From: Andreas Steffen <andreas.steffen@strongswan.org>
Date: Thu, 3 Sep 2015 11:24:08 +0000 (+0200)
Subject: ntru: Define small modulus p = 3 for trits as a constant
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fheads%2Fntru-ng;p=thirdparty%2Fstrongswan.git

ntru: Define small modulus p = 3 for trits as a constant
---

diff --git a/src/libstrongswan/plugins/ntru/ntru_convert.c b/src/libstrongswan/plugins/ntru/ntru_convert.c
index 6330b2e39f..ffdd5c6d5c 100644
--- a/src/libstrongswan/plugins/ntru/ntru_convert.c
+++ b/src/libstrongswan/plugins/ntru/ntru_convert.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2014 Andreas Steffen
+ * Copyright (C) 2014-2015 Andreas Steffen
  * HSR Hochschule fuer Technik Rapperswil
  *
  * Copyright (C) 2009-2013  Security Innovation
@@ -269,8 +269,8 @@ void ntru_octet_2_trits(uint8_t octet, uint8_t *trits)
 
 	for (i = 0; i < 5; i++)
 	{
-		trits[i] = octet % 3;
-		octet = (octet - trits[i]) / 3;
+		trits[i] = octet % p;
+		octet = (octet - trits[i]) / p;
 	}
 }
 
diff --git a/src/libstrongswan/plugins/ntru/ntru_convert.h b/src/libstrongswan/plugins/ntru/ntru_convert.h
index 31594b1f6c..84139d92d4 100644
--- a/src/libstrongswan/plugins/ntru/ntru_convert.h
+++ b/src/libstrongswan/plugins/ntru/ntru_convert.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2014 Andreas Steffen
+ * Copyright (C) 2014-2015 Andreas Steffen
  * HSR Hochschule fuer Technik Rapperswil
  *
  * Copyright (C) 2009-2013  Security Innovation
@@ -25,6 +25,11 @@
 
 #include <library.h>
 
+/**
+ * Define small modulus p = 3 used for trits
+ */
+#define p   3
+
 /**
  * Each 3 bits in an array of octets is converted to 2 trits in an array
  * of trits.
diff --git a/src/libstrongswan/plugins/ntru/ntru_private_key.c b/src/libstrongswan/plugins/ntru/ntru_private_key.c
index fa87fe9c31..b0dab1146e 100644
--- a/src/libstrongswan/plugins/ntru/ntru_private_key.c
+++ b/src/libstrongswan/plugins/ntru/ntru_private_key.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2014 Andreas Steffen
+ * Copyright (C) 2014-2015 Andreas Steffen
  * HSR Hochschule fuer Technik Rapperswil
  *
  * Copyright (C) 2009-2013  Security Innovation
@@ -212,7 +212,7 @@ METHOD(ntru_private_key_t, decrypt, bool,
 
 	/* set constants */
 	mod_q_mask = this->params->q - 1;
-	q_mod_p = this->params->q % 3;
+	q_mod_p = this->params->q % p;
 
     /* unpack the ciphertext */
     ntru_octets_2_elements(ciphertext.len, ciphertext.ptr,
@@ -232,12 +232,12 @@ METHOD(ntru_private_key_t, decrypt, bool,
 		--cmprime_len;
 		for (i = 0; i < cmprime_len; i++)
 		{
-			t1[i] = (t2[i] + 3 * t1[i]) & mod_q_mask;
+			t1[i] = (t2[i] + p * t1[i]) & mod_q_mask;
 			if (t1[i] >= (this->params->q / 2))
 			{
 				t1[i] -= q_mod_p;
 			}
-			Mtrin[i] = (uint8_t)(t1[i] % 3);
+			Mtrin[i] = (uint8_t)(t1[i] % p);
 			if (Mtrin[i] == 1)
 			{
 				++m1;
@@ -252,12 +252,12 @@ METHOD(ntru_private_key_t, decrypt, bool,
 	{
 		for (i = 0; i < cmprime_len; i++)
 		{
-			t1[i] = (t2[i] + 3 * t1[i]) & mod_q_mask;
+			t1[i] = (t2[i] + p * t1[i]) & mod_q_mask;
 			if (t1[i] >= (this->params->q / 2))
 			{
 				t1[i] -= q_mod_p;
 			}
-			Mtrin[i] = (uint8_t)(t1[i] % 3);
+			Mtrin[i] = (uint8_t)(t1[i] % p);
 		}
 	}
 
@@ -321,9 +321,9 @@ METHOD(ntru_private_key_t, decrypt, bool,
 	for (i = 0; i < cmprime_len; i++)
 	{
 		Mtrin[i] -=  mask_trits[i];
-		if (Mtrin[i] >= 3)
+		if (Mtrin[i] >= p)
 		{
-			Mtrin[i] += 3;
+			Mtrin[i] += p;
 		}
 	}
 	mask->destroy(mask);
@@ -708,7 +708,7 @@ ntru_private_key_t *ntru_private_key_create(ntru_drbg_t *drbg,
 	/* form f = 1 + pF */
 	for (i = 0; i < params->N; i++)
 	{
-		t1[i] = (t1[i] * 3) & mod_q_mask;
+		t1[i] = (p * t1[i]) & mod_q_mask;
 	}
 	t1[0] = (t1[0] + 1) & mod_q_mask;
 
@@ -743,7 +743,7 @@ ntru_private_key_t *ntru_private_key_create(ntru_drbg_t *drbg,
 
 	for (i = 0; i < params->N; i++)
 	{
-		this->pubkey[i] = (t2[i] * 3) & mod_q_mask;
+		this->pubkey[i] = (p * t2[i]) & mod_q_mask;
 	}
 
 	/* cleanup temporary storage */
diff --git a/src/libstrongswan/plugins/ntru/ntru_public_key.c b/src/libstrongswan/plugins/ntru/ntru_public_key.c
index a2ff1b2b04..ac15d2305b 100644
--- a/src/libstrongswan/plugins/ntru/ntru_public_key.c
+++ b/src/libstrongswan/plugins/ntru/ntru_public_key.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2014 Andreas Steffen
+ * Copyright (C) 2014-2015 Andreas Steffen
  * HSR Hochschule fuer Technik Rapperswil
  *
  * Copyright (C) 2009-2013  Security Innovation
@@ -233,9 +233,9 @@ METHOD(ntru_public_key_t, encrypt, bool,
 			for (i = 0; i < mprime_len; i++)
 			{
 				t2[i] = mask_trits[i] + Mtrin[i];
-				if (t2[i] >= 3)
+				if (t2[i] >= p)
 				{
-					t2[i] -= 3;
+					t2[i] -= p;
 				}
 				if (t2[i] == 1)
 				{
@@ -252,9 +252,9 @@ METHOD(ntru_public_key_t, encrypt, bool,
 			for (i = 0; i < mprime_len; i++)
 			{
 				t2[i] = mask_trits[i] + Mtrin[i];
-				if (t2[i] >= 3)
+				if (t2[i] >= p)
 				{
-					t2[i] -= 3;
+					t2[i] -= p;
 				}
 			}
 		}