From 8bba17f75486d40c6aedd796714de1cee1420830 Mon Sep 17 00:00:00 2001
From: Mirek Kratochvil <exa.exa@gmail.com>
Date: Sat, 2 Jun 2012 11:55:58 +0200
Subject: [PATCH] nd: fixes

---
 include/codecrypt.h |  6 +++---
 lib/mce.cpp         |  4 ++--
 lib/nd.cpp          | 27 ++++++++++++++++++---------
 3 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/include/codecrypt.h b/include/codecrypt.h
index 3990c39..2bccedd 100644
--- a/include/codecrypt.h
+++ b/include/codecrypt.h
@@ -70,7 +70,7 @@ public:
 	}
 
 	matrix operator* (const matrix&);
-	void mult (const matrix&);
+	void mult (const matrix&); //right multiply - this*param
 
 	void compute_transpose (matrix&);
 	bool compute_inversion (matrix&);
@@ -246,10 +246,10 @@ public:
 	int prepare();
 
 	uint cipher_size() {
-		return Pinv.size();
+		return Sinv.size();
 	}
 	uint plain_size() {
-		return Sinv.width();
+		return Pinv.size();
 	}
 	uint plain_weight() {
 		return g.degree();
diff --git a/lib/mce.cpp b/lib/mce.cpp
index f239e49..5bdf726 100644
--- a/lib/mce.cpp
+++ b/lib/mce.cpp
@@ -146,8 +146,8 @@ int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prn
 		if (syndrome_decode (synd, fld, g, sqInv, e2, true) ) {
 
 			//create the decodable message
-			p.add(e);
-			p.add(e2);
+			p.add (e);
+			p.add (e2);
 
 			hperm.permute (p, e2); //back to systematic
 			e2.resize (signature_size() ); //strip checks
diff --git a/lib/nd.cpp b/lib/nd.cpp
index a552d54..78b746b 100644
--- a/lib/nd.cpp
+++ b/lib/nd.cpp
@@ -23,18 +23,27 @@ int nd::generate (pubkey&pub, privkey&priv, prng&rng, uint m, uint t)
 	S.compute_inversion (priv.Sinv);
 
 	//permutation
-	permutation P;
-	P.generate_random (h.width(), rng);
-	P.compute_inversion (priv.Pinv);
+	priv.Pinv.generate_random (h.width(), rng);
+
+	/*
+	 * note: we actually don't need the inversion, as it inverts itself
+	 * when permuting SH to pubkey.
+	 */
 
 	//pubkey
 	pub.t = t;
 	S.mult (h);
-	P.permute (S, pub.H);
+	priv.Pinv.permute (S, pub.H);
 
 	return 0;
 }
 
+int privkey::prepare ()
+{
+	g.compute_square_root_matrix (sqInv, fld);
+	return 0;
+}
+
 int pubkey::encrypt (const bvector& in, bvector&out)
 {
 	if (in.size() != plain_size() ) return 1;
@@ -64,22 +73,22 @@ int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prn
 {
 	uint i, s, t;
 
-	bvector synd_orig, synd, e;
+	bvector synd_unsc, 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;
+		synd = in;
 		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) ) {
+		Sinv.mult_vec_right (synd, synd_unsc);
+
+		if (syndrome_decode (synd_unsc, fld, g, sqInv, e, true) ) {
 
 			Pinv.permute (e, out);
 			return 0;