3 files changed, 27 insertions, 20 deletions
diff --git a/src/lib/pubkey/mce/code_based_key_gen.cpp b/src/lib/pubkey/mce/code_based_key_gen.cpp
index f83e23b05..8fb290386 100644
--- a/src/lib/pubkey/mce/code_based_key_gen.cpp
+++ b/src/lib/pubkey/mce/code_based_key_gen.cpp
@@ -4,6 +4,7 @@
  *
  * (C) 2014 cryptosource GmbH
  * (C) 2014 Falko Strenzke [email protected]
+ * (C) 2015 Jack Lloyd
  *
  * Botan is released under the Simplified BSD License (see license.txt)
  *
@@ -134,21 +135,14 @@ secure_vector<int> binary_matrix::row_reduced_echelon_form()
    return perm;
    }
 
-void randomize_support(u32bit n, std::vector<gf2m> & L, RandomNumberGenerator & rng)
+void randomize_support(std::vector<gf2m>& L, RandomNumberGenerator& rng)
    {
-   unsigned int i, j;
-   gf2m tmp;
-
-   for (i = 0; i < n; ++i)
+   for(u32bit i = 0; i != L.size(); ++i)
       {
+      gf2m rnd = random_gf2m(rng);
 
-      gf2m rnd;
-      rng.randomize(reinterpret_cast<byte*>(&rnd), sizeof(rnd));
-      j = rnd % n; // no rejection sampling, but for useful code-based parameters with n <= 13 this seem tolerable
-
-      tmp = L[j];
-      L[j] = L[i];
-      L[i] = tmp;
+       // no rejection sampling, but for useful code-based parameters with n <= 13 this seem tolerable
+      std::swap(L[i], L[rnd % L.size()]);
       }
    }
 
@@ -235,7 +229,7 @@ McEliece_PrivateKey generate_mceliece_key( RandomNumberGenerator & rng, u32bit e
       {
       L[i]=i;
       }
-   randomize_support(code_length,L,rng);
+   randomize_support(L, rng);
    polyn_gf2m g(sp_field); // create as zero
    bool success = false;
    do
diff --git a/src/lib/pubkey/mce/polyn_gf2m.cpp b/src/lib/pubkey/mce/polyn_gf2m.cpp
index 4d9bcf2e8..ec60213db 100644
--- a/src/lib/pubkey/mce/polyn_gf2m.cpp
+++ b/src/lib/pubkey/mce/polyn_gf2m.cpp
@@ -4,6 +4,7 @@
  *
  * (C) 2014 cryptosource GmbH
  * (C) 2014 Falko Strenzke [email protected]
+ * (C) 2015 Jack Lloyd
  *
  * Botan is released under the Simplified BSD License (see license.txt)
  *
@@ -14,6 +15,7 @@
 #include <botan/internal/bit_ops.h>
 #include <botan/rng.h>
 #include <botan/exceptn.h>
+#include <botan/loadstor.h>
 
 namespace Botan {
 
@@ -25,6 +27,9 @@ gf2m generate_gf2m_mask(gf2m a)
    return ~(result - 1);
    }
 
+/**
+* number of leading zeros
+*/
 unsigned nlz_16bit(u16bit x)
    {
    unsigned n;
@@ -55,24 +60,31 @@ int polyn_gf2m::calc_degree_secure() const
    const_cast<polyn_gf2m*>(this)->m_deg = result;
    return result;
    }
-/**
-* number of leading zeros
-*/
 
-gf2m random_code_element(unsigned code_length, Botan::RandomNumberGenerator& rng)
+gf2m random_gf2m(RandomNumberGenerator& rng)
+   {
+   byte b[2];
+   rng.randomize(b, sizeof(b));
+   return make_u16bit(b[1], b[0]);
+   }
+
+gf2m random_code_element(unsigned code_length, RandomNumberGenerator& rng)
    {
    if(code_length == 0)
       {
       throw Invalid_Argument("random_code_element() was supplied a code length of zero");
       }
-   unsigned nlz = nlz_16bit(code_length-1);
-   gf2m mask = (1 << (16-nlz)) -1;
+   const unsigned nlz = nlz_16bit(code_length-1);
+   const gf2m mask = (1 << (16-nlz)) -1;
+
    gf2m result;
+
    do
       {
-      rng.randomize(reinterpret_cast<byte*>(&result), sizeof(result));
+      result = random_gf2m(rng);
       result &= mask;
       } while(result >= code_length); // rejection sampling
+
    return result;
    }
 
diff --git a/src/lib/pubkey/mce/polyn_gf2m.h b/src/lib/pubkey/mce/polyn_gf2m.h
index 1c8cc5211..5d012f27b 100644
--- a/src/lib/pubkey/mce/polyn_gf2m.h
+++ b/src/lib/pubkey/mce/polyn_gf2m.h
@@ -152,6 +152,7 @@ struct polyn_gf2m
       std::shared_ptr<GF2m_Field> msp_field;
    };
 
+gf2m random_gf2m(RandomNumberGenerator& rng);
 gf2m random_code_element(unsigned code_length, RandomNumberGenerator& rng);
 
 std::vector<polyn_gf2m> syndrome_init(polyn_gf2m const& generator, std::vector<gf2m> const& support, int n);