1 files changed, 203 insertions, 0 deletions
diff --git a/src/lib/pubkey/mce/goppa_code.cpp b/src/lib/pubkey/mce/goppa_code.cpp
new file mode 100644
index 000000000..bc8fb7b32
--- /dev/null
+++ b/src/lib/pubkey/mce/goppa_code.cpp
@@ -0,0 +1,203 @@
+/**
+ * (C) Copyright Projet SECRET, INRIA, Rocquencourt
+ * (C) Bhaskar Biswas and  Nicolas Sendrier
+ *
+ * (C) 2014 cryptosource GmbH
+ * (C) 2014 Falko Strenzke [email protected]
+ *
+ * Distributed under the terms of the Botan license
+ *
+ */
+
+#include <botan/goppa_code.h>
+
+#include <botan/gf2m_rootfind_dcmp.h>
+#include <botan/code_based_util.h>
+
+namespace Botan {
+
+namespace {
+
+void matrix_arr_mul(std::vector<u32bit> matrix,
+                    u32bit numo_rows,
+                    u32bit words_per_row,
+                    const byte* input_vec,
+                    u32bit* output_vec, u32bit output_vec_len)
+   {
+   for(size_t j = 0; j < numo_rows; j++)
+      {
+      if((input_vec[j / 8] >> (j % 8)) & 1)
+         {
+         for(size_t i = 0; i < output_vec_len; i ++)
+            {
+            output_vec[i] ^= matrix[ j * (words_per_row) + i];
+            }
+         }
+      }
+   }
+
+/**
+* returns the error vector to the syndrome
+*/
+secure_vector<gf2m> goppa_decode(const polyn_gf2m & syndrom_polyn,
+                                 const polyn_gf2m & g,
+                                 const std::vector<polyn_gf2m> & sqrtmod,
+                                 const std::vector<gf2m> & Linv)
+   {
+   gf2m a;
+   u32bit code_length = Linv.size();
+   u32bit t = g.get_degree();
+
+   std::shared_ptr<gf2m_small_m::Gf2m_Field> sp_field = g.get_sp_field();
+
+   std::pair<polyn_gf2m, polyn_gf2m> h__aux = polyn_gf2m::eea_with_coefficients( syndrom_polyn, g, 1);
+   polyn_gf2m & h = h__aux.first;
+   polyn_gf2m & aux = h__aux.second;
+   a = sp_field->gf_inv(aux.get_coef(0));
+   gf2m log_a = sp_field->gf_log(a);
+   for(int i = 0; i <= h.get_degree(); ++i)
+      {
+      h.set_coef(i,sp_field->gf_mul_zrz(log_a,h.get_coef(i)));
+      }
+
+   //  compute h(z) += z
+   h.add_to_coef( 1, 1);
+   // compute S square root of h (using sqrtmod)
+   polyn_gf2m S(t - 1, g.get_sp_field());
+
+   for(u32bit i=0;i<t;i++)
+      {
+      a = sp_field->gf_sqrt(h.get_coef(i));
+
+      if(i & 1)
+         {
+         for(u32bit j=0;j<t;j++)
+            {
+            S.add_to_coef( j, sp_field->gf_mul(a, sqrtmod[i/2].get_coef(j)));
+            }
+         }
+      else
+         {
+         S.add_to_coef( i/2, a);
+         }
+      } /* end for loop (i) */
+
+
+   S.get_degree();
+
+   std::pair<polyn_gf2m, polyn_gf2m> v__u = polyn_gf2m::eea_with_coefficients(S, g, t/2+1);
+   polyn_gf2m & u = v__u.second;
+   polyn_gf2m & v = v__u.first;
+
+   // sigma = u^2+z*v^2
+   polyn_gf2m sigma ( t , g.get_sp_field());
+
+   const size_t u_deg = u.get_degree();
+   for(size_t i = 0; i <= u_deg; ++i)
+      {
+      sigma.set_coef(2*i, sp_field->gf_square(u.get_coef(i)));
+      }
+
+   const size_t v_deg = v.get_degree();
+   for(size_t i = 0; i <= v_deg; ++i)
+      {
+      sigma.set_coef(2*i+1, sp_field->gf_square(v.get_coef(i)));
+      }
+
+   secure_vector<gf2m> res = find_roots_gf2m_decomp(sigma, code_length);
+   size_t d = res.size();
+
+   secure_vector<gf2m> result(d);
+   for(u32bit i = 0; i < d; ++i)
+      {
+      gf2m current = res[i];
+
+      gf2m tmp;
+      tmp = gray_to_lex(current);
+      if(tmp >= code_length) /* invalid root */
+         {
+         result[i] = i;
+         }
+      result[i] = Linv[tmp];
+      }
+
+   return result;
+   }
+}
+
+
+/**
+* @param p_err_pos_len must point to the available length of err_pos on input, the
+* function will set it to the actual number of errors returned in the err_pos
+* array */
+secure_vector<byte> mceliece_decrypt(
+   secure_vector<gf2m> & error_pos,
+   const byte *ciphertext, u32bit ciphertext_len,
+   const McEliece_PrivateKey & key)
+   {
+
+   u32bit dimension = key.get_dimension();
+   u32bit codimension = key.get_codimension();
+   u32bit t = key.get_goppa_polyn().get_degree();
+   polyn_gf2m syndrome_polyn(key.get_goppa_polyn().get_sp_field()); // init as zero polyn
+   const unsigned unused_pt_bits = dimension % 8;
+   const unsigned char unused_pt_bits_mask = (1 << unused_pt_bits) - 1;
+
+   if(ciphertext_len != (key.get_code_length()+7)/8)
+      {
+      throw Invalid_Argument("wrong size of McEliece ciphertext");
+      }
+   u32bit cleartext_len = (key.get_message_word_bit_length()+7)/8;
+
+   if(cleartext_len != bit_size_to_byte_size(dimension))
+      {
+      throw Invalid_Argument("mce-decryption: wrong length of cleartext buffer");
+      }
+
+
+   secure_vector<u32bit> syndrome_vec(bit_size_to_32bit_size(codimension));
+   matrix_arr_mul(
+      key.get_H_coeffs(),
+      key.get_code_length(),
+      bit_size_to_32bit_size(codimension),
+      ciphertext,
+      &syndrome_vec[0], syndrome_vec.size() );
+   secure_vector<byte> syndrome_byte_vec(bit_size_to_byte_size(codimension));
+   u32bit syndrome_byte_vec_size = syndrome_byte_vec.size();
+   for(u32bit i = 0; i < syndrome_byte_vec_size; i++)
+      {
+      syndrome_byte_vec[i] = syndrome_vec[i/4] >> (8* (i % 4));
+      }
+   syndrome_polyn = polyn_gf2m( t-1, &syndrome_byte_vec[0],bit_size_to_byte_size(codimension), key.get_goppa_polyn().get_sp_field());
+
+
+
+   syndrome_polyn.get_degree();
+   error_pos = goppa_decode(syndrome_polyn, key.get_goppa_polyn(), key.get_sqrtmod(), key.get_Linv());
+
+   u32bit nb_err = error_pos.size();
+
+
+   secure_vector<byte> cleartext(cleartext_len);
+   std::memcpy(&cleartext[0], ciphertext, cleartext_len);
+
+   for(u32bit i = 0; i < nb_err; i++)
+      {
+      gf2m current = error_pos[i];
+
+      if(current >= cleartext_len * 8)
+         {
+         // an invalid position, this shouldn't happen
+         continue;
+         }
+      cleartext[current / 8] ^= (1 << (current % 8));
+      }
+   if(unused_pt_bits)
+      {
+      cleartext[cleartext_len - 1] &= unused_pt_bits_mask;
+      }
+
+   return cleartext;
+   }
+
+}