ccm.cpp

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/*
* CCM Mode Encryption
* (C) 2013,2018 Jack Lloyd
* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/internal/ccm.h>
 
#include <botan/exceptn.h>
#include <botan/mem_ops.h>
#include <botan/internal/ct_utils.h>
#include <botan/internal/fmt.h>
#include <botan/internal/int_utils.h>
#include <botan/internal/loadstor.h>
 
namespace Botan {
 
// 128-bit cipher is intrinsic to CCM definition
static const size_t CCM_BS = 16;
 
/*
* CCM_Mode Constructor
*/
CCM_Mode::CCM_Mode(std::unique_ptr<BlockCipher> cipher, size_t tag_size, size_t L) :
      m_tag_size(tag_size), m_L(L), m_cipher(std::move(cipher)) {
   if(m_cipher->block_size() != CCM_BS) {
      throw Invalid_Argument(m_cipher->name() + " cannot be used with CCM mode");
   }
 
   if(L < 2 || L > 8) {
      throw Invalid_Argument(fmt("Invalid CCM L value {}", L));
   }
 
   if(tag_size < 4 || tag_size > 16 || tag_size % 2 != 0) {
      throw Invalid_Argument(fmt("Invalid CCM tag length {}", tag_size));
   }
}
 
void CCM_Mode::clear() {
   m_cipher->clear();
   m_ad_buf.clear();
   reset();
}
 
void CCM_Mode::reset() {
   m_nonce.clear();
   m_msg_buf.clear();
}
 
std::string CCM_Mode::name() const {
   return fmt("{}/CCM({},{})", m_cipher->name(), tag_size(), L());
}
 
bool CCM_Mode::valid_nonce_length(size_t length) const {
   return (length == (15 - L()));
}
 
size_t CCM_Mode::default_nonce_length() const {
   return (15 - L());
}
 
size_t CCM_Mode::update_granularity() const {
   return 1;
}
 
size_t CCM_Mode::ideal_granularity() const {
   // Completely arbitrary
   return m_cipher->parallel_bytes();
}
 
bool CCM_Mode::requires_entire_message() const {
   return true;
}
 
Key_Length_Specification CCM_Mode::key_spec() const {
   return m_cipher->key_spec();
}
 
bool CCM_Mode::has_keying_material() const {
   return m_cipher->has_keying_material();
}
 
void CCM_Mode::key_schedule(std::span<const uint8_t> key) {
   m_cipher->set_key(key);
   // Clear any per-message state; AD is preserved per AEAD contract
   // (CCM advertises associated_data_requires_key() == false).
   reset();
}
 
void CCM_Mode::set_associated_data_n(size_t idx, std::span<const uint8_t> ad) {
   BOTAN_ARG_CHECK(idx == 0, "CCM: cannot handle non-zero index in set_associated_data_n");
   BOTAN_STATE_CHECK(m_nonce.empty());
 
   m_ad_buf.clear();
 
   if(!ad.empty()) {
      // FIXME: support larger AD using length encoding rules
      BOTAN_ARG_CHECK(ad.size() < (0xFFFF - 0xFF), "Supported CCM AD length");
 
      m_ad_buf.push_back(get_byte<0>(static_cast<uint16_t>(ad.size())));
      m_ad_buf.push_back(get_byte<1>(static_cast<uint16_t>(ad.size())));
      m_ad_buf.insert(m_ad_buf.end(), ad.begin(), ad.end());
      while(m_ad_buf.size() % CCM_BS != 0) {
         m_ad_buf.push_back(0);  // pad with zeros to full block size
      }
   }
}
 
void CCM_Mode::start_msg(const uint8_t nonce[], size_t nonce_len) {
   BOTAN_STATE_CHECK(m_nonce.empty());
 
   if(!valid_nonce_length(nonce_len)) {
      throw Invalid_IV_Length(name(), nonce_len);
   }
 
   m_nonce.assign(nonce, nonce + nonce_len);
   m_msg_buf.clear();
}
 
size_t CCM_Mode::process_msg(uint8_t buf[], size_t sz) {
   BOTAN_STATE_CHECK(!m_nonce.empty());
   m_msg_buf.insert(m_msg_buf.end(), buf, buf + sz);
 
   // CCM message length is limited to 2^(8*L) - 1 bytes
   if(L() < 8) {
      const uint64_t max_msg_len = (static_cast<uint64_t>(1) << (8 * L())) - 1;
      if(m_msg_buf.size() > max_msg_len) {
         throw Invalid_State("CCM message length exceeds the limit for L");
      }
   }
 
   return 0;  // no output until finished
}
 
void CCM_Mode::encode_length(uint64_t len, uint8_t out[]) {
   const size_t len_bytes = L();
 
   BOTAN_ASSERT_NOMSG(len_bytes >= 2 && len_bytes <= 8);
 
   for(size_t i = 0; i != len_bytes; ++i) {
      out[len_bytes - 1 - i] = get_byte_var(sizeof(uint64_t) - 1 - i, len);
   }
 
   if(len_bytes < 8 && (len >> (len_bytes * 8)) > 0) {
      throw Encoding_Error("CCM message length too long to encode in L field");
   }
}
 
void CCM_Mode::inc(secure_vector<uint8_t>& C) {
   for(size_t i = 0; i != C.size(); ++i) {
      uint8_t& b = C[C.size() - i - 1];
      b += 1;
      if(b > 0) {
         break;
      }
   }
}
 
secure_vector<uint8_t> CCM_Mode::format_b0(size_t sz) {
   if(m_nonce.size() != 15 - L()) {
      throw Invalid_State("CCM mode must set nonce");
   }
   secure_vector<uint8_t> B0(CCM_BS);
 
   const uint8_t b_flags =
      static_cast<uint8_t>((!m_ad_buf.empty() ? 64 : 0) + (((tag_size() / 2) - 1) << 3) + (L() - 1));
 
   B0[0] = b_flags;
   copy_mem(&B0[1], m_nonce.data(), m_nonce.size());
   encode_length(sz, &B0[m_nonce.size() + 1]);
 
   return B0;
}
 
secure_vector<uint8_t> CCM_Mode::format_c0() {
   if(m_nonce.size() != 15 - L()) {
      throw Invalid_State("CCM mode must set nonce");
   }
   secure_vector<uint8_t> C(CCM_BS);
 
   const uint8_t a_flags = static_cast<uint8_t>(L() - 1);
 
   C[0] = a_flags;
   copy_mem(&C[1], m_nonce.data(), m_nonce.size());
 
   return C;
}
 
size_t CCM_Encryption::output_length(size_t input_length) const {
   return add_or_throw(input_length, tag_size(), "CCM input too large");
}
 
void CCM_Encryption::finish_msg(secure_vector<uint8_t>& buffer, size_t offset) {
   BOTAN_ARG_CHECK(buffer.size() >= offset, "Offset is out of range");
 
   buffer.insert(buffer.begin() + offset, msg_buf().begin(), msg_buf().end());
 
   const size_t sz = buffer.size() - offset;
   uint8_t* buf = buffer.data() + offset;
 
   const secure_vector<uint8_t>& ad = ad_buf();
   BOTAN_ARG_CHECK(ad.size() % CCM_BS == 0, "AD is block size multiple");
 
   const BlockCipher& E = cipher();
 
   secure_vector<uint8_t> T(CCM_BS);
   E.encrypt(format_b0(sz), T);
 
   for(size_t i = 0; i != ad.size(); i += CCM_BS) {
      xor_buf(T.data(), &ad[i], CCM_BS);
      E.encrypt(T);
   }
 
   secure_vector<uint8_t> C = format_c0();
   secure_vector<uint8_t> S0(CCM_BS);
   E.encrypt(C, S0);
   inc(C);
 
   secure_vector<uint8_t> X(CCM_BS);
 
   const uint8_t* buf_end = &buf[sz];
 
   while(buf != buf_end) {
      const size_t to_proc = std::min<size_t>(CCM_BS, buf_end - buf);
 
      xor_buf(T.data(), buf, to_proc);
      E.encrypt(T);
 
      E.encrypt(C, X);
      xor_buf(buf, X.data(), to_proc);
      inc(C);
 
      buf += to_proc;
   }
 
   T ^= S0;
 
   buffer += std::make_pair(T.data(), tag_size());
 
   reset();
}
 
size_t CCM_Decryption::output_length(size_t input_length) const {
   BOTAN_ARG_CHECK(input_length >= tag_size(), "Message too short to be valid");
   return input_length - tag_size();
}
 
void CCM_Decryption::finish_msg(secure_vector<uint8_t>& buffer, size_t offset) {
   BOTAN_ARG_CHECK(buffer.size() >= offset, "Offset is out of range");
 
   buffer.insert(buffer.begin() + offset, msg_buf().begin(), msg_buf().end());
 
   const size_t sz = buffer.size() - offset;
   uint8_t* buf = buffer.data() + offset;
 
   BOTAN_ARG_CHECK(sz >= tag_size(), "input did not include the tag");
 
   const secure_vector<uint8_t>& ad = ad_buf();
   BOTAN_ARG_CHECK(ad.size() % CCM_BS == 0, "AD is block size multiple");
 
   const BlockCipher& E = cipher();
 
   secure_vector<uint8_t> T(CCM_BS);
   E.encrypt(format_b0(sz - tag_size()), T);
 
   for(size_t i = 0; i != ad.size(); i += CCM_BS) {
      xor_buf(T.data(), &ad[i], CCM_BS);
      E.encrypt(T);
   }
 
   secure_vector<uint8_t> C = format_c0();
 
   secure_vector<uint8_t> S0(CCM_BS);
   E.encrypt(C, S0);
   inc(C);
 
   secure_vector<uint8_t> X(CCM_BS);
 
   const uint8_t* buf_end = &buf[sz - tag_size()];
 
   while(buf != buf_end) {
      const size_t to_proc = std::min<size_t>(CCM_BS, buf_end - buf);
 
      E.encrypt(C, X);
      xor_buf(buf, X.data(), to_proc);
      inc(C);
 
      xor_buf(T.data(), buf, to_proc);
      E.encrypt(T);
 
      buf += to_proc;
   }
 
   T ^= S0;
 
   if(!CT::is_equal(T.data(), buf_end, tag_size()).as_bool()) {
      clear_mem(std::span{buffer}.subspan(offset, sz - tag_size()));
      // Reset on the failure path too, matching GCM/SIV/ChaCha20Poly1305, so a
      // failed decryptor is reusable rather than stuck in a partial state.
      reset();
      throw Invalid_Authentication_Tag("CCM tag check failed");
   }
 
   buffer.resize(buffer.size() - tag_size());
 
   reset();
}
 
}  // namespace Botan