cascade.cpp

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/*
* Block Cipher Cascade
* (C) 2010 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/internal/cascade.h>
#include <botan/internal/fmt.h>
 
namespace Botan {
 
void Cascade_Cipher::encrypt_n(const uint8_t in[], uint8_t out[],
                               size_t blocks) const
   {
   size_t c1_blocks = blocks * (block_size() / m_cipher1->block_size());
   size_t c2_blocks = blocks * (block_size() / m_cipher2->block_size());
 
   m_cipher1->encrypt_n(in, out, c1_blocks);
   m_cipher2->encrypt_n(out, out, c2_blocks);
   }
 
void Cascade_Cipher::decrypt_n(const uint8_t in[], uint8_t out[],
                               size_t blocks) const
   {
   size_t c1_blocks = blocks * (block_size() / m_cipher1->block_size());
   size_t c2_blocks = blocks * (block_size() / m_cipher2->block_size());
 
   m_cipher2->decrypt_n(in, out, c2_blocks);
   m_cipher1->decrypt_n(out, out, c1_blocks);
   }
 
void Cascade_Cipher::key_schedule(const uint8_t key[], size_t /*length*/)
   {
   const uint8_t* key2 = key + m_cipher1->maximum_keylength();
 
   m_cipher1->set_key(key , m_cipher1->maximum_keylength());
   m_cipher2->set_key(key2, m_cipher2->maximum_keylength());
   }
 
void Cascade_Cipher::clear()
   {
   m_cipher1->clear();
   m_cipher2->clear();
   }
 
std::string Cascade_Cipher::name() const
   {
   return fmt("Cascade({},{})", m_cipher1->name(), m_cipher2->name());
   }
 
bool Cascade_Cipher::has_keying_material() const
   {
   return m_cipher1->has_keying_material() &&
      m_cipher2->has_keying_material();
   }
 
std::unique_ptr<BlockCipher> Cascade_Cipher::new_object() const
   {
   return std::make_unique<Cascade_Cipher>(m_cipher1->new_object(),
                                           m_cipher2->new_object());
   }
 
namespace {
 
size_t euclids_algorithm(size_t a, size_t b)
   {
   while(b != 0)
      {
      size_t t = b;
      b = a % b;
      a = t;
      }
 
   return a;
   }
 
size_t block_size_for_cascade(size_t bs, size_t bs2)
   {
   if(bs == bs2)
      return bs;
 
   const size_t gcd = euclids_algorithm(bs, bs2);
 
   return (bs * bs2) / gcd;
   }
 
}
 
Cascade_Cipher::Cascade_Cipher(std::unique_ptr<BlockCipher> cipher1,
                               std::unique_ptr<BlockCipher> cipher2) :
   m_cipher1(std::move(cipher1)),
   m_cipher2(std::move(cipher2)),
   m_block_size(block_size_for_cascade(m_cipher1->block_size(), m_cipher2->block_size()))
   {
   BOTAN_ASSERT(m_block_size % m_cipher1->block_size() == 0 &&
                m_block_size % m_cipher2->block_size() == 0,
                "Combined block size is a multiple of each ciphers block");
   }
 
}