1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
|
/*
* (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>
namespace Botan {
namespace {
secure_vector<uint8_t> concat_vectors(const secure_vector<uint8_t>& a,
const secure_vector<uint8_t>& b,
size_t dimension,
size_t codimension)
{
secure_vector<uint8_t> 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));
size_t l = dimension / 8;
x[l] = static_cast<uint8_t>(a[l] & ((1 << final_bits) - 1));
for(size_t k = 0; k < codimension / 8; ++k)
{
x[l] ^= static_cast<uint8_t>(b[k] << final_bits);
++l;
x[l] = static_cast<uint8_t>(b[k] >> (8 - final_bits));
}
x[l] ^= static_cast<uint8_t>(b[codimension/8] << final_bits);
}
return x;
}
secure_vector<uint8_t> mult_by_pubkey(const secure_vector<uint8_t>& cleartext,
std::vector<uint8_t> const& public_matrix,
size_t code_length, size_t t)
{
const size_t ext_deg = ceil_log2(code_length);
const size_t codimension = ext_deg * t;
const size_t dimension = code_length - codimension;
secure_vector<uint8_t> cR(bit_size_to_32bit_size(codimension) * sizeof(uint32_t));
const uint8_t* 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<uint8_t> ciphertext = concat_vectors(cleartext, cR, dimension, codimension);
ciphertext.resize((code_length+7)/8);
return ciphertext;
}
secure_vector<uint8_t> create_random_error_vector(size_t code_length,
size_t error_weight,
RandomNumberGenerator& rng)
{
secure_vector<uint8_t> result((code_length+7)/8);
size_t bits_set = 0;
while(bits_set < error_weight)
{
gf2m x = random_code_element(static_cast<uint16_t>(code_length), rng);
const size_t byte_pos = x / 8;
const size_t bit_pos = x % 8;
const uint8_t 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<uint8_t>& ciphertext_out,
secure_vector<uint8_t>& error_mask_out,
const secure_vector<uint8_t>& plaintext,
const McEliece_PublicKey& key,
RandomNumberGenerator& rng)
{
const uint16_t code_length = static_cast<uint16_t>(key.get_code_length());
secure_vector<uint8_t> error_mask = create_random_error_vector(code_length, key.get_t(), rng);
secure_vector<uint8_t> 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);
}
}
|
