tls_record.cpp

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/*
* TLS Record Handling
* (C) 2012,2013,2014,2015,2016,2019 Jack Lloyd
*     2016 Juraj Somorovsky
*     2016 Matthias Gierlings
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/internal/tls_record.h>
 
#include <botan/rng.h>
#include <botan/tls_callbacks.h>
#include <botan/tls_ciphersuite.h>
#include <botan/tls_exceptn.h>
#include <botan/internal/ct_utils.h>
#include <botan/internal/loadstor.h>
#include <botan/internal/tls_seq_numbers.h>
#include <botan/internal/tls_session_key.h>
#include <sstream>
 
#if defined(BOTAN_HAS_TLS_CBC)
   #include <botan/internal/tls_cbc.h>
#endif
 
namespace Botan::TLS {
 
Connection_Cipher_State::Connection_Cipher_State(Protocol_Version version,
                                                 Connection_Side side,
                                                 bool our_side,
                                                 const Ciphersuite& suite,
                                                 const Session_Keys& keys,
                                                 bool uses_encrypt_then_mac) {
   m_nonce_format = suite.nonce_format();
   m_nonce_bytes_from_record = suite.nonce_bytes_from_record(version);
   m_nonce_bytes_from_handshake = suite.nonce_bytes_from_handshake();
 
   const secure_vector<uint8_t>& aead_key = keys.aead_key(side);
   m_nonce = keys.nonce(side);
 
   BOTAN_ASSERT_NOMSG(m_nonce.size() == m_nonce_bytes_from_handshake);
 
   if(nonce_format() == Nonce_Format::CBC_MODE) {
#if defined(BOTAN_HAS_TLS_CBC)
      // legacy CBC+HMAC mode
      auto mac = MessageAuthenticationCode::create_or_throw("HMAC(" + suite.mac_algo() + ")");
      auto cipher = BlockCipher::create_or_throw(suite.cipher_algo());
 
      if(our_side) {
         m_aead = std::make_unique<TLS_CBC_HMAC_AEAD_Encryption>(std::move(cipher),
                                                                 std::move(mac),
                                                                 suite.cipher_keylen(),
                                                                 suite.mac_keylen(),
                                                                 version,
                                                                 uses_encrypt_then_mac);
      } else {
         m_aead = std::make_unique<TLS_CBC_HMAC_AEAD_Decryption>(std::move(cipher),
                                                                 std::move(mac),
                                                                 suite.cipher_keylen(),
                                                                 suite.mac_keylen(),
                                                                 version,
                                                                 uses_encrypt_then_mac);
      }
 
#else
      BOTAN_UNUSED(uses_encrypt_then_mac);
      throw Internal_Error("Negotiated disabled TLS CBC+HMAC ciphersuite");
#endif
   } else {
      m_aead =
         AEAD_Mode::create_or_throw(suite.cipher_algo(), our_side ? Cipher_Dir::Encryption : Cipher_Dir::Decryption);
   }
 
   m_aead->set_key(aead_key);
}
 
std::vector<uint8_t> Connection_Cipher_State::aead_nonce(uint64_t seq, RandomNumberGenerator& rng) {
   switch(m_nonce_format) {
      case Nonce_Format::CBC_MODE: {
         if(!m_nonce.empty()) {
            std::vector<uint8_t> nonce;
            nonce.swap(m_nonce);
            return nonce;
         }
         std::vector<uint8_t> nonce(nonce_bytes_from_record());
         rng.randomize(nonce.data(), nonce.size());
         return nonce;
      }
      case Nonce_Format::AEAD_XOR_12: {
         std::vector<uint8_t> nonce(12);
         store_be(seq, nonce.data() + 4);
         xor_buf(nonce, m_nonce.data(), m_nonce.size());
         return nonce;
      }
      case Nonce_Format::AEAD_IMPLICIT_4: {
         BOTAN_ASSERT_NOMSG(m_nonce.size() == 4);
         std::vector<uint8_t> nonce(12);
         copy_mem(&nonce[0], m_nonce.data(), 4);
         store_be(seq, &nonce[nonce_bytes_from_handshake()]);
         return nonce;
      }
   }
 
   throw Invalid_State("Unknown nonce format specified");
}
 
std::vector<uint8_t> Connection_Cipher_State::aead_nonce(const uint8_t record[], size_t record_len, uint64_t seq) {
   switch(m_nonce_format) {
      case Nonce_Format::CBC_MODE: {
         if(nonce_bytes_from_record() == 0 && !m_nonce.empty()) {
            std::vector<uint8_t> nonce;
            nonce.swap(m_nonce);
            return nonce;
         }
         if(record_len < nonce_bytes_from_record()) {
            throw Decoding_Error("Invalid CBC packet too short to be valid");
         }
         std::vector<uint8_t> nonce(record, record + nonce_bytes_from_record());
         return nonce;
      }
      case Nonce_Format::AEAD_XOR_12: {
         std::vector<uint8_t> nonce(12);
         store_be(seq, nonce.data() + 4);
         xor_buf(nonce, m_nonce.data(), m_nonce.size());
         return nonce;
      }
      case Nonce_Format::AEAD_IMPLICIT_4: {
         BOTAN_ASSERT_NOMSG(m_nonce.size() == 4);
         if(record_len < nonce_bytes_from_record()) {
            throw Decoding_Error("Invalid AEAD packet too short to be valid");
         }
         std::vector<uint8_t> nonce(12);
         copy_mem(&nonce[0], m_nonce.data(), 4);
         copy_mem(&nonce[nonce_bytes_from_handshake()], record, nonce_bytes_from_record());
         return nonce;
      }
   }
 
   throw Invalid_State("Unknown nonce format specified");
}
 
std::vector<uint8_t> Connection_Cipher_State::format_ad(uint64_t msg_sequence,
                                                        Record_Type msg_type,
                                                        Protocol_Version version,
                                                        uint16_t msg_length) {
   std::vector<uint8_t> ad(13);
 
   store_be(msg_sequence, &ad[0]);
   ad[8] = static_cast<uint8_t>(msg_type);
   ad[9] = version.major_version();
   ad[10] = version.minor_version();
   ad[11] = get_byte<0>(msg_length);
   ad[12] = get_byte<1>(msg_length);
 
   return ad;
}
 
namespace {
 
inline void append_u16_len(secure_vector<uint8_t>& output, size_t len_field) {
   const uint16_t len16 = static_cast<uint16_t>(len_field);
   BOTAN_ASSERT_EQUAL(len_field, len16, "No truncation");
   output.push_back(get_byte<0>(len16));
   output.push_back(get_byte<1>(len16));
}
 
void write_record_header(secure_vector<uint8_t>& output,
                         Record_Type record_type,
                         Protocol_Version version,
                         uint64_t record_sequence) {
   output.clear();
 
   output.push_back(static_cast<uint8_t>(record_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_var(i, record_sequence));
      }
   }
}
 
}  // namespace
 
void write_unencrypted_record(secure_vector<uint8_t>& output,
                              Record_Type record_type,
                              Protocol_Version version,
                              uint64_t record_sequence,
                              const uint8_t* message,
                              size_t message_len) {
   if(record_type == Record_Type::ApplicationData) {
      throw Internal_Error("Writing an unencrypted TLS application data record");
   }
   write_record_header(output, record_type, version, record_sequence);
   append_u16_len(output, message_len);
   output.insert(output.end(), message, message + message_len);
}
 
void write_record(secure_vector<uint8_t>& output,
                  Record_Type record_type,
                  Protocol_Version version,
                  uint64_t record_sequence,
                  const uint8_t* message,
                  size_t message_len,
                  Connection_Cipher_State& cs,
                  RandomNumberGenerator& rng) {
   write_record_header(output, record_type, version, record_sequence);
 
   AEAD_Mode& aead = cs.aead();
   std::vector<uint8_t> aad = cs.format_ad(record_sequence, record_type, version, static_cast<uint16_t>(message_len));
 
   const size_t ctext_size = aead.output_length(message_len);
 
   const size_t rec_size = ctext_size + cs.nonce_bytes_from_record();
 
   aead.set_associated_data(aad);
 
   const std::vector<uint8_t> nonce = cs.aead_nonce(record_sequence, rng);
 
   append_u16_len(output, rec_size);
 
   if(cs.nonce_bytes_from_record() > 0) {
      if(cs.nonce_format() == Nonce_Format::CBC_MODE) {
         output += nonce;
      } else {
         output += std::make_pair(&nonce[cs.nonce_bytes_from_handshake()], cs.nonce_bytes_from_record());
      }
   }
 
   const size_t header_size = output.size();
   output += std::make_pair(message, message_len);
 
   aead.start(nonce);
   aead.finish(output, header_size);
 
   BOTAN_ASSERT(output.size() < MAX_CIPHERTEXT_SIZE, "Produced ciphertext larger than protocol allows");
}
 
namespace {
 
size_t fill_buffer_to(
   secure_vector<uint8_t>& readbuf, const uint8_t*& 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, input + taken);
   input_consumed += taken;
   input_size -= taken;
   input += taken;
 
   return (desired - readbuf.size());  // how many bytes do we still need?
}
 
void decrypt_record(secure_vector<uint8_t>& output,
                    uint8_t record_contents[],
                    size_t record_len,
                    uint64_t record_sequence,
                    Protocol_Version record_version,
                    Record_Type record_type,
                    Connection_Cipher_State& cs) {
   AEAD_Mode& aead = cs.aead();
 
   const std::vector<uint8_t> nonce = cs.aead_nonce(record_contents, record_len, record_sequence);
   const uint8_t* msg = &record_contents[cs.nonce_bytes_from_record()];
   const size_t msg_length = record_len - cs.nonce_bytes_from_record();
 
   /*
   * This early rejection is based just on public information (length of the
   * encrypted packet) and so does not leak any information. We used to use
   * decode_error here which really is more appropriate, but that confuses some
   * tools which are attempting automated detection of padding oracles,
   * including older versions of TLS-Attacker.
   */
   if(msg_length < aead.minimum_final_size()) {
      throw TLS_Exception(Alert::BadRecordMac, "AEAD packet is shorter than the tag");
   }
 
   const size_t ptext_size = aead.output_length(msg_length);
 
   aead.set_associated_data(
      cs.format_ad(record_sequence, record_type, record_version, static_cast<uint16_t>(ptext_size)));
 
   aead.start(nonce);
 
   output.assign(msg, msg + msg_length);
   aead.finish(output, 0);
}
 
Record_Header read_tls_record(secure_vector<uint8_t>& readbuf,
                              const uint8_t input[],
                              size_t input_len,
                              size_t& consumed,
                              secure_vector<uint8_t>& recbuf,
                              Connection_Sequence_Numbers* sequence_numbers,
                              const get_cipherstate_fn& get_cipherstate) {
   if(readbuf.size() < TLS_HEADER_SIZE) {
      // header incomplete
      if(size_t needed = fill_buffer_to(readbuf, input, input_len, consumed, TLS_HEADER_SIZE)) {
         return Record_Header(needed);
      }
 
      BOTAN_ASSERT_EQUAL(readbuf.size(), TLS_HEADER_SIZE, "Have an entire header");
   }
 
   /*
   Verify that the record type and record version are within some expected
   range, so we can quickly reject totally invalid packets.
 
   The version check is a little hacky but given how TLS 1.3 versioning works
   this is probably safe
 
   - The first byte is the record version which in TLS 1.2 is always in [20..23)
   - The second byte is the TLS major version which is effectively fossilized at 3
   - The third byte is the TLS minor version which (due to TLS 1.3 versioning changes)
     will never be more than 3 (signifying TLS 1.2)
   */
   const bool bad_record_type = readbuf[0] < 20 || readbuf[0] > 23;
   const bool bad_record_version = readbuf[1] != 3 || readbuf[2] >= 4;
 
   if(bad_record_type || bad_record_version) {
      // We know we read up to at least the 5 byte TLS header
      const std::string first5 = std::string(reinterpret_cast<const char*>(readbuf.data()), 5);
 
      if(first5 == "GET /" || first5 == "PUT /" || first5 == "POST " || first5 == "HEAD ") {
         throw TLS_Exception(Alert::ProtocolVersion, "Client sent plaintext HTTP request instead of TLS handshake");
      }
 
      if(first5 == "CONNE") {
         throw TLS_Exception(Alert::ProtocolVersion,
                             "Client sent plaintext HTTP proxy CONNECT request instead of TLS handshake");
      }
 
      if(bad_record_type) {
         // RFC 5246 Section 6.
         //   If a TLS implementation receives an unexpected record type, it MUST
         //   send an unexpected_message alert.
         throw TLS_Exception(Alert::UnexpectedMessage, "TLS record type had unexpected value");
      }
      throw TLS_Exception(Alert::ProtocolVersion, "TLS record version had unexpected value");
   }
 
   const Protocol_Version version(readbuf[1], readbuf[2]);
 
   if(version.is_datagram_protocol()) {
      throw TLS_Exception(Alert::ProtocolVersion, "Expected TLS but got a record with DTLS version");
   }
 
   const size_t record_size = make_uint16(readbuf[TLS_HEADER_SIZE - 2], readbuf[TLS_HEADER_SIZE - 1]);
 
   if(record_size > MAX_CIPHERTEXT_SIZE) {
      throw TLS_Exception(Alert::RecordOverflow, "Received a record that exceeds maximum size");
   }
 
   if(record_size == 0) {
      throw TLS_Exception(Alert::DecodeError, "Received a completely empty record");
   }
 
   if(size_t needed = fill_buffer_to(readbuf, input, input_len, consumed, TLS_HEADER_SIZE + record_size)) {
      return Record_Header(needed);
   }
 
   BOTAN_ASSERT_EQUAL(static_cast<size_t>(TLS_HEADER_SIZE) + record_size, readbuf.size(), "Have the full record");
 
   const Record_Type type = static_cast<Record_Type>(readbuf[0]);
 
   uint16_t epoch = 0;
 
   uint64_t sequence = 0;
   if(sequence_numbers) {
      sequence = sequence_numbers->next_read_sequence();
      epoch = sequence_numbers->current_read_epoch();
   } else {
      // server initial handshake case
      epoch = 0;
   }
 
   if(epoch == 0) {
      // Unencrypted initial handshake
      recbuf.assign(readbuf.begin() + TLS_HEADER_SIZE, readbuf.begin() + TLS_HEADER_SIZE + record_size);
      readbuf.clear();
      return Record_Header(sequence, version, type);
   }
 
   // Otherwise, decrypt, check MAC, return plaintext
   auto cs = get_cipherstate(epoch);
 
   BOTAN_ASSERT(cs, "Have cipherstate for this epoch");
 
   decrypt_record(recbuf, &readbuf[TLS_HEADER_SIZE], record_size, sequence, version, type, *cs);
 
   if(sequence_numbers) {
      sequence_numbers->read_accept(sequence);
   }
 
   readbuf.clear();
   return Record_Header(sequence, version, type);
}
 
Record_Header read_dtls_record(secure_vector<uint8_t>& readbuf,
                               const uint8_t input[],
                               size_t input_len,
                               size_t& consumed,
                               secure_vector<uint8_t>& recbuf,
                               Connection_Sequence_Numbers* sequence_numbers,
                               const get_cipherstate_fn& get_cipherstate,
                               bool allow_epoch0_restart) {
   if(readbuf.size() < DTLS_HEADER_SIZE) {
      // header incomplete
      if(fill_buffer_to(readbuf, input, input_len, consumed, DTLS_HEADER_SIZE)) {
         readbuf.clear();
         return Record_Header(0);
      }
 
      BOTAN_ASSERT_EQUAL(readbuf.size(), DTLS_HEADER_SIZE, "Have an entire header");
   }
 
   const Protocol_Version version(readbuf[1], readbuf[2]);
 
   if(version.is_datagram_protocol() == false) {
      readbuf.clear();
      return Record_Header(0);
   }
 
   const size_t record_size = make_uint16(readbuf[DTLS_HEADER_SIZE - 2], readbuf[DTLS_HEADER_SIZE - 1]);
 
   if(record_size > MAX_CIPHERTEXT_SIZE) {
      // Too large to be valid, ignore it
      readbuf.clear();
      return Record_Header(0);
   }
 
   if(fill_buffer_to(readbuf, input, input_len, consumed, DTLS_HEADER_SIZE + record_size)) {
      // Truncated packet?
      readbuf.clear();
      return Record_Header(0);
   }
 
   BOTAN_ASSERT_EQUAL(static_cast<size_t>(DTLS_HEADER_SIZE) + record_size, readbuf.size(), "Have the full record");
 
   const Record_Type type = static_cast<Record_Type>(readbuf[0]);
 
   const uint64_t sequence = load_be<uint64_t>(&readbuf[3], 0);
   const uint16_t epoch = (sequence >> 48);
 
   const bool already_seen = sequence_numbers && sequence_numbers->already_seen(sequence);
 
   if(already_seen && !(epoch == 0 && allow_epoch0_restart)) {
      readbuf.clear();
      return Record_Header(0);
   }
 
   if(epoch == 0) {
      // Unencrypted initial handshake
      recbuf.assign(readbuf.begin() + DTLS_HEADER_SIZE, readbuf.begin() + DTLS_HEADER_SIZE + record_size);
      readbuf.clear();
      if(sequence_numbers) {
         sequence_numbers->read_accept(sequence);
      }
      return Record_Header(sequence, version, type);
   }
 
   try {
      // Otherwise, decrypt, check MAC, return plaintext
      auto cs = get_cipherstate(epoch);
 
      BOTAN_ASSERT(cs, "Have cipherstate for this epoch");
 
      decrypt_record(recbuf, &readbuf[DTLS_HEADER_SIZE], record_size, sequence, version, type, *cs);
   } catch(std::exception&) {
      readbuf.clear();
      return Record_Header(0);
   }
 
   if(sequence_numbers) {
      sequence_numbers->read_accept(sequence);
   }
 
   readbuf.clear();
   return Record_Header(sequence, version, type);
}
 
}  // namespace
 
Record_Header read_record(bool is_datagram,
                          secure_vector<uint8_t>& readbuf,
                          const uint8_t input[],
                          size_t input_len,
                          size_t& consumed,
                          secure_vector<uint8_t>& recbuf,
                          Connection_Sequence_Numbers* sequence_numbers,
                          const get_cipherstate_fn& get_cipherstate,
                          bool allow_epoch0_restart) {
   if(is_datagram) {
      return read_dtls_record(
         readbuf, input, input_len, consumed, recbuf, sequence_numbers, get_cipherstate, allow_epoch0_restart);
   } else {
      return read_tls_record(readbuf, input, input_len, consumed, recbuf, sequence_numbers, get_cipherstate);
   }
}
 
}  // namespace Botan::TLS