ctr.cpp

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/*
* Counter mode
* (C) 1999-2011,2014 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/internal/ctr.h>
 
#include <botan/exceptn.h>
#include <botan/internal/bit_ops.h>
#include <botan/internal/fmt.h>
#include <botan/internal/loadstor.h>
 
namespace Botan {
 
CTR_BE::CTR_BE(std::unique_ptr<BlockCipher> cipher) :
      m_cipher(std::move(cipher)),
      m_block_size(m_cipher->block_size()),
      m_ctr_size(m_block_size),
      m_ctr_blocks(m_cipher->parallel_bytes() / m_block_size),
      m_counter(m_cipher->parallel_bytes()),
      m_pad(m_counter.size()),
      m_pad_pos(0) {}
 
CTR_BE::CTR_BE(std::unique_ptr<BlockCipher> cipher, size_t ctr_size) :
      m_cipher(std::move(cipher)),
      m_block_size(m_cipher->block_size()),
      m_ctr_size(ctr_size),
      m_ctr_blocks(m_cipher->parallel_bytes() / m_block_size),
      m_counter(m_cipher->parallel_bytes()),
      m_pad(m_counter.size()),
      m_pad_pos(0) {
   BOTAN_ARG_CHECK(m_ctr_size >= 4 && m_ctr_size <= m_block_size, "Invalid CTR-BE counter size");
}
 
void CTR_BE::clear() {
   m_cipher->clear();
   zeroise(m_pad);
   zeroise(m_counter);
   zap(m_iv);
   m_pad_pos = 0;
}
 
size_t CTR_BE::default_iv_length() const {
   return m_block_size;
}
 
bool CTR_BE::valid_iv_length(size_t iv_len) const {
   return (iv_len <= m_block_size);
}
 
size_t CTR_BE::buffer_size() const {
   return m_pad.size();
}
 
Key_Length_Specification CTR_BE::key_spec() const {
   return m_cipher->key_spec();
}
 
std::unique_ptr<StreamCipher> CTR_BE::new_object() const {
   return std::make_unique<CTR_BE>(m_cipher->new_object(), m_ctr_size);
}
 
bool CTR_BE::has_keying_material() const {
   return m_cipher->has_keying_material();
}
 
void CTR_BE::key_schedule(std::span<const uint8_t> key) {
   m_cipher->set_key(key);
 
   // Set a default all-zeros IV
   set_iv(nullptr, 0);
}
 
std::string CTR_BE::name() const {
   if(m_ctr_size == m_block_size) {
      return fmt("CTR-BE({})", m_cipher->name());
   } else {
      return fmt("CTR-BE({},{})", m_cipher->name(), m_ctr_size);
   }
}
 
void CTR_BE::cipher_bytes(const uint8_t in[], uint8_t out[], size_t length) {
   assert_key_material_set();
 
   const uint8_t* pad_bits = &m_pad[0];
   const size_t pad_size = m_pad.size();
 
   if(m_pad_pos > 0) {
      const size_t avail = pad_size - m_pad_pos;
      const size_t take = std::min(length, avail);
      xor_buf(out, in, pad_bits + m_pad_pos, take);
      length -= take;
      in += take;
      out += take;
      m_pad_pos += take;
 
      if(take == avail) {
         add_counter(m_ctr_blocks);
         m_cipher->encrypt_n(m_counter.data(), m_pad.data(), m_ctr_blocks);
         m_pad_pos = 0;
      }
   }
 
   while(length >= pad_size) {
      xor_buf(out, in, pad_bits, pad_size);
      length -= pad_size;
      in += pad_size;
      out += pad_size;
 
      add_counter(m_ctr_blocks);
      m_cipher->encrypt_n(m_counter.data(), m_pad.data(), m_ctr_blocks);
   }
 
   xor_buf(out, in, pad_bits, length);
   m_pad_pos += length;
}
 
void CTR_BE::generate_keystream(uint8_t out[], size_t length) {
   assert_key_material_set();
 
   const size_t avail = m_pad.size() - m_pad_pos;
   const size_t take = std::min(length, avail);
   copy_mem(out, &m_pad[m_pad_pos], take);
   length -= take;
   out += take;
   m_pad_pos += take;
 
   while(length >= m_pad.size()) {
      add_counter(m_ctr_blocks);
      m_cipher->encrypt_n(m_counter.data(), out, m_ctr_blocks);
 
      length -= m_pad.size();
      out += m_pad.size();
   }
 
   if(m_pad_pos == m_pad.size()) {
      add_counter(m_ctr_blocks);
      m_cipher->encrypt_n(m_counter.data(), m_pad.data(), m_ctr_blocks);
      m_pad_pos = 0;
   }
 
   copy_mem(out, &m_pad[0], length);
   m_pad_pos += length;
   BOTAN_ASSERT_NOMSG(m_pad_pos < m_pad.size());
}
 
void CTR_BE::set_iv_bytes(const uint8_t iv[], size_t iv_len) {
   if(!valid_iv_length(iv_len)) {
      throw Invalid_IV_Length(name(), iv_len);
   }
 
   m_iv.resize(m_block_size);
   zeroise(m_iv);
   copy_mem(&m_iv[0], iv, iv_len);
 
   seek(0);
}
 
void CTR_BE::add_counter(const uint64_t counter) {
   const size_t ctr_size = m_ctr_size;
   const size_t ctr_blocks = m_ctr_blocks;
   const size_t BS = m_block_size;
 
   if(ctr_size == 4) {
      const size_t off = (BS - 4);
      const uint32_t low32 = static_cast<uint32_t>(counter + load_be<uint32_t>(&m_counter[off], 0));
 
      for(size_t i = 0; i != ctr_blocks; ++i) {
         store_be(uint32_t(low32 + i), &m_counter[i * BS + off]);
      }
   } else if(ctr_size == 8) {
      const size_t off = (BS - 8);
      const uint64_t low64 = counter + load_be<uint64_t>(&m_counter[off], 0);
 
      for(size_t i = 0; i != ctr_blocks; ++i) {
         store_be(uint64_t(low64 + i), &m_counter[i * BS + off]);
      }
   } else if(ctr_size == 16) {
      const size_t off = (BS - 16);
      uint64_t b0 = load_be<uint64_t>(&m_counter[off], 0);
      uint64_t b1 = load_be<uint64_t>(&m_counter[off], 1);
      b1 += counter;
      b0 += (b1 < counter) ? 1 : 0;  // carry
 
      for(size_t i = 0; i != ctr_blocks; ++i) {
         store_be(b0, &m_counter[i * BS + off]);
         store_be(b1, &m_counter[i * BS + off + 8]);
         b1 += 1;
         b0 += (b1 == 0);  // carry
      }
   } else {
      for(size_t i = 0; i != ctr_blocks; ++i) {
         uint64_t local_counter = counter;
         uint16_t carry = static_cast<uint8_t>(local_counter);
         for(size_t j = 0; (carry || local_counter) && j != ctr_size; ++j) {
            const size_t off = i * BS + (BS - 1 - j);
            const uint16_t cnt = static_cast<uint16_t>(m_counter[off]) + carry;
            m_counter[off] = static_cast<uint8_t>(cnt);
            local_counter = (local_counter >> 8);
            carry = (cnt >> 8) + static_cast<uint8_t>(local_counter);
         }
      }
   }
}
 
void CTR_BE::seek(uint64_t offset) {
   assert_key_material_set();
 
   const uint64_t base_counter = m_ctr_blocks * (offset / m_counter.size());
 
   zeroise(m_counter);
   BOTAN_ASSERT_NOMSG(m_counter.size() >= m_iv.size());
   copy_mem(&m_counter[0], &m_iv[0], m_iv.size());
 
   const size_t BS = m_block_size;
 
   // Set m_counter blocks to IV, IV + 1, ... IV + n
 
   if(m_ctr_size == 4 && BS >= 8) {
      const uint32_t low32 = load_be<uint32_t>(&m_counter[BS - 4], 0);
 
      if(m_ctr_blocks >= 4 && is_power_of_2(m_ctr_blocks)) {
         size_t written = 1;
         while(written < m_ctr_blocks) {
            copy_mem(&m_counter[written * BS], &m_counter[0], BS * written);
            written *= 2;
         }
      } else {
         for(size_t i = 1; i != m_ctr_blocks; ++i) {
            copy_mem(&m_counter[i * BS], &m_counter[0], BS - 4);
         }
      }
 
      for(size_t i = 1; i != m_ctr_blocks; ++i) {
         const uint32_t c = static_cast<uint32_t>(low32 + i);
         store_be(c, &m_counter[(BS - 4) + i * BS]);
      }
   } else {
      // do everything sequentially:
      for(size_t i = 1; i != m_ctr_blocks; ++i) {
         copy_mem(&m_counter[i * BS], &m_counter[(i - 1) * BS], BS);
 
         for(size_t j = 0; j != m_ctr_size; ++j) {
            if(++m_counter[i * BS + (BS - 1 - j)]) {
               break;
            }
         }
      }
   }
 
   if(base_counter > 0) {
      add_counter(base_counter);
   }
 
   m_cipher->encrypt_n(m_counter.data(), m_pad.data(), m_ctr_blocks);
   m_pad_pos = offset % m_counter.size();
}
}  // namespace Botan