Botan  2.13.0
Crypto and TLS for C++11
mceliece.cpp
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1 /*
2  * (C) Copyright Projet SECRET, INRIA, Rocquencourt
3  * (C) Bhaskar Biswas and Nicolas Sendrier
4  *
5  * (C) 2014 cryptosource GmbH
6  * (C) 2014 Falko Strenzke fstrenzke@cryptosource.de
7  *
8  * Botan is released under the Simplified BSD License (see license.txt)
9  *
10  */
11 
12 #include <botan/internal/mce_internal.h>
13 #include <botan/mceliece.h>
14 #include <botan/internal/code_based_util.h>
15 #include <botan/internal/bit_ops.h>
16 
17 namespace Botan {
18 
19 namespace {
20 
21 secure_vector<uint8_t> concat_vectors(const secure_vector<uint8_t>& a,
22  const secure_vector<uint8_t>& b,
23  size_t dimension,
24  size_t codimension)
25  {
26  secure_vector<uint8_t> x(bit_size_to_byte_size(dimension) + bit_size_to_byte_size(codimension));
27 
28  const size_t final_bits = dimension % 8;
29 
30  if(final_bits == 0)
31  {
32  const size_t dim_bytes = bit_size_to_byte_size(dimension);
33  copy_mem(&x[0], a.data(), dim_bytes);
34  copy_mem(&x[dim_bytes], b.data(), bit_size_to_byte_size(codimension));
35  }
36  else
37  {
38  copy_mem(&x[0], a.data(), (dimension / 8));
39  size_t l = dimension / 8;
40  x[l] = static_cast<uint8_t>(a[l] & ((1 << final_bits) - 1));
41 
42  for(size_t k = 0; k < codimension / 8; ++k)
43  {
44  x[l] ^= static_cast<uint8_t>(b[k] << final_bits);
45  ++l;
46  x[l] = static_cast<uint8_t>(b[k] >> (8 - final_bits));
47  }
48  x[l] ^= static_cast<uint8_t>(b[codimension/8] << final_bits);
49  }
50 
51  return x;
52  }
53 
54 secure_vector<uint8_t> mult_by_pubkey(const secure_vector<uint8_t>& cleartext,
55  std::vector<uint8_t> const& public_matrix,
56  size_t code_length, size_t t)
57  {
58  const size_t ext_deg = ceil_log2(code_length);
59  const size_t codimension = ext_deg * t;
60  const size_t dimension = code_length - codimension;
61  secure_vector<uint8_t> cR(bit_size_to_32bit_size(codimension) * sizeof(uint32_t));
62 
63  const uint8_t* pt = public_matrix.data();
64 
65  for(size_t i = 0; i < dimension / 8; ++i)
66  {
67  for(size_t j = 0; j < 8; ++j)
68  {
69  if(cleartext[i] & (1 << j))
70  {
71  xor_buf(cR.data(), pt, cR.size());
72  }
73  pt += cR.size();
74  }
75  }
76 
77  for(size_t i = 0; i < dimension % 8 ; ++i)
78  {
79  if(cleartext[dimension/8] & (1 << i))
80  {
81  xor_buf(cR.data(), pt, cR.size());
82  }
83  pt += cR.size();
84  }
85 
86  secure_vector<uint8_t> ciphertext = concat_vectors(cleartext, cR, dimension, codimension);
87  ciphertext.resize((code_length+7)/8);
88  return ciphertext;
89  }
90 
91 secure_vector<uint8_t> create_random_error_vector(size_t code_length,
92  size_t error_weight,
93  RandomNumberGenerator& rng)
94  {
95  secure_vector<uint8_t> result((code_length+7)/8);
96 
97  size_t bits_set = 0;
98 
99  while(bits_set < error_weight)
100  {
101  gf2m x = random_code_element(static_cast<uint16_t>(code_length), rng);
102 
103  const size_t byte_pos = x / 8;
104  const size_t bit_pos = x % 8;
105 
106  const uint8_t mask = (1 << bit_pos);
107 
108  if(result[byte_pos] & mask)
109  continue; // already set this bit
110 
111  result[byte_pos] |= mask;
112  bits_set++;
113  }
114 
115  return result;
116  }
117 
118 }
119 
121  secure_vector<uint8_t>& error_mask_out,
122  const secure_vector<uint8_t>& plaintext,
123  const McEliece_PublicKey& key,
125  {
126  const uint16_t code_length = static_cast<uint16_t>(key.get_code_length());
127 
128  secure_vector<uint8_t> error_mask = create_random_error_vector(code_length, key.get_t(), rng);
129 
130  secure_vector<uint8_t> ciphertext = mult_by_pubkey(plaintext, key.get_public_matrix(),
131  key.get_code_length(), key.get_t());
132 
133  ciphertext ^= error_mask;
134 
135  ciphertext_out.swap(ciphertext);
136  error_mask_out.swap(error_mask);
137  }
138 
139 }
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)
Definition: mceliece.cpp:120
size_t get_code_length() const
Definition: mceliece.h:50
size_t bit_size_to_32bit_size(size_t bit_size)
const std::vector< uint8_t > & get_public_matrix() const
Definition: mceliece.h:52
void xor_buf(uint8_t out[], const uint8_t in[], size_t length)
Definition: mem_ops.h:232
uint16_t gf2m
Definition: gf2m_small_m.h:23
void copy_mem(T *out, const T *in, size_t n)
Definition: mem_ops.h:132
size_t bit_size_to_byte_size(size_t bit_size)
Definition: alg_id.cpp:13
gf2m random_code_element(uint16_t code_length, RandomNumberGenerator &rng)
Definition: polyn_gf2m.cpp:71
size_t get_t() const
Definition: mceliece.h:49
std::vector< T, secure_allocator< T > > secure_vector
Definition: secmem.h:65
uint8_t ceil_log2(T x)
Definition: bit_ops.h:119