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/*
* ChaCha_RNG
* (C) 2017 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#ifndef BOTAN_CHACHA_RNG_H_
#define BOTAN_CHACHA_RNG_H_
#include <botan/stateful_rng.h>
#include <botan/stream_cipher.h>
#include <botan/mac.h>
namespace Botan {
class Entropy_Sources;
/**
* ChaCha_RNG is a very fast but completely ad-hoc RNG created by
* creating a 256-bit random value and using it as a key for ChaCha20.
*
* The RNG maintains two 256-bit keys, one for HMAC_SHA256 (HK) and the
* other for ChaCha20 (CK). To compute a new key in response to
* reseeding request or add_entropy calls, ChaCha_RNG computes
* CK' = HMAC_SHA256(HK, input_material)
* Then a new HK' is computed by running ChaCha20 with the new key to
* output 32 bytes:
* HK' = ChaCha20(CK')
*
* Now output can be produced by continuing to produce output with ChaCha20
* under CK'
*
* The first HK (before seeding occurs) is taken as the all zero value.
*
* @warning This RNG construction is probably fine but is non-standard.
* The primary reason to use it is in cases where the other RNGs are
* not fast enough.
*/
class BOTAN_PUBLIC_API(2,3) ChaCha_RNG final : public Stateful_RNG
{
public:
/**
* Automatic reseeding is disabled completely, as it has no access to
* any source for seed material.
*
* If a fork is detected, the RNG will be unable to reseed itself
* in response. In this case, an exception will be thrown rather
* than generating duplicated output.
*/
ChaCha_RNG();
/**
* Provide an initial seed to the RNG, without providing an
* underlying RNG or entropy source. Automatic reseeding is
* disabled completely, as it has no access to any source for
* seed material.
*
* If a fork is detected, the RNG will be unable to reseed itself
* in response. In this case, an exception will be thrown rather
* than generating duplicated output.
*
* @param seed the seed material, should be at least 256 bits
*/
ChaCha_RNG(const secure_vector<uint8_t>& seed);
/**
* Automatic reseeding from @p underlying_rng will take place after
* @p reseed_interval many requests or after a fork was detected.
*
* @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
*/
ChaCha_RNG(RandomNumberGenerator& underlying_rng,
size_t reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL);
/**
* Automatic reseeding from @p entropy_sources will take place after
* @p reseed_interval many requests or after a fork was detected.
*
* @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.
*/
ChaCha_RNG(Entropy_Sources& entropy_sources,
size_t reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL);
/**
* Automatic reseeding from @p underlying_rng and @p entropy_sources
* will take place after @p reseed_interval many requests or after
* a fork was detected.
*
* @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.
*/
ChaCha_RNG(RandomNumberGenerator& underlying_rng,
Entropy_Sources& entropy_sources,
size_t reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL);
std::string name() const override { return "ChaCha_RNG"; }
size_t security_level() const override;
size_t max_number_of_bytes_per_request() const override { return 0; }
private:
void update(const uint8_t input[], size_t input_len) override;
void generate_output(uint8_t output[], size_t output_len,
const uint8_t input[], size_t input_len) override;
void clear_state() override;
std::unique_ptr<MessageAuthenticationCode> m_hmac;
std::unique_ptr<StreamCipher> m_chacha;
};
}
#endif
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