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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/internal/mce_internal.h>
#include <botan/mceliece.h>
#include <botan/internal/code_based_util.h>
#include <botan/internal/bit_ops.h>
#include <set>
namespace Botan {
namespace {
secure_vector<byte> concat_vectors(const secure_vector<byte>& a, const secure_vector<byte>& b,
u32bit dimension, u32bit codimension)
{
secure_vector<byte> x(bit_size_to_byte_size(dimension) + bit_size_to_byte_size(codimension));
const size_t final_bits = dimension % 8;
if(final_bits == 0)
{
const size_t dim_bytes = bit_size_to_byte_size(dimension);
copy_mem(&x[0], a.data(), dim_bytes);
copy_mem(&x[dim_bytes], b.data(), bit_size_to_byte_size(codimension));
}
else
{
copy_mem(&x[0], a.data(), (dimension / 8));
u32bit l = dimension / 8;
x[l] = static_cast<byte>(a[l] & ((1 << final_bits) - 1));
for(u32bit k = 0; k < codimension / 8; ++k)
{
x[l] ^= static_cast<byte>(b[k] << final_bits);
++l;
x[l] = static_cast<byte>(b[k] >> (8 - final_bits));
}
x[l] ^= static_cast<byte>(b[codimension/8] << final_bits);
}
return x;
}
secure_vector<byte> mult_by_pubkey(const secure_vector<byte>& cleartext,
std::vector<byte> const& public_matrix,
u32bit code_length, u32bit t)
{
const u32bit ext_deg = ceil_log2(code_length);
const u32bit codimension = ext_deg * t;
const u32bit dimension = code_length - codimension;
secure_vector<byte> cR(bit_size_to_32bit_size(codimension) * sizeof(u32bit));
const byte* pt = public_matrix.data();
for(size_t i = 0; i < dimension / 8; ++i)
{
for(size_t j = 0; j < 8; ++j)
{
if(cleartext[i] & (1 << j))
{
xor_buf(cR.data(), pt, cR.size());
}
pt += cR.size();
}
}
for(size_t i = 0; i < dimension % 8 ; ++i)
{
if(cleartext[dimension/8] & (1 << i))
{
xor_buf(cR.data(), pt, cR.size());
}
pt += cR.size();
}
secure_vector<byte> ciphertext = concat_vectors(cleartext, cR, dimension, codimension);
ciphertext.resize((code_length+7)/8);
return ciphertext;
}
secure_vector<byte> create_random_error_vector(unsigned code_length,
unsigned error_weight,
RandomNumberGenerator& rng)
{
secure_vector<byte> result((code_length+7)/8);
size_t bits_set = 0;
while(bits_set < error_weight)
{
gf2m x = random_code_element(code_length, rng);
const size_t byte_pos = x / 8, bit_pos = x % 8;
const byte mask = (1 << bit_pos);
if(result[byte_pos] & mask)
continue; // already set this bit
result[byte_pos] |= mask;
bits_set++;
}
return result;
}
}
void mceliece_encrypt(secure_vector<byte>& ciphertext_out,
secure_vector<byte>& error_mask_out,
const secure_vector<byte>& plaintext,
const McEliece_PublicKey& key,
RandomNumberGenerator& rng)
{
secure_vector<byte> error_mask = create_random_error_vector(key.get_code_length(), key.get_t(), rng);
secure_vector<byte> ciphertext = mult_by_pubkey(plaintext, key.get_public_matrix(),
key.get_code_length(), key.get_t());
ciphertext ^= error_mask;
ciphertext_out.swap(ciphertext);
error_mask_out.swap(error_mask);
}
}
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