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/*
* HMAC RNG
* (C) 2008 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#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);
bool is_seeded() const { return seeded; }
void clear();
std::string name() const;
void reseed(size_t poll_bits);
void add_entropy_source(EntropySource* es);
void add_entropy(const byte[], size_t);
/**
* @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);
~HMAC_RNG();
private:
MessageAuthenticationCode* extractor;
MessageAuthenticationCode* prf;
std::vector<EntropySource*> entropy_sources;
bool seeded;
SecureVector<byte> K, io_buffer;
size_t user_input_len;
u32bit counter;
};
}
#endif
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