sponge.h

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/*
* Base helper class for implementing sponge constructions like Keccak or Ascon
* (C) 2025 Jack Lloyd
*     2025 René Meusel
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#ifndef BOTAN_SPONGE_CONSTRUCTION_H_
#define BOTAN_SPONGE_CONSTRUCTION_H_
 
#include <botan/assert.h>
#include <botan/types.h>
#include <array>
 
namespace Botan {
 
/**
 * A generic sponge construction with a fixed state size defined in terms of
 * "words" of an unsigned integral type.
 *
 * This is meant to be used as a base class for specific sponge constructions
 * like Keccak or Ascon.
 */
template <size_t words, std::unsigned_integral word = uint64_t>
class Sponge {
   public:
      using word_t = word;
      using state_t = std::array<word, words>;
      constexpr static size_t word_bytes = sizeof(word);
      constexpr static size_t word_bits = word_bytes * 8;
 
      struct Config final {
            size_t bit_rate;        /// The number of bits that using algorithms can modify between permutations
            state_t initial_state;  /// The state of the sponge state at initialization
      };
 
   public:
      constexpr explicit Sponge(Config config) : m_S(config.initial_state), m_S_cursor(0), m_bit_rate(config.bit_rate) {
         BOTAN_ARG_CHECK(m_bit_rate % word_bits == 0 && m_bit_rate < words * word_bits, "Invalid sponge bit rate");
      }
 
      constexpr static size_t state_bytes() { return sizeof(state_t); }
 
      constexpr static size_t state_bits() { return state_bytes() * 8; }
 
      constexpr size_t bit_rate() const { return m_bit_rate; }
 
      constexpr size_t byte_rate() const { return m_bit_rate / 8; }
 
      constexpr size_t bit_capacity() const { return state_bits() - bit_rate(); }
 
      constexpr size_t byte_capacity() const { return state_bytes() - byte_rate(); }
 
      constexpr auto& state() { return m_S; }
 
      size_t cursor() const { return m_S_cursor; }
 
      size_t& _cursor() { return m_S_cursor; }
 
   protected:
      void reset_cursor() { m_S_cursor = 0; }
 
   private:
      state_t m_S;
      size_t m_S_cursor;
      size_t m_bit_rate;
};
 
}  // namespace Botan
 
#endif