path: root/src/tls/tls_record.cpp

/*
* TLS Record Handling
* (C) 2012 Jack Lloyd
*
* Released under the terms of the Botan license
*/

#include <botan/internal/tls_record.h>
#include <botan/tls_ciphersuite.h>
#include <botan/tls_exceptn.h>
#include <botan/libstate.h>
#include <botan/loadstor.h>
#include <botan/internal/tls_seq_numbers.h>
#include <botan/internal/tls_session_key.h>
#include <botan/internal/rounding.h>
#include <botan/internal/xor_buf.h>

namespace Botan {

namespace TLS {

Connection_Cipher_State::Connection_Cipher_State(Protocol_Version version,
                                                 Connection_Side side,
                                                 bool our_side,
                                                 const Ciphersuite& suite,
                                                 const Session_Keys& keys) :
   m_start_time(std::chrono::system_clock::now()),
   m_is_ssl3(version == Protocol_Version::SSL_V3)
   {
   SymmetricKey mac_key, cipher_key;
   InitializationVector iv;

   if(side == CLIENT)
      {
      cipher_key = keys.client_cipher_key();
      iv = keys.client_iv();
      mac_key = keys.client_mac_key();
      }
   else
      {
      cipher_key = keys.server_cipher_key();
      iv = keys.server_iv();
      mac_key = keys.server_mac_key();
      }

   const std::string cipher_algo = suite.cipher_algo();
   const std::string mac_algo = suite.mac_algo();

   Algorithm_Factory& af = global_state().algorithm_factory();

   if(const BlockCipher* bc = af.prototype_block_cipher(cipher_algo))
      {
      m_block_cipher.reset(bc->clone());
      m_block_cipher->set_key(cipher_key);
      m_block_cipher_cbc_state = iv.bits_of();
      m_block_size = bc->block_size();

      if(version.supports_explicit_cbc_ivs())
         m_iv_size = m_block_size;
      else
         m_iv_size = 0;
      }
   else if(const StreamCipher* sc = af.prototype_stream_cipher(cipher_algo))
      {
      m_stream_cipher.reset(sc->clone());
      m_stream_cipher->set_key(cipher_key);
      m_block_size = 0;
      m_iv_size = 0;
      }
   else
      throw Invalid_Argument("Unknown TLS cipher " + cipher_algo);

   if(version == Protocol_Version::SSL_V3)
      m_mac.reset(af.make_mac("SSL3-MAC(" + mac_algo + ")"));
   else
      m_mac.reset(af.make_mac("HMAC(" + mac_algo + ")"));

   m_mac->set_key(mac_key);
   }

void write_record(secure_vector<byte>& output,
                  byte msg_type, const byte msg[], size_t msg_length,
                  Protocol_Version version,
                  u64bit msg_sequence,
                  Connection_Cipher_State* cipherstate,
                  RandomNumberGenerator& rng)
   {
   output.clear();

   output.push_back(msg_type);
   output.push_back(version.major_version());
   output.push_back(version.minor_version());

   if(version.is_datagram_protocol())
      {
      for(size_t i = 0; i != 8; ++i)
         output.push_back(get_byte(i, msg_sequence));
      }

   if(!cipherstate) // initial unencrypted handshake records
      {
      output.push_back(get_byte<u16bit>(0, msg_length));
      output.push_back(get_byte<u16bit>(1, msg_length));

      output.insert(output.end(), &msg[0], &msg[msg_length]);

      return;
      }

   cipherstate->mac()->update_be(msg_sequence);
   cipherstate->mac()->update(msg_type);

   if(cipherstate->mac_includes_record_version())
      {
      cipherstate->mac()->update(version.major_version());
      cipherstate->mac()->update(version.minor_version());
      }

   cipherstate->mac()->update(get_byte<u16bit>(0, msg_length));
   cipherstate->mac()->update(get_byte<u16bit>(1, msg_length));
   cipherstate->mac()->update(msg, msg_length);

   const size_t block_size = cipherstate->block_size();
   const size_t iv_size = cipherstate->iv_size();
   const size_t mac_size = cipherstate->mac_size();

   const size_t buf_size = round_up(
      iv_size + msg_length + mac_size + (block_size ? 1 : 0),
      block_size);

   if(buf_size > MAX_CIPHERTEXT_SIZE)
      throw Internal_Error("Output record is larger than allowed by protocol");

   output.push_back(get_byte<u16bit>(0, buf_size));
   output.push_back(get_byte<u16bit>(1, buf_size));

   const size_t header_size = output.size();

   if(iv_size)
      {
      output.resize(output.size() + iv_size);
      rng.randomize(&output[output.size() - iv_size], iv_size);
      }

   output.insert(output.end(), &msg[0], &msg[msg_length]);

   output.resize(output.size() + mac_size);
   cipherstate->mac()->final(&output[output.size() - mac_size]);

   if(block_size)
      {
      const size_t pad_val =
         buf_size - (iv_size + msg_length + mac_size + 1);

      for(size_t i = 0; i != pad_val + 1; ++i)
         output.push_back(pad_val);
      }

   if(buf_size > MAX_CIPHERTEXT_SIZE)
      throw Internal_Error("Produced ciphertext larger than protocol allows");

   BOTAN_ASSERT(buf_size + header_size == output.size(),
                "Output buffer is sized properly");

   if(StreamCipher* sc = cipherstate->stream_cipher())
      {
      sc->cipher1(&output[header_size], buf_size);
      }
   else if(BlockCipher* bc = cipherstate->block_cipher())
      {
      secure_vector<byte>& cbc_state = cipherstate->cbc_state();

      BOTAN_ASSERT(buf_size % block_size == 0,
                   "Buffer is an even multiple of block size");

      byte* buf = &output[header_size];

      const size_t blocks = buf_size / block_size;

      xor_buf(&buf[0], &cbc_state[0], block_size);
      bc->encrypt(&buf[0]);

      for(size_t i = 1; i < blocks; ++i)
         {
         xor_buf(&buf[block_size*i], &buf[block_size*(i-1)], block_size);
         bc->encrypt(&buf[block_size*i]);
         }

      cbc_state.assign(&buf[block_size*(blocks-1)],
                       &buf[block_size*blocks]);
      }
   else
      throw Internal_Error("NULL cipher not supported");
   }

namespace {

size_t fill_buffer_to(secure_vector<byte>& readbuf,
                      const byte*& input,
                      size_t& input_size,
                      size_t& input_consumed,
                      size_t desired)
   {
   if(readbuf.size() >= desired)
      return 0; // already have it

   const size_t taken = std::min(input_size, desired - readbuf.size());

   readbuf.insert(readbuf.end(), &input[0], &input[taken]);
   input_consumed += taken;
   input_size -= taken;
   input += taken;

   return (desired - readbuf.size()); // how many bytes do we still need?
   }

/*
* MAC scheme used in SSLv3/TLSv1 for RC4 and CBC ciphers
*/
bool traditional_mac_check(Record& output_record,
                           byte record_contents[], size_t record_len,
                           size_t pad_size,
                           volatile bool padding_bad,
                           u64bit record_sequence,
                           Protocol_Version record_version,
                           Record_Type record_type,
                           Connection_Cipher_State& cipherstate)
   {
   const size_t mac_size = cipherstate.mac_size();
   const size_t iv_size = cipherstate.iv_size();

   cipherstate.mac()->update_be(record_sequence);
   cipherstate.mac()->update(static_cast<byte>(record_type));

   if(cipherstate.mac_includes_record_version())
      {
      cipherstate.mac()->update(record_version.major_version());
      cipherstate.mac()->update(record_version.minor_version());
      }

   const size_t mac_pad_iv_size = mac_size + pad_size + iv_size;

   if(record_len < mac_pad_iv_size)
      throw Decoding_Error("Record sent with invalid length");

   const byte* plaintext_block = &record_contents[iv_size];
   const u16bit plaintext_length = record_len - mac_pad_iv_size;

   cipherstate.mac()->update_be(plaintext_length);
   cipherstate.mac()->update(plaintext_block, plaintext_length);

   std::vector<byte> mac_buf(mac_size);
   cipherstate.mac()->final(&mac_buf[0]);

   const size_t mac_offset = record_len - (mac_size + pad_size);

   const bool mac_bad = !same_mem(&record_contents[mac_offset], &mac_buf[0], mac_size);

   if(mac_bad || padding_bad)
      throw TLS_Exception(Alert::BAD_RECORD_MAC, "Message authentication failure");

   output_record = Record(record_sequence,
                          record_version,
                          record_type,
                          plaintext_block,
                          plaintext_length);

   return true;
   }

/*
* Checks the TLS padding. Returns 0 if the padding is invalid (we
* count the padding_length field as part of the padding size so a
* valid padding will always be at least one byte long), or the length
* of the padding otherwise. This is actually padding_length + 1
* because both the padding and padding_length fields are padding from
* our perspective.
*
* Returning 0 in the error case should ensure the MAC check will fail.
* This approach is suggested in section 6.2.3.2 of RFC 5246.
*
* Also returns 0 if block_size == 0, so can be safely called with a
* stream cipher in use.
*
* @fixme This should run in constant time
*/
size_t tls_padding_check(bool sslv3_padding,
                         size_t block_size,
                         const byte record[],
                         size_t record_len)
   {
   if(block_size == 0 || record_len == 0 || record_len % block_size != 0)
      return 0;

   const size_t padding_length = record[(record_len-1)];

   if(padding_length >= record_len)
      return 0;

   /*
   * SSL v3 requires that the padding be less than the block size
   * but not does specify the value of the padding bytes.
   */
   if(sslv3_padding)
      {
      if(padding_length > 0 && padding_length < block_size)
         return (padding_length + 1);
      else
         return 0;
      }

   /*
   * TLS v1.0 and up require all the padding bytes be the same value
   * and allows up to 255 bytes.
   */
   for(size_t i = 0; i != padding_length; ++i)
      if(record[(record_len-i-1)] != padding_length)
         return 0;

   return padding_length + 1;
   }

void cbc_decrypt_record(byte record_contents[], size_t record_len,
                        Connection_Cipher_State& cipherstate,
                        const BlockCipher& bc)
   {
   const size_t block_size = cipherstate.block_size();

   BOTAN_ASSERT(record_len % block_size == 0,
                "Buffer is an even multiple of block size");

   const size_t blocks = record_len / block_size;

   BOTAN_ASSERT(blocks >= 1, "At least one ciphertext block");

   byte* buf = record_contents;

   secure_vector<byte> last_ciphertext(block_size);
   copy_mem(&last_ciphertext[0], &buf[0], block_size);

   bc.decrypt(&buf[0]);
   xor_buf(&buf[0], &cipherstate.cbc_state()[0], block_size);

   secure_vector<byte> last_ciphertext2;

   for(size_t i = 1; i < blocks; ++i)
      {
      last_ciphertext2.assign(&buf[block_size*i], &buf[block_size*(i+1)]);
      bc.decrypt(&buf[block_size*i]);
      xor_buf(&buf[block_size*i], &last_ciphertext[0], block_size);
      std::swap(last_ciphertext, last_ciphertext2);
      }

   cipherstate.cbc_state() = last_ciphertext;
   }

bool decrypt_record(Record& output_record,
                    byte record_contents[], size_t record_len,
                    u64bit record_sequence,
                    Protocol_Version record_version,
                    Record_Type record_type,
                    Connection_Cipher_State& cipherstate)
   {
   volatile bool padding_bad = false;
   size_t pad_size = 0;

   if(StreamCipher* sc = cipherstate.stream_cipher())
      {
      sc->cipher1(record_contents, record_len);
      // no padding to check or remove
      }
   else if(BlockCipher* bc = cipherstate.block_cipher())
      {
      cbc_decrypt_record(record_contents, record_len, cipherstate, *bc);

      pad_size = tls_padding_check(cipherstate.cipher_padding_single_byte(),
                                   cipherstate.block_size(),
                                   record_contents, record_len);

      padding_bad = (pad_size == 0);
      }
   else
      {
      throw Internal_Error("No cipher state set but needed to decrypt");
      }

   return traditional_mac_check(output_record,
                                record_contents,
                                record_len,
                                pad_size,
                                padding_bad,
                                record_sequence,
                                record_version,
                                record_type,
                                cipherstate);
   }

}

size_t read_record(secure_vector<byte>& readbuf,
                   const byte input[],
                   size_t input_sz,
                   size_t& consumed,
                   Record& record,
                   Connection_Sequence_Numbers* sequence_numbers,
                   std::function<Connection_Cipher_State* (u16bit)> get_cipherstate)
   {
   consumed = 0;

   if(readbuf.size() < TLS_HEADER_SIZE) // header incomplete?
      {
      if(size_t needed = fill_buffer_to(readbuf,
                                        input, input_sz, consumed,
                                        TLS_HEADER_SIZE))
         return needed;

      BOTAN_ASSERT_EQUAL(readbuf.size(), TLS_HEADER_SIZE,
                         "Have an entire header");
      }

   // Possible SSLv2 format client hello
   if(!sequence_numbers && (readbuf[0] & 0x80) && (readbuf[2] == 1))
      {
      if(readbuf[3] == 0 && readbuf[4] == 2)
         throw TLS_Exception(Alert::PROTOCOL_VERSION,
                             "Client claims to only support SSLv2, rejecting");

      if(readbuf[3] >= 3) // SSLv2 mapped TLS hello, then?
         {
         const size_t record_len = make_u16bit(readbuf[0], readbuf[1]) & 0x7FFF;

         if(size_t needed = fill_buffer_to(readbuf,
                                           input, input_sz, consumed,
                                           record_len + 2))
            return needed;

         BOTAN_ASSERT_EQUAL(readbuf.size(), (record_len + 2),
                            "Have the entire SSLv2 hello");

         // Fake v3-style handshake message wrapper
         std::vector<byte> sslv2_hello(4 + readbuf.size() - 2);

         sslv2_hello[0] = CLIENT_HELLO_SSLV2;
         sslv2_hello[1] = 0;
         sslv2_hello[2] = readbuf[0] & 0x7F;
         sslv2_hello[3] = readbuf[1];

         copy_mem(&sslv2_hello[4], &readbuf[2], readbuf.size() - 2);

         record = Record(0,
                         Protocol_Version::TLS_V10,
                         HANDSHAKE,
                         std::move(sslv2_hello));

         readbuf.clear();
         return 0;
         }
      }

   Protocol_Version record_version = Protocol_Version(readbuf[1], readbuf[2]);

   const bool is_dtls = record_version.is_datagram_protocol();

   if(is_dtls && readbuf.size() < DTLS_HEADER_SIZE)
      {
      if(size_t needed = fill_buffer_to(readbuf,
                                        input, input_sz, consumed,
                                        DTLS_HEADER_SIZE))
         return needed;

      BOTAN_ASSERT_EQUAL(readbuf.size(), DTLS_HEADER_SIZE,
                         "Have an entire header");
      }

   const size_t header_size = (is_dtls) ? DTLS_HEADER_SIZE : TLS_HEADER_SIZE;

   const size_t record_len = make_u16bit(readbuf[header_size-2],
                                         readbuf[header_size-1]);

   if(record_len > MAX_CIPHERTEXT_SIZE)
      throw TLS_Exception(Alert::RECORD_OVERFLOW,
                          "Got message that exceeds maximum size");

   if(size_t needed = fill_buffer_to(readbuf,
                                     input, input_sz, consumed,
                                     header_size + record_len))
      return needed; // wrong for DTLS?

   BOTAN_ASSERT_EQUAL(static_cast<size_t>(header_size) + record_len,
                      readbuf.size(),
                      "Have the full record");

   Record_Type record_type = static_cast<Record_Type>(readbuf[0]);

   u64bit record_sequence = 0;
   u16bit epoch = 0;

   if(is_dtls)
      {
      record_sequence = load_be<u64bit>(&readbuf[3], 0);
      epoch = (record_sequence >> 48);
      }
   else if(sequence_numbers)
      {
      record_sequence = sequence_numbers->next_read_sequence();
      epoch = sequence_numbers->current_read_epoch();
      }
   else
      {
      // server initial handshake case
      record_sequence = 0;
      epoch = 0;
      }

   if(sequence_numbers && sequence_numbers->already_seen(record_sequence))
      return 0;

   byte* record_contents = &readbuf[header_size];

   if(epoch == 0) // Unencrypted initial handshake
      {
      record = Record(record_sequence,
                      record_version,
                      record_type,
                      &readbuf[header_size],
                      record_len);

      readbuf.clear();
      return 0; // got a full record
      }

   // Otherwise, decrypt, check MAC, return plaintext
   Connection_Cipher_State* cipherstate = get_cipherstate(epoch);

   // FIXME: DTLS reordering might cause us not to have the cipher state

   BOTAN_ASSERT(cipherstate, "Have cipherstate for this epoch");

   const bool ok = decrypt_record(record,
                                  record_contents,
                                  record_len,
                                  record_sequence,
                                  record_version,
                                  record_type,
                                  *cipherstate);

   if(ok && sequence_numbers)
      sequence_numbers->read_accept(record_sequence);

   readbuf.clear();
   return 0;
   }

}

}