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/*
* GCM Mode Encryption
* (C) 2013,2015 Jack Lloyd
* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/gcm.h>
#include <botan/ghash.h>
#include <botan/block_cipher.h>
#include <botan/ctr.h>
namespace Botan {
/*
* GCM_Mode Constructor
*/
GCM_Mode::GCM_Mode(BlockCipher* cipher, size_t tag_size) :
m_tag_size(tag_size),
m_cipher_name(cipher->name())
{
if(cipher->block_size() != GCM_BS)
throw Invalid_Argument("Invalid block cipher for GCM");
m_ghash.reset(new GHASH);
m_ctr.reset(new CTR_BE(cipher, 4)); // CTR_BE takes ownership of cipher
/* We allow any of the values 128, 120, 112, 104, or 96 bits as a tag size */
/* 64 bit tag is still supported but deprecated and will be removed in the future */
if(m_tag_size != 8 && (m_tag_size < 12 || m_tag_size > 16))
throw Invalid_Argument(name() + ": Bad tag size " + std::to_string(m_tag_size));
}
GCM_Mode::~GCM_Mode() { /* for unique_ptr */ }
void GCM_Mode::clear()
{
m_ctr->clear();
m_ghash->clear();
reset();
}
void GCM_Mode::reset()
{
m_ghash->reset();
}
std::string GCM_Mode::name() const
{
return (m_cipher_name + "/GCM(" + std::to_string(tag_size()) + ")");
}
std::string GCM_Mode::provider() const
{
return m_ghash->provider();
}
size_t GCM_Mode::update_granularity() const
{
return GCM_BS;
}
bool GCM_Mode::valid_nonce_length(size_t len) const
{
// GCM does not support empty nonces
return (len > 0);
}
Key_Length_Specification GCM_Mode::key_spec() const
{
return m_ctr->key_spec();
}
void GCM_Mode::key_schedule(const uint8_t key[], size_t keylen)
{
m_ctr->set_key(key, keylen);
const std::vector<uint8_t> zeros(GCM_BS);
m_ctr->set_iv(zeros.data(), zeros.size());
secure_vector<uint8_t> H(GCM_BS);
m_ctr->encipher(H);
m_ghash->set_key(H);
}
void GCM_Mode::set_associated_data(const uint8_t ad[], size_t ad_len)
{
m_ghash->set_associated_data(ad, ad_len);
}
void GCM_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)
{
if(!valid_nonce_length(nonce_len))
throw Invalid_IV_Length(name(), nonce_len);
secure_vector<uint8_t> y0(GCM_BS);
if(nonce_len == 12)
{
copy_mem(y0.data(), nonce, nonce_len);
y0[15] = 1;
}
else
{
y0 = m_ghash->nonce_hash(nonce, nonce_len);
}
m_ctr->set_iv(y0.data(), y0.size());
zeroise(y0);
m_ctr->encipher(y0);
m_ghash->start(y0.data(), y0.size());
}
size_t GCM_Encryption::process(uint8_t buf[], size_t sz)
{
BOTAN_ARG_CHECK(sz % update_granularity() == 0, "Invalid buffer size");
m_ctr->cipher(buf, buf, sz);
m_ghash->update(buf, sz);
return sz;
}
void GCM_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
{
BOTAN_ARG_CHECK(offset <= buffer.size(), "Invalid offset");
const size_t sz = buffer.size() - offset;
uint8_t* buf = buffer.data() + offset;
m_ctr->cipher(buf, buf, sz);
m_ghash->update(buf, sz);
auto mac = m_ghash->final();
buffer += std::make_pair(mac.data(), tag_size());
}
size_t GCM_Decryption::process(uint8_t buf[], size_t sz)
{
BOTAN_ARG_CHECK(sz % update_granularity() == 0, "Invalid buffer size");
m_ghash->update(buf, sz);
m_ctr->cipher(buf, buf, sz);
return sz;
}
void GCM_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
{
BOTAN_ARG_CHECK(offset <= buffer.size(), "Invalid offset");
const size_t sz = buffer.size() - offset;
uint8_t* buf = buffer.data() + offset;
if(sz < tag_size())
throw Exception("Insufficient input for GCM decryption, tag missing");
const size_t remaining = sz - tag_size();
// handle any final input before the tag
if(remaining)
{
m_ghash->update(buf, remaining);
m_ctr->cipher(buf, buf, remaining);
}
auto mac = m_ghash->final();
const uint8_t* included_tag = &buffer[remaining+offset];
if(!constant_time_compare(mac.data(), included_tag, tag_size()))
throw Integrity_Failure("GCM tag check failed");
buffer.resize(offset + remaining);
}
}
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