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/*
* GMAC
* (C) 2016 Matthias Gierlings, René Korthaus
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/gmac.h>
namespace Botan {
GMAC::GMAC(BlockCipher* cipher)
: GHASH(),
m_aad_buf(),
m_cipher(cipher),
m_initialized(false)
{}
void GMAC::clear()
{
GHASH::clear();
m_H.resize(GCM_BS);
m_H_ad.resize(GCM_BS);
m_ghash.resize(GCM_BS);
m_cipher->clear();
m_aad_buf.clear();
m_initialized = false;
}
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)
{
m_ad_len += size;
// buffer partial blocks till we received a full input block
// or final is called.
m_aad_buf.insert(m_aad_buf.end(), input, input + size);
if(m_aad_buf.size() >= GCM_BS)
{
// process all complete input blocks.
ghash_update(m_ghash,
m_aad_buf.data(),
m_aad_buf.size() - (m_aad_buf.size() % GCM_BS));
// remove all processed blocks from buffer.
m_aad_buf.erase(m_aad_buf.begin(),
m_aad_buf.end() - (m_aad_buf.size() % GCM_BS));
}
}
void GMAC::key_schedule(const uint8_t key[], size_t size)
{
clear();
m_cipher->set_key(key, size);
m_cipher->encrypt(m_H_ad.data(), m_H.data());
}
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
{
ghash_update(y0, nonce, nonce_len);
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());
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).
BOTAN_ASSERT(m_initialized, "GMAC was 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.size() > 0)
{
ghash_update(m_ghash,
m_aad_buf.data(),
m_aad_buf.size());
}
secure_vector<uint8_t> result = GHASH::final();
copy_mem(mac, result.data(), result.size());
clear();
}
MessageAuthenticationCode* GMAC::clone() const
{
return new GMAC(m_cipher->clone());
}
}
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