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/*
* XTS Mode
* (C) 2009,2013 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/xts.h>
#include <botan/loadstor.h>
#include <botan/internal/xor_buf.h>
#include <botan/internal/rounding.h>
namespace Botan {
namespace {
void poly_double_128(byte out[], const byte in[])
{
u64bit X0 = load_le<u64bit>(in, 0);
u64bit X1 = load_le<u64bit>(in, 1);
const bool carry = (X1 >> 63);
X1 = (X1 << 1) | (X0 >> 63);
X0 = (X0 << 1);
if(carry)
X0 ^= 0x87;
store_le(out, X0, X1);
}
void poly_double_64(byte out[], const byte in[])
{
u64bit X = load_le<u64bit>(in, 0);
const bool carry = (X >> 63);
X <<= 1;
if(carry)
X ^= 0x1B;
store_le(X, out);
}
inline void poly_double(byte out[], const byte in[], size_t size)
{
if(size == 8)
poly_double_64(out, in);
else
poly_double_128(out, in);
}
}
XTS_Mode::XTS_Mode(BlockCipher* cipher) : m_cipher(cipher)
{
if(m_cipher->block_size() != 8 && m_cipher->block_size() != 16)
throw std::invalid_argument("Bad cipher for XTS: " + cipher->name());
m_tweak_cipher.reset(m_cipher->clone());
m_tweak.resize(update_granularity());
}
void XTS_Mode::clear()
{
m_cipher->clear();
m_tweak_cipher->clear();
zeroise(m_tweak);
}
std::string XTS_Mode::name() const
{
return cipher().name() + "/XTS";
}
size_t XTS_Mode::update_granularity() const
{
return cipher().parallel_bytes();
}
size_t XTS_Mode::minimum_final_size() const
{
return cipher().block_size() + 1;
}
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 byte 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[0], key_half);
m_tweak_cipher->set_key(&key[key_half], key_half);
}
secure_vector<byte> XTS_Mode::start_raw(const byte nonce[], size_t nonce_len)
{
if(!valid_nonce_length(nonce_len))
throw Invalid_IV_Length(name(), nonce_len);
copy_mem(&m_tweak[0], nonce, nonce_len);
m_tweak_cipher->encrypt(&m_tweak[0]);
update_tweak(0);
return secure_vector<byte>();
}
void XTS_Mode::update_tweak(size_t which)
{
const size_t BS = m_tweak_cipher->block_size();
if(which > 0)
poly_double(&m_tweak[0], &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(&m_tweak[i*BS], &m_tweak[(i-1)*BS], BS);
}
size_t XTS_Encryption::output_length(size_t input_length) const
{
return round_up(input_length, cipher().block_size());
}
void XTS_Encryption::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];
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);
const size_t to_proc_bytes = to_proc * BS;
xor_buf(buf, tweak(), to_proc_bytes);
cipher().encrypt_n(buf, buf, to_proc);
xor_buf(buf, tweak(), to_proc_bytes);
buf += to_proc * BS;
blocks -= to_proc;
update_tweak(to_proc);
}
}
void XTS_Encryption::finish(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];
BOTAN_ASSERT(sz >= minimum_final_size(), "Have sufficient final input");
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<byte> 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
{
// might be less
return input_length;
}
void XTS_Decryption::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];
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);
const size_t to_proc_bytes = to_proc * BS;
xor_buf(buf, tweak(), to_proc_bytes);
cipher().decrypt_n(buf, buf, to_proc);
xor_buf(buf, tweak(), to_proc_bytes);
buf += to_proc * BS;
blocks -= to_proc;
update_tweak(to_proc);
}
}
void XTS_Decryption::finish(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];
BOTAN_ASSERT(sz >= minimum_final_size(), "Have sufficient final input");
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<byte> 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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