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/**
* (C) Copyright Projet SECRET, INRIA, Rocquencourt
* (C) Bhaskar Biswas and Nicolas Sendrier
*
* (C) 2014 cryptosource GmbH
* (C) 2014 Falko Strenzke fstrenzke@cryptosource.de
*
* Botan is released under the Simplified BSD License (see license.txt)
*
*/
#include <botan/mceliece.h>
#include <botan/mceliece_key.h>
#include <botan/internal/code_based_key_gen.h>
#include <botan/polyn_gf2m.h>
#include <botan/code_based_util.h>
#include <botan/goppa_code.h>
#include <botan/internal/bit_ops.h>
#include <botan/internal/xor_buf.h>
namespace Botan {
namespace {
void concat_vectors(byte* x, const byte* a, const byte* b, u32bit dimension, u32bit codimension)
{
if(dimension % 8 == 0)
{
const size_t dim_bytes = bit_size_to_byte_size(dimension);
copy_mem(x, a, dim_bytes);
copy_mem(x + dim_bytes, b, bit_size_to_byte_size(codimension));
}
else
{
u32bit i, j, k, l;
i = dimension - 8 * (dimension/ 8);
j = 8 - i;
l = dimension / 8;
copy_mem(x, a, 1 * (dimension / 8));
x[l] = static_cast<byte>(a[l] & ((1 << i) - 1));
for(k = 0; k < codimension / 8; ++k)
{
x[l] ^= static_cast<byte>(b[k] << i);
++l;
x[l] = static_cast<byte>(b[k] >> j);
}
x[l] ^= static_cast<byte>(b[k] << i);
}
}
std::vector<byte> mult_by_pubkey(const byte *cleartext,
std::vector<byte> const& public_matrix,
u32bit code_length, u32bit t)
{
std::vector<byte> ciphertext(code_length);
u32bit i, j;
u32bit ext_deg = ceil_log2(code_length);
u32bit codimension = ext_deg * t;
u32bit dimension = code_length - codimension;
std::vector<byte> cR(bit_size_to_32bit_size(codimension)* sizeof(u32bit));
const byte* pt = &public_matrix[0];
for(i = 0; i < dimension / 8; ++i)
{
for(j = 0; j < 8; ++j)
{
if(cleartext[i] & (1 << j))
{
xor_buf(&cR[0], pt, cR.size());
}
pt += bit_size_to_32bit_size(codimension) * sizeof(u32bit);
}
}
for(j = 0; j < dimension % 8 ; ++j)
{
if(cleartext[i] & (1 << j))
{
xor_buf(&cR[0], pt, bit_size_to_byte_size(codimension));
}
pt += bit_size_to_32bit_size(codimension) * sizeof(u32bit);
}
concat_vectors( &ciphertext[0], cleartext, &cR[0], dimension, codimension);
return ciphertext;
}
}
secure_vector<gf2m> create_random_error_positions(unsigned code_length,
unsigned error_weight,
RandomNumberGenerator& rng)
{
secure_vector<gf2m> result(error_weight);
gf2m i;
for(i = 0; i < result.size(); i++)
{
unsigned j;
char try_again = 0;
do
{
try_again = 0;
gf2m new_pos = random_code_element(code_length, rng);
for(j = 0; j < i; j++)
{
if(new_pos == result[j])
{
try_again = 1;
break;
}
}
result[i] = new_pos;
} while(try_again);
}
return result;
}
McEliece_Private_Operation::McEliece_Private_Operation(const McEliece_PrivateKey& private_key)
:m_priv_key(private_key)
{
}
secure_vector<byte> McEliece_Private_Operation::decrypt(const byte msg[], size_t msg_len)
{
secure_vector<gf2m> err_pos;
secure_vector<byte> plaintext = mceliece_decrypt(
err_pos,
msg, msg_len,
m_priv_key
);
return mceliece_message_parts(err_pos, plaintext, m_priv_key.get_code_length()).get_concat();
}
McEliece_Public_Operation::McEliece_Public_Operation(const McEliece_PublicKey& public_key, u32bit the_code_length)
:m_pub_key(public_key),
m_code_length(the_code_length)
{}
secure_vector<byte> McEliece_Public_Operation::encrypt(const byte msg[], size_t msg_len, RandomNumberGenerator&)
{
mceliece_message_parts parts(msg, msg_len, m_pub_key.get_code_length());
secure_vector<gf2m> err_pos = parts.get_error_positions();
secure_vector<byte> message_word = parts.get_message_word();
secure_vector<byte> ciphertext((m_pub_key.get_code_length()+7)/8);
std::vector<byte> ciphertext_tmp = mceliece_encrypt( message_word, m_pub_key.get_public_matrix(), err_pos, m_code_length);
copy_mem(&ciphertext[0], &ciphertext_tmp[0], ciphertext.size());
return ciphertext;
}
std::vector<byte> mceliece_encrypt(const secure_vector<byte> & cleartext,
std::vector<byte> const& public_matrix,
const secure_vector<gf2m> & err_pos,
u32bit code_length)
{
std::vector<byte> ciphertext = mult_by_pubkey(&cleartext[0], public_matrix, code_length, err_pos.size());
// flip t error positions
for(size_t i = 0; i < err_pos.size(); ++i)
{
ciphertext[err_pos[i] / 8] ^= (1 << (err_pos[i] % 8));
}
return ciphertext;
}
}
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