Botan  2.6.0
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  uint32_t numo_rows,
21  uint32_t words_per_row,
22  const uint8_t* input_vec,
23  uint32_t* output_vec, uint32_t output_vec_len)
24  {
25  for(size_t j = 0; j < numo_rows; j++)
26  {
27  if((input_vec[j / 8] >> (j % 8)) & 1)
28  {
29  for(size_t i = 0; i < output_vec_len; i ++)
30  {
31  output_vec[i] ^= matrix[ j * (words_per_row) + i];
32  }
33  }
34  }
35  }
36 
37 /**
38 * returns the error vector to the syndrome
39 */
40 secure_vector<gf2m> goppa_decode(const polyn_gf2m & syndrom_polyn,
41  const polyn_gf2m & g,
42  const std::vector<polyn_gf2m> & sqrtmod,
43  const std::vector<gf2m> & Linv)
44  {
45  gf2m a;
46  uint32_t code_length = Linv.size();
47  uint32_t t = g.get_degree();
48 
49  std::shared_ptr<GF2m_Field> sp_field = g.get_sp_field();
50 
51  std::pair<polyn_gf2m, polyn_gf2m> h_aux = polyn_gf2m::eea_with_coefficients( syndrom_polyn, g, 1);
52  polyn_gf2m & h = h_aux.first;
53  polyn_gf2m & aux = h_aux.second;
54  a = sp_field->gf_inv(aux.get_coef(0));
55  gf2m log_a = sp_field->gf_log(a);
56  for(int i = 0; i <= h.get_degree(); ++i)
57  {
58  h.set_coef(i,sp_field->gf_mul_zrz(log_a,h.get_coef(i)));
59  }
60 
61  // compute h(z) += z
62  h.add_to_coef( 1, 1);
63  // compute S square root of h (using sqrtmod)
64  polyn_gf2m S(t - 1, g.get_sp_field());
65 
66  for(uint32_t i=0;i<t;i++)
67  {
68  a = sp_field->gf_sqrt(h.get_coef(i));
69 
70  if(i & 1)
71  {
72  for(uint32_t j=0;j<t;j++)
73  {
74  S.add_to_coef( j, sp_field->gf_mul(a, sqrtmod[i/2].get_coef(j)));
75  }
76  }
77  else
78  {
79  S.add_to_coef( i/2, a);
80  }
81  } /* end for loop (i) */
82 
83 
84  S.get_degree();
85 
86  std::pair<polyn_gf2m, polyn_gf2m> v_u = polyn_gf2m::eea_with_coefficients(S, g, t/2+1);
87  polyn_gf2m & u = v_u.second;
88  polyn_gf2m & v = v_u.first;
89 
90  // sigma = u^2+z*v^2
91  polyn_gf2m sigma ( t , g.get_sp_field());
92 
93  const size_t u_deg = u.get_degree();
94  for(size_t i = 0; i <= u_deg; ++i)
95  {
96  sigma.set_coef(2*i, sp_field->gf_square(u.get_coef(i)));
97  }
98 
99  const int v_deg = v.get_degree();
100  BOTAN_ASSERT(v_deg > 0, "Valid degree");
101  for(int i = 0; i <= v_deg; ++i)
102  {
103  sigma.set_coef(2*i+1, sp_field->gf_square(v.get_coef(i)));
104  }
105 
106  secure_vector<gf2m> res = find_roots_gf2m_decomp(sigma, code_length);
107  size_t d = res.size();
108 
109  secure_vector<gf2m> result(d);
110  for(uint32_t i = 0; i < d; ++i)
111  {
112  gf2m current = res[i];
113 
114  gf2m tmp;
115  tmp = gray_to_lex(current);
116  if(tmp >= code_length) /* invalid root */
117  {
118  result[i] = i;
119  }
120  result[i] = Linv[tmp];
121  }
122 
123  return result;
124  }
125 }
126 
128  secure_vector<uint8_t>& error_mask_out,
129  const secure_vector<uint8_t>& ciphertext,
130  const McEliece_PrivateKey& key)
131  {
132  mceliece_decrypt(plaintext_out, error_mask_out, ciphertext.data(), ciphertext.size(), key);
133  }
134 
136  secure_vector<uint8_t>& plaintext,
137  secure_vector<uint8_t> & error_mask,
138  const uint8_t ciphertext[],
139  size_t ciphertext_len,
140  const McEliece_PrivateKey & key)
141  {
142  secure_vector<gf2m> error_pos;
143  plaintext = mceliece_decrypt(error_pos, ciphertext, ciphertext_len, key);
144 
145  const size_t code_length = key.get_code_length();
146  secure_vector<uint8_t> result((code_length+7)/8);
147  for(auto&& pos : error_pos)
148  {
149  if(pos > code_length)
150  {
151  throw Invalid_Argument("error position larger than code size");
152  }
153  result[pos / 8] |= (1 << (pos % 8));
154  }
155 
156  error_mask = result;
157  }
158 
159 /**
160 * @p p_err_pos_len must point to the available length of @p error_pos on input, the
161 * function will set it to the actual number of errors returned in the @p error_pos
162 * array */
164  secure_vector<gf2m> & error_pos,
165  const uint8_t *ciphertext, uint32_t ciphertext_len,
166  const McEliece_PrivateKey & key)
167  {
168 
169  uint32_t dimension = key.get_dimension();
170  uint32_t codimension = key.get_codimension();
171  uint32_t t = key.get_goppa_polyn().get_degree();
172  polyn_gf2m syndrome_polyn(key.get_goppa_polyn().get_sp_field()); // init as zero polyn
173  const unsigned unused_pt_bits = dimension % 8;
174  const uint8_t unused_pt_bits_mask = (1 << unused_pt_bits) - 1;
175 
176  if(ciphertext_len != (key.get_code_length()+7)/8)
177  {
178  throw Invalid_Argument("wrong size of McEliece ciphertext");
179  }
180  uint32_t cleartext_len = (key.get_message_word_bit_length()+7)/8;
181 
182  if(cleartext_len != bit_size_to_byte_size(dimension))
183  {
184  throw Invalid_Argument("mce-decryption: wrong length of cleartext buffer");
185  }
186 
187  secure_vector<uint32_t> syndrome_vec(bit_size_to_32bit_size(codimension));
188  matrix_arr_mul(key.get_H_coeffs(),
189  key.get_code_length(),
190  bit_size_to_32bit_size(codimension),
191  ciphertext,
192  syndrome_vec.data(), syndrome_vec.size());
193 
194  secure_vector<uint8_t> syndrome_byte_vec(bit_size_to_byte_size(codimension));
195  uint32_t syndrome_byte_vec_size = syndrome_byte_vec.size();
196  for(uint32_t i = 0; i < syndrome_byte_vec_size; i++)
197  {
198  syndrome_byte_vec[i] = syndrome_vec[i/4] >> (8* (i % 4));
199  }
200 
201  syndrome_polyn = polyn_gf2m(t-1, syndrome_byte_vec.data(), bit_size_to_byte_size(codimension), key.get_goppa_polyn().get_sp_field());
202 
203  syndrome_polyn.get_degree();
204  error_pos = goppa_decode(syndrome_polyn, key.get_goppa_polyn(), key.get_sqrtmod(), key.get_Linv());
205 
206  uint32_t nb_err = error_pos.size();
207 
208  secure_vector<uint8_t> cleartext(cleartext_len);
209  copy_mem(cleartext.data(), ciphertext, cleartext_len);
210 
211  for(uint32_t i = 0; i < nb_err; i++)
212  {
213  gf2m current = error_pos[i];
214 
215  if(current >= cleartext_len * 8)
216  {
217  // an invalid position, this shouldn't happen
218  continue;
219  }
220  cleartext[current / 8] ^= (1 << (current % 8));
221  }
222 
223  if(unused_pt_bits)
224  {
225  cleartext[cleartext_len - 1] &= unused_pt_bits_mask;
226  }
227 
228  return cleartext;
229  }
230 
231 }
std::vector< polyn_gf2m > const & get_sqrtmod() const
Definition: mceliece.h:102
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:127
int get_degree() const
Definition: polyn_gf2m.cpp:230
uint32_t get_dimension() const
Definition: mceliece.h:104
polyn_gf2m const & get_goppa_polyn() const
Definition: mceliece.h:99
uint32_t bit_size_to_32bit_size(uint32_t bit_size)
uint32_t bit_size_to_byte_size(uint32_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:30
uint32_t get_codimension() const
Definition: mceliece.h:106
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:20
secure_vector< gf2m > find_roots_gf2m_decomp(const polyn_gf2m &polyn, uint32_t code_length)
void copy_mem(T *out, const T *in, size_t n)
Definition: mem_ops.h:108
Definition: alg_id.cpp:13
uint32_t get_code_length() const
Definition: mceliece.h:50
uint32_t code_length
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:450
uint32_t get_message_word_bit_length() const
std::vector< T, secure_allocator< T > > secure_vector
Definition: secmem.h:88
std::shared_ptr< GF2m_Field > get_sp_field() const
Definition: polyn_gf2m.h:74