/*

* EAX Mode Encryption

* (C) 1999-2007 Jack Lloyd

* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#include <botan/internal/eax.h>

#include <botan/mem_ops.h>

#include <botan/internal/cmac.h>

#include <botan/internal/ct_utils.h>

#include <botan/internal/ctr.h>

#include <botan/internal/fmt.h>

namespace Botan {

namespace {

/*

* EAX MAC-based PRF

*/

secure_vector<uint8_t> eax_prf(

   uint8_t tag, size_t block_size, MessageAuthenticationCode& mac, const uint8_t in[], size_t length) {

   for(size_t i = 0; i != block_size - 1; ++i) {

      mac.update(0);

   }

   mac.update(tag);

   mac.update(in, length);

   return mac.final();

}

}  // namespace

/*

* EAX_Mode Constructor

*/

EAX_Mode::EAX_Mode(std::unique_ptr<BlockCipher> cipher, size_t tag_size) :

      m_tag_size(tag_size),

      m_cipher(std::move(cipher)),

      m_ctr(std::make_unique<CTR_BE>(m_cipher->new_object())),

      m_cmac(std::make_unique<CMAC>(m_cipher->new_object())) {

   if(m_tag_size < 8 || m_tag_size > m_cmac->output_length()) {

      throw Invalid_Argument(fmt("Tag size {} is not allowed for {}", tag_size, name()));

   }

}

void EAX_Mode::clear() {

   m_cipher->clear();

   m_ctr->clear();

   m_cmac->clear();

   reset();

}

void EAX_Mode::reset() {

   m_ad_mac.clear();

   m_nonce_mac.clear();

   // Clear out any data added to the CMAC calculation

   try {

      m_cmac->final();

   } catch(Key_Not_Set&) {}

}

std::string EAX_Mode::name() const {

   return (m_cipher->name() + "/EAX");

}

size_t EAX_Mode::update_granularity() const {

   return 1;

}

size_t EAX_Mode::ideal_granularity() const {

   return m_cipher->parallel_bytes();

}

Key_Length_Specification EAX_Mode::key_spec() const {

   return m_ctr->key_spec();

}

bool EAX_Mode::has_keying_material() const {

   return m_ctr->has_keying_material() && m_cmac->has_keying_material();

}

/*

* Set the EAX key

*/

void EAX_Mode::key_schedule(std::span<const uint8_t> key) {

   /*

   * These could share the key schedule, which is one nice part of EAX,

   * but it's much easier to ignore that here...

   */

   m_ctr->set_key(key);

   m_cmac->set_key(key);

}

/*

* Set the EAX associated data

*/

void EAX_Mode::set_associated_data_n(size_t idx, std::span<const uint8_t> ad) {

   BOTAN_ARG_CHECK(idx == 0, "EAX: cannot handle non-zero index in set_associated_data_n");

   if(!m_nonce_mac.empty()) {

      throw Invalid_State("Cannot set AD for EAX while processing a message");

   }

   m_ad_mac = eax_prf(1, block_size(), *m_cmac, ad.data(), ad.size());

}

void EAX_Mode::start_msg(const uint8_t nonce[], size_t nonce_len) {

   if(!valid_nonce_length(nonce_len)) {

      throw Invalid_IV_Length(name(), nonce_len);

   }

   m_nonce_mac = eax_prf(0, block_size(), *m_cmac, nonce, nonce_len);

   m_ctr->set_iv(m_nonce_mac.data(), m_nonce_mac.size());

   for(size_t i = 0; i != block_size() - 1; ++i) {

      m_cmac->update(0);

   }

   m_cmac->update(2);

}

size_t EAX_Encryption::process_msg(uint8_t buf[], size_t sz) {

   BOTAN_STATE_CHECK(!m_nonce_mac.empty());

   m_ctr->cipher(buf, buf, sz);

   m_cmac->update(buf, sz);

   return sz;

}

void EAX_Encryption::finish_msg(secure_vector<uint8_t>& buffer, size_t offset) {

   BOTAN_STATE_CHECK(!m_nonce_mac.empty());

   update(buffer, offset);

   secure_vector<uint8_t> data_mac = m_cmac->final();

   xor_buf(data_mac, m_nonce_mac, data_mac.size());

   if(m_ad_mac.empty()) {

      m_ad_mac = eax_prf(1, block_size(), *m_cmac, nullptr, 0);

   }

   xor_buf(data_mac, m_ad_mac, data_mac.size());

   buffer += std::make_pair(data_mac.data(), tag_size());

   m_nonce_mac.clear();

}

size_t EAX_Decryption::process_msg(uint8_t buf[], size_t sz) {

   BOTAN_STATE_CHECK(!m_nonce_mac.empty());

   m_cmac->update(buf, sz);

   m_ctr->cipher(buf, buf, sz);

   return sz;

}

void EAX_Decryption::finish_msg(secure_vector<uint8_t>& buffer, size_t offset) {

   BOTAN_STATE_CHECK(!m_nonce_mac.empty());

   BOTAN_ARG_CHECK(buffer.size() >= offset, "Offset is out of range");

   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 size_t remaining = sz - tag_size();

   if(remaining > 0) {

      m_cmac->update(buf, remaining);

      m_ctr->cipher(buf, buf, remaining);

   }

   const uint8_t* included_tag = &buf[remaining];

   secure_vector<uint8_t> mac = m_cmac->final();

   mac ^= m_nonce_mac;

   if(m_ad_mac.empty()) {

      m_ad_mac = eax_prf(1, block_size(), *m_cmac, nullptr, 0);

   }

   mac ^= m_ad_mac;

   const bool accept_mac = CT::is_equal(mac.data(), included_tag, tag_size()).as_bool();

   buffer.resize(offset + remaining);

   m_nonce_mac.clear();

   if(!accept_mac) {

      throw Invalid_Authentication_Tag("EAX tag check failed");

   }

}

}  // namespace Botan