niederreiter + various related fixes

include/codecrypt.h

@@ -4,7 +4,7 @@
 
 #include <vector>
 
-//STL wraparound, because writing (*this)[i] everywhere is clumsy
+//little STL helper, because writing (*this)[i] everywhere is clumsy
 #define _ccr_declare_vector_item \
 	inline reference item(size_type n) \
 		{ return (*this)[n]; }; \
@@ -233,10 +233,33 @@ namespace nd
 class privkey
 {
 public:
-	// TODO
+	matrix Sinv;
+	permutation Pinv;
+	polynomial g;
+	gf2m fld;
+
+	//derivable.
+	std::vector<polynomial> sqInv;
 
 	int decrypt (const bvector&, bvector&);
 	int sign (const bvector&, bvector&, uint, uint, prng&);
+	int prepare();
+
+	uint cipher_size() {
+		return Pinv.size();
+	}
+	uint plain_size() {
+		return Sinv.width();
+	}
+	uint plain_weight() {
+		return g.degree();
+	}
+	uint hash_size() {
+		return cipher_size();
+	}
+	uint signature_size() {
+		return plain_size();
+	}
 };
 
 class pubkey
@@ -245,11 +268,27 @@ public:
 	matrix H;
 	uint t;
 
-	int encrypt (const bvector&, bvector&, prng&);
+	int encrypt (const bvector&, bvector&);
 	int verify (const bvector&, const bvector&, uint);
+
+	uint cipher_size() {
+		return H.height();
+	}
+	uint plain_size() {
+		return H.width();
+	}
+	uint plain_weight() {
+		return t;
+	}
+	uint hash_size() {
+		return cipher_size();
+	}
+	uint signature_size() {
+		return plain_size();
+	}
 };
 
-int generate (pubkey&, privkey&, prng&);
+int generate (pubkey&, privkey&, prng&, uint m, uint t);
 }
 
 } //namespace ccr

lib/decoding.cpp

@@ -50,5 +50,10 @@ bool syndrome_decode (bvector&syndrome, gf2m&fld, polynomial& goppa,
 		}
 	}
 
+	if (check_failure && a.degree() > 0) {
+		ev.clear();
+		return false;
+	}
+
 	return true;
 }

lib/mce.cpp

@@ -6,7 +6,7 @@ using namespace ccr::mce;
 
 #include "decoding.h"
 
-int ccr::mce::generate (pubkey&pub, privkey&priv, prng&rng, uint m, uint t)
+int mce::generate (pubkey&pub, privkey&priv, prng&rng, uint m, uint t)
 {
 	//finite field
 	priv.fld.create (m);
@@ -80,9 +80,8 @@ int privkey::decrypt (const bvector&in, bvector&out)
 
 	//decode
 	bvector ev;
-	if (!syndrome_decode (syndrome, fld, g, sqInv, ev) ) {
+	if (!syndrome_decode (syndrome, fld, g, sqInv, ev) )
 		return 1; //if decoding somehow failed, fail as well.
-	}
 
 	// check the error vector, it should have exactly t == deg (g) errors
 	if ( (int) ev.hamming_weight() != g.degree() )
@@ -112,8 +111,8 @@ int privkey::prepare ()
 
 int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prng&rng)
 {
-	uint i, t, s;
-	bvector p, e, synd, synd2, e2;
+	uint i, s, t;
+	bvector p, e, synd, synd_orig, e2;
 	std::vector<uint> epos;
 	permutation hpermInv;
 
@@ -130,34 +129,39 @@ int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prn
 	e.resize (s, 0);
 	epos.resize (delta, 0);
 
-	h.mult_vec_right (p, synd);
+	h.mult_vec_right (p, synd_orig);
 
 	for (t = 0; t < attempts; ++t) {
+
+		synd = synd_orig;
+
 		for (i = 0; i < delta; ++i) {
 			epos[i] = rng.random (s);
 			/* we don't care about (unlikely) error bit collisions
 			   (they actually don't harm anything) */
 			e[epos[i]] = 1;
+			synd.add (h[epos[i]]);
 		}
 
-		//abuse linearity of p+e; it is usually faster.
-		h.mult_vec_right (e, synd2);
-		synd2.add (synd);
+		if (syndrome_decode (synd, fld, g, sqInv, e2, true) ) {
 
-		if (syndrome_decode (synd2, fld, g, sqInv, e2) ) {
-			//decoding success!
-			p.add (e); //add original errors
-			hperm.permute (p, e2); //back to systematic (e2 is tmp)
-			e2.resize (signature_size() ); //strip redundancy
-			Sinv.mult_vecT_left (e2, out); //get a signature
-			return 0; //OK lol
+			//create the decodable message
+			p.add(e);
+			p.add(e2);
+
+			hperm.permute (p, e2); //back to systematic
+			e2.resize (signature_size() ); //strip checks
+			Sinv.mult_vecT_left (e2, out); //signature
+			return 0;
 		}
 
 		//if this round failed, we try a new error pattern.
 
-		for (i = 0; i < delta; ++i) //clear the errors for the next cycle
+		for (i = 0; i < delta; ++i) {
+			//clear the errors for next cycle
 			e[epos[i]] = 0;
 		}
+	}
 	return 1; //couldn't decode
 }
 

lib/nd.cpp

@@ -1,35 +1,100 @@
 
 #include "codecrypt.h"
 
+#include "decoding.h"
+
 using namespace ccr;
 using namespace ccr::nd;
 
-int nd::generate (pubkey&pub, privkey&priv, prng&rng)
+int nd::generate (pubkey&pub, privkey&priv, prng&rng, uint m, uint t)
 {
+	//galois field
+	priv.fld.create (m);
 
-	return -1; //TODO
+	//goppa polynomial
+	priv.g.generate_random_irreducible (t, priv.fld, rng);
+
+	matrix h;
+	priv.g.compute_goppa_check_matrix (h, priv.fld);
+
+	//scrambler
+	matrix S;
+	S.generate_random_invertible (h.height(), rng);
+	S.compute_inversion (priv.Sinv);
+
+	//permutation
+	permutation P;
+	P.generate_random (h.width(), rng);
+	P.compute_inversion (priv.Pinv);
+
+	//pubkey
+	pub.t = t;
+	S.mult (h);
+	P.permute (S, pub.H);
+
+	return 0;
 }
 
-int pubkey::encrypt (const bvector& in, bvector&out, prng&rng)
+int pubkey::encrypt (const bvector& in, bvector&out)
 {
-
-	return -1; //TODO
+	if (in.size() != plain_size() ) return 1;
+	H.mult_vec_right (in, out);
+	return 0;
 }
 
 int privkey::decrypt (const bvector&in, bvector&out)
 {
+	if (in.size() != cipher_size() ) return 2;
 
-	return -1; //TODO
+	bvector unsc; //unscrambled
+	Sinv.mult_vec_right (in, unsc);
+
+	bvector ev;
+	if (!syndrome_decode (unsc, fld, g, sqInv, ev) )
+		return 1;
+
+	if ( (int) ev.hamming_weight() != g.degree() )
+		return 1;
+
+	Pinv.permute (ev, out);
+	return 0;
 }
 
-int privkey::sign (const bvector&in, bvector&out, uint delta, uint h, prng&rng)
+int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prng&rng)
 {
+	uint i, s, t;
 
-	return -1; //TODO
+	bvector synd_orig, synd, e;
+
+	s = hash_size();
+	if (in.size() != s) return 2;
+
+	Sinv.mult_vec_right (in, synd_orig);
+
+	for (t = 0; t < attempts; ++t) {
+
+		synd = synd_orig;
+		for (i = 0; i < delta; ++i) {
+			uint pos = rng.random (s);
+			synd[pos] = !synd[pos]; //flip a bit
+		}
+
+		if (syndrome_decode (synd, fld, g, sqInv, e, true) ) {
+
+			Pinv.permute (e, out);
+			return 0;
+		}
+	}
+
+	return 1;
 }
 
 int pubkey::verify (const bvector&in, const bvector&hash, uint delta)
 {
-
-	return -1; //TODO
+	bvector tmp;
+	if (!H.mult_vec_right (in, tmp) ) return 2;
+	if (hash.size() != tmp.size() ) return 1;
+	tmp.add (hash);
+	if (tmp.hamming_weight() > delta) return 1;
+	return 0;
 }

src/main.cpp

@@ -26,7 +26,7 @@ int main()
 
 	ccr::mce::privkey priv;
 	ccr::mce::pubkey pub;
-	ccr::mce::generate (pub, priv, r, 7, 4);
+	ccr::mce::generate (pub, priv, r, 7, 2);
 
 	cout << "PRIVATE KEY" << endl;
 	cout << priv.fld;
@@ -38,6 +38,8 @@ int main()
 	cout << pub.t << endl;
 	cout << pub.G;
 
+	/* mce encryption test */
+
 	ccr::bvector plain;
 	plain.resize (pub.plain_size(), 0);
 	plain[0] = 1;
@@ -71,9 +73,9 @@ int main()
 	hash[2] = 1;
 
 	cout << "SIGNING" << endl << hash;
-	priv.sign (hash, signature, 2, priv.hash_size() *priv.hash_size(), r);
+	priv.sign (hash, signature, 3, priv.hash_size() *priv.hash_size(), r);
 	cout << "SIGNATURE" << endl << signature;
-	if (pub.verify (signature, hash, 2) )
+	if (pub.verify (signature, hash, 3) )
 		cout << "VERIFY FAIL" << endl;
 	else	cout << "VERIFY OK" << endl;
 	return 0;