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/*
* SIV Mode Encryption
* (C) 2013 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/siv.h>
#include <botan/cmac.h>
#include <botan/ctr.h>
#include <botan/parsing.h>
#include <botan/internal/xor_buf.h>
#include <algorithm>
namespace Botan {
SIV_Mode::SIV_Mode(BlockCipher* cipher) :
m_name(cipher->name() + "/SIV"),
m_ctr(new CTR_BE(cipher->clone())),
m_cmac(new CMAC(cipher))
{
}
void SIV_Mode::clear()
{
m_ctr.reset();
m_nonce.clear();
m_msg_buf.clear();
m_ad_macs.clear();
}
std::string SIV_Mode::name() const
{
return m_name;
}
bool SIV_Mode::valid_nonce_length(size_t) const
{
return true;
}
size_t SIV_Mode::update_granularity() const
{
/*
This value does not particularly matter as regardless SIV_Mode::update
buffers all input, so in theory this could be 1. However as for instance
Transformation_Filter creates update_granularity() byte buffers, use a
somewhat large size to avoid bouncing on a tiny buffer.
*/
return 128;
}
Key_Length_Specification SIV_Mode::key_spec() const
{
return m_cmac->key_spec().multiple(2);
}
void SIV_Mode::key_schedule(const byte key[], size_t length)
{
const size_t keylen = length / 2;
m_cmac->set_key(key, keylen);
m_ctr->set_key(key + keylen, keylen);
m_ad_macs.clear();
}
void SIV_Mode::set_associated_data_n(size_t n, const byte ad[], size_t length)
{
if(n >= m_ad_macs.size())
m_ad_macs.resize(n+1);
m_ad_macs[n] = m_cmac->process(ad, length);
}
secure_vector<byte> SIV_Mode::start(const byte nonce[], size_t nonce_len)
{
if(!valid_nonce_length(nonce_len))
throw Invalid_IV_Length(name(), nonce_len);
if(nonce_len)
m_nonce = m_cmac->process(nonce, nonce_len);
else
m_nonce.clear();
m_msg_buf.clear();
return secure_vector<byte>();
}
void SIV_Mode::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_msg_buf.insert(m_msg_buf.end(), buf, buf + sz);
buffer.resize(offset); // truncate msg
}
secure_vector<byte> SIV_Mode::S2V(const byte* text, size_t text_len)
{
const byte zero[16] = { 0 };
secure_vector<byte> V = cmac().process(zero, 16);
for(size_t i = 0; i != m_ad_macs.size(); ++i)
{
V = CMAC::poly_double(V, 0x87);
V ^= m_ad_macs[i];
}
if(m_nonce.size())
{
V = CMAC::poly_double(V, 0x87);
V ^= m_nonce;
}
if(text_len < 16)
{
V = CMAC::poly_double(V, 0x87);
xor_buf(&V[0], text, text_len);
V[text_len] ^= 0x80;
return cmac().process(V);
}
cmac().update(text, text_len - 16);
xor_buf(&V[0], &text[text_len - 16], 16);
cmac().update(V);
return cmac().final();
}
void SIV_Mode::set_ctr_iv(secure_vector<byte> V)
{
V[8] &= 0x7F;
V[12] &= 0x7F;
ctr().set_iv(&V[0], V.size());
}
void SIV_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
buffer.insert(buffer.begin() + offset, msg_buf().begin(), msg_buf().end());
secure_vector<byte> V = S2V(&buffer[offset], buffer.size() - offset);
buffer.insert(buffer.begin() + offset, V.begin(), V.end());
set_ctr_iv(V);
ctr().cipher1(&buffer[offset + V.size()], buffer.size() - offset - V.size());
}
void SIV_Decryption::finish(secure_vector<byte>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
buffer.insert(buffer.begin() + offset, msg_buf().begin(), msg_buf().end());
const size_t sz = buffer.size() - offset;
BOTAN_ASSERT(sz >= tag_size(), "We have the tag");
secure_vector<byte> V(&buffer[offset], &buffer[offset + 16]);
set_ctr_iv(V);
ctr().cipher(&buffer[offset + V.size()],
&buffer[offset],
buffer.size() - offset - V.size());
secure_vector<byte> T = S2V(&buffer[offset], buffer.size() - offset - V.size());
if(T != V)
throw Integrity_Failure("SIV tag check failed");
buffer.resize(buffer.size() - tag_size());
}
}
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