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/*
* EAX Mode Encryption
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/eax.h>
#include <botan/cmac.h>
#include <botan/ctr.h>
#include <botan/parsing.h>
#include <botan/internal/xor_buf.h>
#include <algorithm>
namespace Botan {
namespace {
/*
* EAX MAC-based PRF
*/
secure_vector<byte> eax_prf(byte tag, size_t block_size,
MessageAuthenticationCode& mac,
const byte 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();
}
}
/*
* EAX_Mode Constructor
*/
EAX_Mode::EAX_Mode(BlockCipher* cipher, size_t tag_size) :
m_tag_size(tag_size),
m_cipher(cipher),
m_ctr(new CTR_BE(m_cipher->clone())),
m_cmac(new CMAC(m_cipher->clone()))
{
if(tag_size < 8 || tag_size > m_cmac->output_length())
throw Invalid_Argument(name() + ": Bad tag size " + std::to_string(tag_size));
}
void EAX_Mode::clear()
{
m_cipher.reset();
m_ctr.reset();
m_cmac.reset();
zeroise(m_ad_mac);
zeroise(m_nonce_mac);
}
std::string EAX_Mode::name() const
{
return (m_cipher->name() + "/EAX");
}
size_t EAX_Mode::update_granularity() const
{
return 8 * m_cipher->parallel_bytes();
}
Key_Length_Specification EAX_Mode::key_spec() const
{
return m_cipher->key_spec();
}
/*
* Set the EAX key
*/
void EAX_Mode::key_schedule(const byte key[], size_t length)
{
/*
* 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, length);
m_cmac->set_key(key, length);
m_ad_mac = eax_prf(1, block_size(), *m_cmac, nullptr, 0);
}
/*
* Set the EAX associated data
*/
void EAX_Mode::set_associated_data(const byte ad[], size_t length)
{
m_ad_mac = eax_prf(1, block_size(), *m_cmac, ad, length);
}
secure_vector<byte> EAX_Mode::start(const byte 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[0], m_nonce_mac.size());
for(size_t i = 0; i != block_size() - 1; ++i)
m_cmac->update(0);
m_cmac->update(2);
return secure_vector<byte>();
}
void EAX_Encryption::update(secure_vector<byte>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
const size_t sz = buffer.size() - offset;
byte* buf = &buffer[offset];
m_ctr->cipher(buf, buf, sz);
m_cmac->update(buf, sz);
}
void EAX_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
{
update(buffer, offset);
secure_vector<byte> data_mac = m_cmac->final();
xor_buf(data_mac, m_nonce_mac, data_mac.size());
xor_buf(data_mac, m_ad_mac, data_mac.size());
buffer += std::make_pair(&data_mac[0], tag_size());
}
void EAX_Decryption::update(secure_vector<byte>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
const size_t sz = buffer.size() - offset;
byte* buf = &buffer[offset];
m_cmac->update(buf, sz);
m_ctr->cipher(buf, buf, sz);
}
void EAX_Decryption::finish(secure_vector<byte>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
const size_t sz = buffer.size() - offset;
byte* buf = &buffer[offset];
BOTAN_ASSERT(sz >= tag_size(), "Have the tag as part of final input");
const size_t remaining = sz - tag_size();
if(remaining)
{
m_cmac->update(buf, remaining);
m_ctr->cipher(buf, buf, remaining);
}
const byte* included_tag = &buf[remaining];
secure_vector<byte> mac = m_cmac->final();
mac ^= m_nonce_mac;
mac ^= m_ad_mac;
if(!same_mem(&mac[0], included_tag, tag_size()))
throw Integrity_Failure("EAX tag check failed");
buffer.resize(offset + remaining);
}
}
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