From: divverent <divverent@d7cf8633-e32d-0410-b094-e92efae38249>
Date: Fri, 11 Oct 2013 14:43:19 +0000 (+0000)
Subject: Netconn: when an encrypted connection is used, randomly set one or more of three... 
X-Git-Tag: xonotic-v0.8.0~114
X-Git-Url: https://git.rm.cloudns.org/?a=commitdiff_plain;h=1453df184bb25502bd90cf441ffcb3182c569f02;p=xonotic%2Fdarkplaces.git

Netconn: when an encrypted connection is used, randomly set one or more of three unused NETFLAGs.

When AES encryption is enabled, this will then work around substring
matching in routers/IPS thanks to CBC and our method of IV selection.
See "startkeylogger". Note that this neither improves nor weakens
security - SSL e.g. has the very issue we're fixing here because it is
based on TCP, and thus resends always are identical payloads.

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@12023 d7cf8633-e32d-0410-b094-e92efae38249
::stable-branch::merge=d153dbd355a89226bca145dffa6a0d024b5ac8a7
---

diff --git a/netconn.c b/netconn.c
index f971fd24..32112da9 100755
--- a/netconn.c
+++ b/netconn.c
@@ -706,6 +706,27 @@ void NetConn_UpdateCleartime(double *cleartime, int rate, int burstsize, int len
 	}
 }
 
+static int NetConn_AddCryptoFlag(crypto_t *crypto)
+{
+	// HACK: if an encrypted connection is used, randomly set some unused
+	// flags. When AES encryption is enabled, that will make resends differ
+	// from the original, so that e.g. substring filters in a router/IPS
+	// are unlikely to match a second time. See also "startkeylogger".
+	int flag = 0;
+	if (crypto->authenticated)
+	{
+		// Let's always set at least one of the bits.
+		int r = rand() % 7 + 1;
+		if (r & 1)
+			flag |= NETFLAG_CRYPTO0;
+		if (r & 2)
+			flag |= NETFLAG_CRYPTO1;
+		if (r & 4)
+			flag |= NETFLAG_CRYPTO2;
+	}
+	return flag;
+}
+
 int NetConn_SendUnreliableMessage(netconn_t *conn, sizebuf_t *data, protocolversion_t protocol, int rate, int burstsize, qboolean quakesignon_suppressreliables)
 {
 	int totallen = 0;
@@ -811,7 +832,7 @@ int NetConn_SendUnreliableMessage(netconn_t *conn, sizebuf_t *data, protocolvers
 
 			packetLen = NET_HEADERSIZE + dataLen;
 
-			StoreBigLong(sendbuffer, packetLen | (NETFLAG_DATA | eom));
+			StoreBigLong(sendbuffer, packetLen | (NETFLAG_DATA | eom | NetConn_AddCryptoFlag(&conn->crypto)));
 			StoreBigLong(sendbuffer + 4, conn->nq.sendSequence - 1);
 			memcpy(sendbuffer + NET_HEADERSIZE, conn->sendMessage, dataLen);
 
@@ -860,7 +881,7 @@ int NetConn_SendUnreliableMessage(netconn_t *conn, sizebuf_t *data, protocolvers
 
 			packetLen = NET_HEADERSIZE + dataLen;
 
-			StoreBigLong(sendbuffer, packetLen | (NETFLAG_DATA | eom));
+			StoreBigLong(sendbuffer, packetLen | (NETFLAG_DATA | eom | NetConn_AddCryptoFlag(&conn->crypto)));
 			StoreBigLong(sendbuffer + 4, conn->nq.sendSequence);
 			memcpy(sendbuffer + NET_HEADERSIZE, conn->sendMessage, dataLen);
 
@@ -890,7 +911,7 @@ int NetConn_SendUnreliableMessage(netconn_t *conn, sizebuf_t *data, protocolvers
 				return -1;
 			}
 
-			StoreBigLong(sendbuffer, packetLen | NETFLAG_UNRELIABLE);
+			StoreBigLong(sendbuffer, packetLen | NETFLAG_UNRELIABLE | NetConn_AddCryptoFlag(&conn->crypto));
 			StoreBigLong(sendbuffer + 4, conn->outgoing_unreliable_sequence);
 			memcpy(sendbuffer + NET_HEADERSIZE, data->data, data->cursize);
 
@@ -1395,7 +1416,7 @@ static int NetConn_ReceivedMessage(netconn_t *conn, const unsigned char *data, s
 
 							packetLen = NET_HEADERSIZE + dataLen;
 
-							StoreBigLong(sendbuffer, packetLen | (NETFLAG_DATA | eom));
+							StoreBigLong(sendbuffer, packetLen | (NETFLAG_DATA | eom | NetConn_AddCryptoFlag(&conn->crypto)));
 							StoreBigLong(sendbuffer + 4, conn->nq.sendSequence);
 							memcpy(sendbuffer + NET_HEADERSIZE, conn->sendMessage, dataLen);
 
@@ -1426,7 +1447,7 @@ static int NetConn_ReceivedMessage(netconn_t *conn, const unsigned char *data, s
 
 				conn->outgoing_netgraph[conn->outgoing_packetcounter].ackbytes        += 8 + 28;
 
-				StoreBigLong(temppacket, 8 | NETFLAG_ACK);
+				StoreBigLong(temppacket, 8 | NETFLAG_ACK | NetConn_AddCryptoFlag(&conn->crypto));
 				StoreBigLong(temppacket + 4, sequence);
 				sendme = Crypto_EncryptPacket(&conn->crypto, temppacket, 8, &cryptosendbuffer, &sendmelen, sizeof(cryptosendbuffer));
 				if(sendme)
diff --git a/netconn.h b/netconn.h
index e9e4ddac..fc13054f 100755
--- a/netconn.h
+++ b/netconn.h
@@ -27,14 +27,16 @@ Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 #define NET_HEADERSIZE		(2 * sizeof(unsigned int))
 
 // NetHeader flags
-#define NETFLAG_LENGTH_MASK	0x0000ffff
-#define NETFLAG_DATA		0x00010000
-#define NETFLAG_ACK			0x00020000
-#define NETFLAG_NAK			0x00040000
-#define NETFLAG_EOM			0x00080000
-#define NETFLAG_UNRELIABLE	0x00100000
-#define NETFLAG_CTL			0x80000000
-#define NETFLAG_CRYPTO		0x40000000
+#define NETFLAG_LENGTH_MASK 0x0000ffff
+#define NETFLAG_DATA        0x00010000
+#define NETFLAG_ACK         0x00020000
+#define NETFLAG_NAK         0x00040000
+#define NETFLAG_EOM         0x00080000
+#define NETFLAG_UNRELIABLE  0x00100000
+#define NETFLAG_CRYPTO0     0x10000000
+#define NETFLAG_CRYPTO1     0x20000000
+#define NETFLAG_CRYPTO2     0x40000000
+#define NETFLAG_CTL         0x80000000
 
 
 #define NET_PROTOCOL_VERSION	3