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/*
* XTS Mode
* (C) 2009 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/xts.h>
#include <botan/xor_buf.h>
#include <algorithm>
#include <stdexcept>
namespace Botan {
namespace {
void poly_double(byte tweak[], u32bit size)
{
const byte polynomial = 0x87; // for 128 bit ciphers
byte carry = 0;
for(u32bit i = 0; i != size; ++i)
{
byte carry2 = (tweak[i] >> 7);
tweak[i] = (tweak[i] << 1) | carry;
carry = carry2;
}
if(carry)
tweak[0] ^= polynomial;
}
}
/*
* XTS_Encryption constructor
*/
XTS_Encryption::XTS_Encryption(BlockCipher* ciph) : cipher(ciph)
{
if(cipher->BLOCK_SIZE != 16)
throw std::invalid_argument("Bad cipher for XTS: " + cipher->name());
cipher2 = cipher->clone();
tweak.create(cipher->BLOCK_SIZE);
buffer.create(2 * cipher->BLOCK_SIZE);
position = 0;
}
/*
* XTS_Encryption constructor
*/
XTS_Encryption::XTS_Encryption(BlockCipher* ciph,
const SymmetricKey& key,
const InitializationVector& iv) : cipher(ciph)
{
if(cipher->BLOCK_SIZE != 16)
throw std::invalid_argument("Bad cipher for XTS: " + cipher->name());
cipher2 = cipher->clone();
tweak.create(cipher->BLOCK_SIZE);
buffer.create(2 * cipher->BLOCK_SIZE);
position = 0;
set_key(key);
set_iv(iv);
}
/*
* Return the name
*/
std::string XTS_Encryption::name() const
{
return (cipher->name() + "/XTS");
}
/*
* Set new tweak
*/
void XTS_Encryption::set_iv(const InitializationVector& iv)
{
if(iv.length() != tweak.size())
throw Invalid_IV_Length(name(), iv.length());
tweak = iv.bits_of();
cipher2->encrypt(tweak);
}
void XTS_Encryption::set_key(const SymmetricKey& key)
{
u32bit key_half = key.length() / 2;
if(key.length() % 2 == 1 || !cipher->valid_keylength(key_half))
throw Invalid_Key_Length(name(), key.length());
cipher->set_key(key.begin(), key_half);
cipher2->set_key(key.begin() + key_half, key_half);
}
void XTS_Encryption::encrypt(const byte block[])
{
/*
* We can always use the first 16 bytes of buffer as temp space,
* since either the input block is buffer (in which case this is
* just buffer ^= tweak) or it not, in which case we already read
* and used the data there and are processing new input. Kind of
* subtle/nasty, but saves allocating a distinct temp buf.
*/
xor_buf(buffer, block, tweak, cipher->BLOCK_SIZE);
cipher->encrypt(buffer);
xor_buf(buffer, tweak, cipher->BLOCK_SIZE);
poly_double(tweak, cipher->BLOCK_SIZE);
send(buffer, cipher->BLOCK_SIZE);
}
/*
* Encrypt in XTS mode
*/
void XTS_Encryption::write(const byte input[], u32bit length)
{
const u32bit BLOCK_SIZE = cipher->BLOCK_SIZE;
u32bit copied = std::min(buffer.size() - position, length);
buffer.copy(position, input, copied);
length -= copied;
input += copied;
position += copied;
if(length == 0) return;
encrypt(buffer);
if(length > BLOCK_SIZE)
{
encrypt(buffer + BLOCK_SIZE);
while(length > buffer.size())
{
encrypt(input);
length -= BLOCK_SIZE;
input += BLOCK_SIZE;
}
position = 0;
}
else
{
copy_mem(buffer.begin(), buffer + BLOCK_SIZE, BLOCK_SIZE);
position = BLOCK_SIZE;
}
buffer.copy(position, input, length);
position += length;
}
/*
* Finish encrypting in XTS mode
*/
void XTS_Encryption::end_msg()
{
const u32bit BLOCK_SIZE = cipher->BLOCK_SIZE;
if(position < BLOCK_SIZE)
throw Exception("XTS_Encryption: insufficient data to encrypt");
else if(position == BLOCK_SIZE)
{
encrypt(buffer);
}
else if(position == 2*BLOCK_SIZE)
{
encrypt(buffer);
encrypt(buffer + BLOCK_SIZE);
}
else
{ // steal ciphertext
xor_buf(buffer, tweak, cipher->BLOCK_SIZE);
cipher->encrypt(buffer);
xor_buf(buffer, tweak, cipher->BLOCK_SIZE);
poly_double(tweak, cipher->BLOCK_SIZE);
for(u32bit i = 0; i != position - cipher->BLOCK_SIZE; ++i)
std::swap(buffer[i], buffer[i + cipher->BLOCK_SIZE]);
xor_buf(buffer, tweak, cipher->BLOCK_SIZE);
cipher->encrypt(buffer);
xor_buf(buffer, tweak, cipher->BLOCK_SIZE);
send(buffer, position);
}
position = 0;
}
/*
* XTS_Decryption constructor
*/
XTS_Decryption::XTS_Decryption(BlockCipher* ciph)
{
cipher = ciph;
cipher2 = ciph->clone();
tweak.create(cipher->BLOCK_SIZE);
buffer.create(2 * cipher->BLOCK_SIZE);
position = 0;
}
/*
* XTS_Decryption constructor
*/
XTS_Decryption::XTS_Decryption(BlockCipher* ciph,
const SymmetricKey& key,
const InitializationVector& iv)
{
cipher = ciph;
cipher2 = ciph->clone();
tweak.create(cipher->BLOCK_SIZE);
buffer.create(2 * cipher->BLOCK_SIZE);
position = 0;
set_key(key);
set_iv(iv);
}
/*
* Return the name
*/
std::string XTS_Decryption::name() const
{
return (cipher->name() + "/XTS");
}
/*
* Set new tweak
*/
void XTS_Decryption::set_iv(const InitializationVector& iv)
{
if(iv.length() != tweak.size())
throw Invalid_IV_Length(name(), iv.length());
tweak = iv.bits_of();
cipher2->encrypt(tweak);
}
void XTS_Decryption::set_key(const SymmetricKey& key)
{
u32bit key_half = key.length() / 2;
if(key.length() % 2 == 1 || !cipher->valid_keylength(key_half))
throw Invalid_Key_Length(name(), key.length());
cipher->set_key(key.begin(), key_half);
cipher2->set_key(key.begin() + key_half, key_half);
}
/*
* Decrypt a block
*/
void XTS_Decryption::decrypt(const byte block[])
{
xor_buf(buffer, block, tweak, cipher->BLOCK_SIZE);
cipher->decrypt(buffer);
xor_buf(buffer, tweak, cipher->BLOCK_SIZE);
poly_double(tweak, cipher->BLOCK_SIZE);
send(buffer, cipher->BLOCK_SIZE);
}
/*
* Decrypt in XTS mode
*/
void XTS_Decryption::write(const byte input[], u32bit length)
{
const u32bit BLOCK_SIZE = cipher->BLOCK_SIZE;
u32bit copied = std::min(buffer.size() - position, length);
buffer.copy(position, input, copied);
length -= copied;
input += copied;
position += copied;
if(length == 0) return;
decrypt(buffer);
if(length > BLOCK_SIZE)
{
decrypt(buffer + BLOCK_SIZE);
while(length > 2*BLOCK_SIZE)
{
decrypt(input);
length -= BLOCK_SIZE;
input += BLOCK_SIZE;
}
position = 0;
}
else
{
copy_mem(buffer.begin(), buffer + BLOCK_SIZE, BLOCK_SIZE);
position = BLOCK_SIZE;
}
buffer.copy(position, input, length);
position += length;
}
/*
* Finish decrypting in XTS mode
*/
void XTS_Decryption::end_msg()
{
const u32bit BLOCK_SIZE = cipher->BLOCK_SIZE;
if(position < BLOCK_SIZE)
throw Exception("XTS_Decryption: insufficient data to decrypt");
else if(position == BLOCK_SIZE)
{
decrypt(buffer);
}
else if(position == 2*BLOCK_SIZE)
{
decrypt(buffer);
decrypt(buffer + BLOCK_SIZE);
}
else
{
SecureVector<byte> tweak2 = tweak;
poly_double(tweak2, cipher->BLOCK_SIZE);
xor_buf(buffer, tweak2, cipher->BLOCK_SIZE);
cipher->decrypt(buffer);
xor_buf(buffer, tweak2, cipher->BLOCK_SIZE);
for(u32bit i = 0; i != position - cipher->BLOCK_SIZE; ++i)
std::swap(buffer[i], buffer[i + cipher->BLOCK_SIZE]);
xor_buf(buffer, tweak, cipher->BLOCK_SIZE);
cipher->decrypt(buffer);
xor_buf(buffer, tweak, cipher->BLOCK_SIZE);
send(buffer, position);
}
position = 0;
}
}
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