_t poll_bits,
std::chrono::milliseconds poll_timeout) override;
void add_entropy(const byte[], size_t) override;
/**
* @param extractor a MAC used for extracting the entropy
* @param prf a MAC used as a PRF using HKDF construction
*/
HMAC_RNG(MessageAuthenticationCode* extractor,
MessageAuthenticationCode* prf);
private:
std::unique_ptr<MessageAuthenticationCode> m_extractor;
std::unique_ptr<MessageAuthenticationCode> m_prf;
enum HMAC_PRF_Label {
Running,
Reseed,
ExtractorSeed,
};
void new_K_value(byte label);
size_t m_collected_entropy_estimate = 0;
size_t m_output_since_reseed = 0;
secure_vector<byte> m_K;
u32bit m_counter = 0;
};
}
#endif
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