Coverage Report

Created: 2021-02-21 07:20

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