diff options
Diffstat (limited to 'src/lib/pubkey/mce/polyn_gf2m.cpp')
| -rw-r--r-- | src/lib/pubkey/mce/polyn_gf2m.cpp | 26 |
1 files changed, 19 insertions, 7 deletions
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; } |