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/*
* XTS Mode
* (C) 2009,2013 Jack Lloyd
* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/xts.h>
#include <botan/internal/poly_dbl.h>
namespace Botan {
XTS_Mode::XTS_Mode(BlockCipher* cipher) :
m_cipher(cipher),
m_cipher_block_size(m_cipher->block_size()),
m_cipher_parallelism(m_cipher->parallel_bytes())
{
if(poly_double_supported_size(m_cipher_block_size) == false)
{
throw Invalid_Argument("Cannot use " + cipher->name() + " with XTS");
}
m_tweak_cipher.reset(m_cipher->clone());
}
void XTS_Mode::clear()
{
m_cipher->clear();
m_tweak_cipher->clear();
reset();
}
void XTS_Mode::reset()
{
m_tweak.clear();
}
std::string XTS_Mode::name() const
{
return cipher().name() + "/XTS";
}
size_t XTS_Mode::minimum_final_size() const
{
return cipher_block_size();
}
Key_Length_Specification XTS_Mode::key_spec() const
{
return cipher().key_spec().multiple(2);
}
size_t XTS_Mode::default_nonce_length() const
{
return cipher_block_size();
}
bool XTS_Mode::valid_nonce_length(size_t n) const
{
return cipher_block_size() == n;
}
void XTS_Mode::key_schedule(const uint8_t key[], size_t length)
{
const size_t key_half = length / 2;
if(length % 2 == 1 || !m_cipher->valid_keylength(key_half))
throw Invalid_Key_Length(name(), length);
m_cipher->set_key(key, key_half);
m_tweak_cipher->set_key(&key[key_half], key_half);
}
void XTS_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)
{
if(!valid_nonce_length(nonce_len))
throw Invalid_IV_Length(name(), nonce_len);
m_tweak.resize(update_granularity());
copy_mem(m_tweak.data(), nonce, nonce_len);
m_tweak_cipher->encrypt(m_tweak.data());
update_tweak(0);
}
void XTS_Mode::update_tweak(size_t which)
{
const size_t BS = m_tweak_cipher->block_size();
if(which > 0)
poly_double_n_le(m_tweak.data(), &m_tweak[(which-1)*BS], BS);
const size_t blocks_in_tweak = update_granularity() / BS;
for(size_t i = 1; i < blocks_in_tweak; ++i)
poly_double_n_le(&m_tweak[i*BS], &m_tweak[(i-1)*BS], BS);
}
size_t XTS_Encryption::output_length(size_t input_length) const
{
return input_length;
}
size_t XTS_Encryption::process(uint8_t buf[], size_t sz)
{
BOTAN_STATE_CHECK(tweak_set());
const size_t BS = cipher_block_size();
BOTAN_ASSERT(sz % BS == 0, "Input is full blocks");
size_t blocks = sz / BS;
const size_t blocks_in_tweak = update_granularity() / BS;
while(blocks)
{
const size_t to_proc = std::min(blocks, blocks_in_tweak);
cipher().encrypt_n_xex(buf, tweak(), to_proc);
buf += to_proc * BS;
blocks -= to_proc;
update_tweak(to_proc);
}
return sz;
}
void XTS_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
const size_t sz = buffer.size() - offset;
uint8_t* buf = buffer.data() + offset;
BOTAN_ASSERT(sz >= minimum_final_size(), "Have sufficient final input in XTS encrypt");
const size_t BS = cipher_block_size();
if(sz % BS == 0)
{
update(buffer, offset);
}
else
{
// steal ciphertext
const size_t full_blocks = ((sz / BS) - 1) * BS;
const size_t final_bytes = sz - full_blocks;
BOTAN_ASSERT(final_bytes > BS && final_bytes < 2*BS, "Left over size in expected range");
secure_vector<uint8_t> last(buf + full_blocks, buf + full_blocks + final_bytes);
buffer.resize(full_blocks + offset);
update(buffer, offset);
xor_buf(last, tweak(), BS);
cipher().encrypt(last);
xor_buf(last, tweak(), BS);
for(size_t i = 0; i != final_bytes - BS; ++i)
{
last[i] ^= last[i + BS];
last[i + BS] ^= last[i];
last[i] ^= last[i + BS];
}
xor_buf(last, tweak() + BS, BS);
cipher().encrypt(last);
xor_buf(last, tweak() + BS, BS);
buffer += last;
}
}
size_t XTS_Decryption::output_length(size_t input_length) const
{
return input_length;
}
size_t XTS_Decryption::process(uint8_t buf[], size_t sz)
{
BOTAN_STATE_CHECK(tweak_set());
const size_t BS = cipher_block_size();
BOTAN_ASSERT(sz % BS == 0, "Input is full blocks");
size_t blocks = sz / BS;
const size_t blocks_in_tweak = update_granularity() / BS;
while(blocks)
{
const size_t to_proc = std::min(blocks, blocks_in_tweak);
cipher().decrypt_n_xex(buf, tweak(), to_proc);
buf += to_proc * BS;
blocks -= to_proc;
update_tweak(to_proc);
}
return sz;
}
void XTS_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
const size_t sz = buffer.size() - offset;
uint8_t* buf = buffer.data() + offset;
BOTAN_ASSERT(sz >= minimum_final_size(), "Have sufficient final input in XTS decrypt");
const size_t BS = cipher_block_size();
if(sz % BS == 0)
{
update(buffer, offset);
}
else
{
// steal ciphertext
const size_t full_blocks = ((sz / BS) - 1) * BS;
const size_t final_bytes = sz - full_blocks;
BOTAN_ASSERT(final_bytes > BS && final_bytes < 2*BS, "Left over size in expected range");
secure_vector<uint8_t> last(buf + full_blocks, buf + full_blocks + final_bytes);
buffer.resize(full_blocks + offset);
update(buffer, offset);
xor_buf(last, tweak() + BS, BS);
cipher().decrypt(last);
xor_buf(last, tweak() + BS, BS);
for(size_t i = 0; i != final_bytes - BS; ++i)
{
last[i] ^= last[i + BS];
last[i + BS] ^= last[i];
last[i] ^= last[i + BS];
}
xor_buf(last, tweak(), BS);
cipher().decrypt(last);
xor_buf(last, tweak(), BS);
buffer += last;
}
}
}
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