Botan  2.13.0
Crypto and TLS for C++11
goppa_code.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/internal/code_based_util.h>
14 
15 namespace Botan {
16 
17 namespace {
18 
19 void matrix_arr_mul(std::vector<uint32_t> matrix,
20  size_t numo_rows,
21  size_t words_per_row,
22  const uint8_t input_vec[],
23  uint32_t output_vec[],
24  size_t output_vec_len)
25  {
26  for(size_t j = 0; j < numo_rows; j++)
27  {
28  if((input_vec[j / 8] >> (j % 8)) & 1)
29  {
30  for(size_t i = 0; i < output_vec_len; i++)
31  {
32  output_vec[i] ^= matrix[j * (words_per_row) + i];
33  }
34  }
35  }
36  }
37 
38 /**
39 * returns the error vector to the syndrome
40 */
41 secure_vector<gf2m> goppa_decode(const polyn_gf2m & syndrom_polyn,
42  const polyn_gf2m & g,
43  const std::vector<polyn_gf2m> & sqrtmod,
44  const std::vector<gf2m> & Linv)
45  {
46  const size_t code_length = Linv.size();
47  gf2m a;
48  uint32_t t = g.get_degree();
49 
50  std::shared_ptr<GF2m_Field> sp_field = g.get_sp_field();
51 
52  std::pair<polyn_gf2m, polyn_gf2m> h_aux = polyn_gf2m::eea_with_coefficients( syndrom_polyn, g, 1);
53  polyn_gf2m & h = h_aux.first;
54  polyn_gf2m & aux = h_aux.second;
55  a = sp_field->gf_inv(aux.get_coef(0));
56  gf2m log_a = sp_field->gf_log(a);
57  for(int i = 0; i <= h.get_degree(); ++i)
58  {
59  h.set_coef(i,sp_field->gf_mul_zrz(log_a,h.get_coef(i)));
60  }
61 
62  // compute h(z) += z
63  h.add_to_coef( 1, 1);
64  // compute S square root of h (using sqrtmod)
65  polyn_gf2m S(t - 1, g.get_sp_field());
66 
67  for(uint32_t i=0;i<t;i++)
68  {
69  a = sp_field->gf_sqrt(h.get_coef(i));
70 
71  if(i & 1)
72  {
73  for(uint32_t j=0;j<t;j++)
74  {
75  S.add_to_coef( j, sp_field->gf_mul(a, sqrtmod[i/2].get_coef(j)));
76  }
77  }
78  else
79  {
80  S.add_to_coef( i/2, a);
81  }
82  } /* end for loop (i) */
83 
84 
85  S.get_degree();
86 
87  std::pair<polyn_gf2m, polyn_gf2m> v_u = polyn_gf2m::eea_with_coefficients(S, g, t/2+1);
88  polyn_gf2m & u = v_u.second;
89  polyn_gf2m & v = v_u.first;
90 
91  // sigma = u^2+z*v^2
92  polyn_gf2m sigma ( t , g.get_sp_field());
93 
94  const int u_deg = u.get_degree();
95  BOTAN_ASSERT(u_deg >= 0, "Valid degree");
96  for(int i = 0; i <= u_deg; ++i)
97  {
98  sigma.set_coef(2*i, sp_field->gf_square(u.get_coef(i)));
99  }
100 
101  const int v_deg = v.get_degree();
102  BOTAN_ASSERT(v_deg >= 0, "Valid degree");
103  for(int i = 0; i <= v_deg; ++i)
104  {
105  sigma.set_coef(2*i+1, sp_field->gf_square(v.get_coef(i)));
106  }
107 
108  secure_vector<gf2m> res = find_roots_gf2m_decomp(sigma, code_length);
109  size_t d = res.size();
110 
111  secure_vector<gf2m> result(d);
112  for(uint32_t i = 0; i < d; ++i)
113  {
114  gf2m current = res[i];
115 
116  gf2m tmp;
117  tmp = gray_to_lex(current);
118  /// XXX double assignment, possible bug?
119  if(tmp >= code_length) /* invalid root */
120  {
121  result[i] = static_cast<gf2m>(i);
122  }
123  result[i] = Linv[tmp];
124  }
125 
126  return result;
127  }
128 }
129 
131  secure_vector<uint8_t>& error_mask_out,
132  const secure_vector<uint8_t>& ciphertext,
133  const McEliece_PrivateKey& key)
134  {
135  mceliece_decrypt(plaintext_out, error_mask_out, ciphertext.data(), ciphertext.size(), key);
136  }
137 
139  secure_vector<uint8_t>& plaintext,
140  secure_vector<uint8_t> & error_mask,
141  const uint8_t ciphertext[],
142  size_t ciphertext_len,
143  const McEliece_PrivateKey & key)
144  {
145  secure_vector<gf2m> error_pos;
146  plaintext = mceliece_decrypt(error_pos, ciphertext, ciphertext_len, key);
147 
148  const size_t code_length = key.get_code_length();
149  secure_vector<uint8_t> result((code_length+7)/8);
150  for(auto&& pos : error_pos)
151  {
152  if(pos > code_length)
153  {
154  throw Invalid_Argument("error position larger than code size");
155  }
156  result[pos / 8] |= (1 << (pos % 8));
157  }
158 
159  error_mask = result;
160  }
161 
162 /**
163 * @p p_err_pos_len must point to the available length of @p error_pos on input, the
164 * function will set it to the actual number of errors returned in the @p error_pos
165 * array */
167  secure_vector<gf2m> & error_pos,
168  const uint8_t *ciphertext, size_t ciphertext_len,
169  const McEliece_PrivateKey & key)
170  {
171 
172  const size_t dimension = key.get_dimension();
173  const size_t codimension = key.get_codimension();
174  const uint32_t t = key.get_goppa_polyn().get_degree();
175  polyn_gf2m syndrome_polyn(key.get_goppa_polyn().get_sp_field()); // init as zero polyn
176  const unsigned unused_pt_bits = dimension % 8;
177  const uint8_t unused_pt_bits_mask = (1 << unused_pt_bits) - 1;
178 
179  if(ciphertext_len != (key.get_code_length()+7)/8)
180  {
181  throw Invalid_Argument("wrong size of McEliece ciphertext");
182  }
183  const size_t cleartext_len = (key.get_message_word_bit_length()+7)/8;
184 
185  if(cleartext_len != bit_size_to_byte_size(dimension))
186  {
187  throw Invalid_Argument("mce-decryption: wrong length of cleartext buffer");
188  }
189 
190  secure_vector<uint32_t> syndrome_vec(bit_size_to_32bit_size(codimension));
191  matrix_arr_mul(key.get_H_coeffs(),
192  key.get_code_length(),
193  bit_size_to_32bit_size(codimension),
194  ciphertext,
195  syndrome_vec.data(), syndrome_vec.size());
196 
197  secure_vector<uint8_t> syndrome_byte_vec(bit_size_to_byte_size(codimension));
198  const size_t syndrome_byte_vec_size = syndrome_byte_vec.size();
199  for(size_t i = 0; i < syndrome_byte_vec_size; i++)
200  {
201  syndrome_byte_vec[i] = static_cast<uint8_t>(syndrome_vec[i/4] >> (8 * (i % 4)));
202  }
203 
204  syndrome_polyn = polyn_gf2m(t-1, syndrome_byte_vec.data(), bit_size_to_byte_size(codimension), key.get_goppa_polyn().get_sp_field());
205 
206  syndrome_polyn.get_degree();
207  error_pos = goppa_decode(syndrome_polyn, key.get_goppa_polyn(), key.get_sqrtmod(), key.get_Linv());
208 
209  const size_t nb_err = error_pos.size();
210 
211  secure_vector<uint8_t> cleartext(cleartext_len);
212  copy_mem(cleartext.data(), ciphertext, cleartext_len);
213 
214  for(size_t i = 0; i < nb_err; i++)
215  {
216  gf2m current = error_pos[i];
217 
218  if(current >= cleartext_len * 8)
219  {
220  // an invalid position, this shouldn't happen
221  continue;
222  }
223  cleartext[current / 8] ^= (1 << (current % 8));
224  }
225 
226  if(unused_pt_bits)
227  {
228  cleartext[cleartext_len - 1] &= unused_pt_bits_mask;
229  }
230 
231  return cleartext;
232  }
233 
234 }
std::vector< polyn_gf2m > const & get_sqrtmod() const
Definition: mceliece.h:102
size_t get_dimension() const
Definition: mceliece.h:104
void mceliece_decrypt(secure_vector< uint8_t > &plaintext_out, secure_vector< uint8_t > &error_mask_out, const secure_vector< uint8_t > &ciphertext, const McEliece_PrivateKey &key)
Definition: goppa_code.cpp:130
int get_degree() const
Definition: polyn_gf2m.cpp:228
polyn_gf2m const & get_goppa_polyn() const
Definition: mceliece.h:99
size_t get_message_word_bit_length() const
size_t get_code_length() const
Definition: mceliece.h:50
size_t bit_size_to_32bit_size(size_t bit_size)
std::vector< uint32_t > const & get_H_coeffs() const
Definition: mceliece.h:100
#define BOTAN_ASSERT(expr, assertion_made)
Definition: assert.h:55
gf2m gray_to_lex(gf2m gray)
std::vector< gf2m > const & get_Linv() const
Definition: mceliece.h:101
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
static std::pair< polyn_gf2m, polyn_gf2m > eea_with_coefficients(const polyn_gf2m &p, const polyn_gf2m &g, int break_deg)
Definition: polyn_gf2m.cpp:448
size_t get_codimension() const
Definition: mceliece.h:106
std::vector< T, secure_allocator< T > > secure_vector
Definition: secmem.h:65
std::shared_ptr< GF2m_Field > get_sp_field() const
Definition: polyn_gf2m.h:82
secure_vector< gf2m > find_roots_gf2m_decomp(const polyn_gf2m &polyn, size_t code_length)