chacha.h

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/*
* ChaCha20
* (C) 2014,2018 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#ifndef BOTAN_CHACHA_H_
#define BOTAN_CHACHA_H_
 
#include <botan/stream_cipher.h>
 
namespace Botan {
 
/**
* DJB's ChaCha (https://cr.yp.to/chacha.html)
*/
class ChaCha final : public StreamCipher {
   public:
      /**
      * @param rounds number of rounds
      * @note Currently only 8, 12 or 20 rounds are supported, all others
      * will throw an exception
      */
      explicit ChaCha(size_t rounds = 20);
 
      std::string provider() const override;
 
      /*
      * ChaCha accepts 0, 8, 12 or 24 byte IVs.
      * The default IV is a 8 zero bytes.
      * An IV of length 0 is treated the same as the default zero IV.
      * An IV of length 24 selects XChaCha mode
      */
      bool valid_iv_length(size_t iv_len) const override;
 
      size_t default_iv_length() const override;
 
      Key_Length_Specification key_spec() const override;
 
      void clear() override;
 
      std::unique_ptr<StreamCipher> new_object() const override;
 
      std::string name() const override;
 
      void seek(uint64_t offset) override;
 
      bool supports_seek() const override { return true; }
 
      std::optional<uint64_t> remaining_keystream_bytes() const override;
 
      bool has_keying_material() const override;
 
      size_t buffer_size() const override;
 
   private:
      void key_schedule(std::span<const uint8_t> key) override;
 
      void cipher_bytes(const uint8_t in[], uint8_t out[], size_t length) override;
 
      void generate_keystream(uint8_t out[], size_t len) override;
 
      void set_iv_bytes(const uint8_t iv[], size_t iv_len) override;
 
      void initialize_state();
 
      static size_t parallelism();
 
      static void chacha(uint8_t output[], size_t output_blocks, uint32_t state[16], size_t rounds);
 
#if defined(BOTAN_HAS_CHACHA_SIMD32)
      static void chacha_simd32_x4(uint8_t output[64 * 4], uint32_t state[16], size_t rounds);
#endif
 
#if defined(BOTAN_HAS_CHACHA_AVX2)
      static void chacha_avx2_x8(uint8_t output[64 * 8], uint32_t state[16], size_t rounds);
#endif
 
#if defined(BOTAN_HAS_CHACHA_AVX512)
      static void chacha_avx512_x16(uint8_t output[64 * 16], uint32_t state[16], size_t rounds);
#endif
 
      size_t m_rounds;
      secure_vector<uint32_t> m_key;
      secure_vector<uint32_t> m_state;
      secure_vector<uint8_t> m_buffer;
      size_t m_position = 0;
      size_t m_iv_length = 0;
      uint32_t m_state13_post_iv = 0;
      // Valid only when m_iv_length == 12: bytes the user can still
      // generate before the 32-bit counter would wrap into the nonce.
      uint64_t m_bytes_remaining = 0;
};
 
}  // namespace Botan
 
#endif