cmac.cpp

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/*
* CMAC
* (C) 1999-2007,2014 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/internal/cmac.h>
 
#include <botan/exceptn.h>
#include <botan/mem_ops.h>
#include <botan/internal/buffer_slicer.h>
#include <botan/internal/fmt.h>
#include <botan/internal/poly_dbl.h>
 
namespace Botan {
 
/*
* Update an CMAC Calculation
*/
void CMAC::add_data(std::span<const uint8_t> input) {
   assert_key_material_set();
 
   const size_t bs = output_length();
 
   const size_t initial_fill = std::min(m_buffer.size() - m_position, input.size());
   copy_mem(m_buffer.data() + m_position, input.data(), initial_fill);
 
   if(m_position + input.size() > bs) {
      xor_buf(m_state, m_buffer, bs);
      m_cipher->encrypt(m_state);
 
      BufferSlicer in(input);
      in.skip(bs - m_position);
      while(in.remaining() > bs) {
         xor_buf(m_state, in.take(bs), bs);
         m_cipher->encrypt(m_state);
      }
 
      const auto remaining = in.take(in.remaining());
      copy_mem(m_buffer.data(), remaining.data(), remaining.size());
      m_position = remaining.size();
   } else {
      m_position += input.size();
   }
}
 
/*
* Finalize an CMAC Calculation
*/
void CMAC::final_result(std::span<uint8_t> mac) {
   xor_buf(m_state, m_buffer, m_position);
 
   if(m_position == output_length()) {
      xor_buf(m_state, m_B, output_length());
   } else {
      m_state[m_position] ^= 0x80;
      xor_buf(m_state, m_P, output_length());
   }
 
   m_cipher->encrypt(m_state);
 
   copy_mem(mac.data(), m_state.data(), output_length());
 
   zeroise(m_state);
   zeroise(m_buffer);
   m_position = 0;
}
 
void CMAC::start_msg(std::span<const uint8_t> nonce) {
   if(!nonce.empty()) {
      throw Invalid_IV_Length(name(), nonce.size());
   }
   assert_key_material_set();
 
   zeroise(m_state);
   zeroise(m_buffer);
   m_position = 0;
}
 
bool CMAC::has_keying_material() const {
   return m_cipher->has_keying_material();
}
 
/*
* CMAC Key Schedule
*/
void CMAC::key_schedule(std::span<const uint8_t> key) {
   clear();
   m_cipher->set_key(key);
   m_cipher->encrypt(m_B);
   poly_double_n(m_B.data(), m_B.size());
   poly_double_n(m_P.data(), m_B.data(), m_P.size());
}
 
/*
* Clear memory of sensitive data
*/
void CMAC::clear() {
   m_cipher->clear();
   zeroise(m_state);
   zeroise(m_buffer);
   zeroise(m_B);
   zeroise(m_P);
   m_position = 0;
}
 
/*
* Return the name of this type
*/
std::string CMAC::name() const {
   return fmt("CMAC({})", m_cipher->name());
}
 
/*
* Return a new_object of this object
*/
std::unique_ptr<MessageAuthenticationCode> CMAC::new_object() const {
   return std::make_unique<CMAC>(m_cipher->new_object());
}
 
/*
* CMAC Constructor
*/
CMAC::CMAC(std::unique_ptr<BlockCipher> cipher) : m_cipher(std::move(cipher)), m_block_size(m_cipher->block_size()) {
   if(!poly_double_supported_size(m_block_size)) {
      throw Invalid_Argument(fmt("CMAC cannot use the {} bit cipher {}", m_block_size * 8, m_cipher->name()));
   }
 
   m_state.resize(output_length());
   m_buffer.resize(output_length());
   m_B.resize(output_length());
   m_P.resize(output_length());
   m_position = 0;
}
 
}  // namespace Botan