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/*
* GMAC
* (C) 2016 Matthias Gierlings, René Korthaus
* (C) 2017 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/gmac.h>
#include <botan/ghash.h>
#include <botan/block_cipher.h>
namespace Botan {
GMAC::GMAC(BlockCipher* cipher) :
m_cipher(cipher),
m_ghash(new GHASH),
m_aad_buf(GCM_BS),
m_aad_buf_pos(0),
m_initialized(false)
{
}
void GMAC::clear()
{
m_cipher->clear();
m_ghash->clear();
zeroise(m_aad_buf);
m_aad_buf_pos = 0;
m_initialized = false;
}
GMAC::~GMAC() { /* for unique_ptr */ }
Key_Length_Specification GMAC::key_spec() const
{
return m_cipher->key_spec();
}
std::string GMAC::name() const
{
return "GMAC(" + m_cipher->name() + ")";
}
size_t GMAC::output_length() const
{
return GCM_BS;
}
void GMAC::add_data(const uint8_t input[], size_t size)
{
if(m_aad_buf_pos > 0)
{
const size_t taking = std::min(GCM_BS - m_aad_buf_pos, size);
copy_mem(&m_aad_buf[m_aad_buf_pos], input, taking);
m_aad_buf_pos += taking;
input += taking;
size -= taking;
if(m_aad_buf_pos == GCM_BS)
{
m_ghash->update_associated_data(m_aad_buf.data(), GCM_BS);
m_aad_buf_pos = 0;
}
}
const size_t left_over = size % GCM_BS;
const size_t full_blocks = size - left_over;
m_ghash->update_associated_data(input, full_blocks);
input += full_blocks;
if(left_over > 0)
{
copy_mem(&m_aad_buf[m_aad_buf_pos], input, left_over);
m_aad_buf_pos += left_over;
}
}
void GMAC::key_schedule(const uint8_t key[], size_t size)
{
clear();
m_cipher->set_key(key, size);
secure_vector<uint8_t> H(GCM_BS);
m_cipher->encrypt(H);
m_ghash->set_key(H);
}
void GMAC::start_msg(const uint8_t nonce[], size_t nonce_len)
{
secure_vector<uint8_t> y0(GCM_BS);
if(nonce_len == 12)
{
copy_mem(y0.data(), nonce, nonce_len);
y0[GCM_BS - 1] = 1;
}
else
{
m_ghash->ghash_update(y0, nonce, nonce_len);
m_ghash->add_final_block(y0, 0, nonce_len);
}
secure_vector<uint8_t> m_enc_y0(GCM_BS);
m_cipher->encrypt(y0.data(), m_enc_y0.data());
m_ghash->start(m_enc_y0.data(), m_enc_y0.size());
m_initialized = true;
}
void GMAC::final_result(uint8_t mac[])
{
// This ensures the GMAC computation has been initialized with a fresh
// nonce. The aim of this check is to prevent developers from re-using
// nonces (and potential nonce-reuse attacks).
if(m_initialized == false)
throw Invalid_State("GMAC was not used with a fresh nonce");
// process the rest of the aad buffer. Even if it is a partial block only
// ghash_update will process it properly.
if(m_aad_buf_pos > 0)
{
m_ghash->update_associated_data(m_aad_buf.data(), m_aad_buf_pos);
}
secure_vector<uint8_t> result = m_ghash->final();
copy_mem(mac, result.data(), result.size());
clear();
}
MessageAuthenticationCode* GMAC::clone() const
{
return new GMAC(m_cipher->clone());
}
}
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