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alternant decoder

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This commit is contained in:
Mirek Kratochvil 2012-11-05 21:30:08 +01:00
parent 5b6f4b61cb
commit 6d5b4c1feb
7 changed files with 86 additions and 14 deletions
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5
include/codecrypt.h
View file

@ -215,6 +215,10 @@ public:
void shift (uint);
uint eval (uint, gf2m&) const;
uint head() {
if ( (t = degree() ) >= 0) return item (t);
else return 0;
}
void add (const polynomial&, gf2m&);
void mult (const polynomial&, gf2m&);
void add_mult (const polynomial&, uint mult, gf2m&);
@ -228,6 +232,7 @@ public:
void sqrt (vector<polynomial>&, gf2m&);
polynomial gcd (polynomial, gf2m&);
void mod_to_fracton (polynomial&, polynomial&, polynomial&, gf2m&);
void ext_euclid (polynomial&, polynomial&, polynomial&, gf2m&, int);
bool is_irreducible (gf2m&) const;
void generate_random_irreducible (uint s, gf2m&, prng&);

30
lib/decoding.cpp
View file

@ -1,8 +1,10 @@
#include "decoding.h"
void compute_error_locator (polynomial&syndrome, gf2m&fld, polynomial& goppa,
std::vector<polynomial>& sqInv, polynomial&out)
void compute_goppa_error_locator (polynomial&syndrome, gf2m&fld,
polynomial& goppa,
std::vector<polynomial>& sqInv,
polynomial&out)
{
if (syndrome.zero() ) {
//ensure no roots
@ -30,6 +32,30 @@ void compute_error_locator (polynomial&syndrome, gf2m&fld, polynomial& goppa,
out = a;
}
void compute_alternant_error_locator (polynomial&syndrome, gf2m&fld,
uint t, polynomial&out)
{
if (syndrome.zero() ) {
//ensure no roots
out.resize (1);
out[0] = 1;
return;
}
polynomial a, b;
polynomial x2t; //should be x^2t
x2t.clear();
x2t.resize (1, 1);
x2t.shift (2 * t);
syndrome.ext_euclid (a, b, x2t, fld, t - 1);
uint b0inv = fld.inv (b[0]);
for (uint i = 0; i < b.size(); ++i) b[i] = fld.mult (b[i], b0inv);
out = b;
//we don't care about error evaluator
}
bool evaluate_error_locator_dumb (polynomial&a, bvector&ev, gf2m&fld)
{
ev.clear();

7
lib/decoding.h
View file

@ -6,12 +6,17 @@
using namespace ccr;
void compute_error_locator (polynomial&syndrome,
void compute_goppa_error_locator (polynomial&syndrome,
gf2m&fld,
polynomial&goppa,
std::vector<polynomial>& sqInv,
polynomial&loc);
void compute_alternant_error_locator (polynomial&syndrome,
gf2m&fld,
uint tt,
polynomial&loc);
bool evaluate_error_locator_dumb (polynomial&el, bvector&ev, gf2m&fld);
bool evaluate_error_locator_trace (polynomial&el, bvector&ev, gf2m&fld);

4
lib/mce.cpp
View file

@ -80,7 +80,7 @@ int privkey::decrypt (const bvector&in, bvector&out)
//decode
polynomial synd, loc;
syndrome.to_poly (synd, fld);
compute_error_locator (synd, fld, g, sqInv, loc);
compute_goppa_error_locator (synd, fld, g, sqInv, loc);
bvector ev;
if (!evaluate_error_locator_trace (loc, ev, fld) )
@ -144,7 +144,7 @@ int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prn
}
synd.to_poly (Synd, fld);
compute_error_locator (Synd, fld, g, sqInv, loc);
compute_goppa_error_locator (Synd, fld, g, sqInv, loc);
if (evaluate_error_locator_trace (loc, e2, fld) ) {

2
lib/mce_oc.cpp
View file

@ -124,7 +124,7 @@ int privkey::sign (const bvector&in, bvector&out,
}
synd.to_poly (Synd, fld);
compute_error_locator (Synd, fld,
compute_goppa_error_locator (Synd, fld,
codes[ci].g,
codes[ci].sqInv, loc);

4
lib/nd.cpp
View file

@ -59,7 +59,7 @@ int privkey::decrypt (const bvector&in, bvector&out)
polynomial loc, synd;
unsc.to_poly (synd, fld);
compute_error_locator (synd, fld, g, sqInv, loc);
compute_goppa_error_locator (synd, fld, g, sqInv, loc);
bvector ev;
if (!evaluate_error_locator_trace (loc, ev, fld) )
@ -93,7 +93,7 @@ int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prn
Sinv.mult_vec_right (synd, synd_unsc);
synd_unsc.to_poly (Synd, fld);
compute_error_locator (Synd, fld, g, sqInv, loc);
compute_goppa_error_locator (Synd, fld, g, sqInv, loc);
if (evaluate_error_locator_trace (loc, e, fld) ) {

36
lib/polynomial.cpp
View file

@ -339,9 +339,45 @@ void polynomial::inv (polynomial&m, gf2m&fld)
div (a, m, fld);
}
void polynomial::ext_euclid (polynomial&a_out, polynomial&b_out,
polynomial&m, gf2m&fld, int deg)
{
//TODO: speed this up (spare degree calculations)
polynomial A, B, a, b, tmp;
int j;
uint h;
A = *this;
a = m;
B.clear();
B.resize (1, 1);
b.clear();
while (a.degree() > deg) {
if (A.degree() < 0)
break;
A.swap (a);
B.swap (b);
while ( (j = A.degree() - a.degree() ) >= 0) {
h = fld.mult (A.head(), fld.inv (a.head() ) );
tmp = a;
tmp.shift (j);
A.add_mult (tmp, h, fld);
tmp = b;
tmp.shift (j);
B.add_mult (tmp, h, fld);
}
}
a.swap (a_out);
b.swap (b_out);
}
void polynomial::mod_to_fracton (polynomial&a, polynomial&b,
polynomial&m, gf2m&fld)
{
//TODO: replace with ext_euclid
int deg = m.degree() / 2;
polynomial a0, a1, b0, b1, q, r;
a0 = m;