diff --git a/clientloop.c b/clientloop.c
index ae4dce8..ee36cc9 100644
--- a/clientloop.c
+++ b/clientloop.c
@@ -59,7 +59,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: clientloop.c,v 1.137 2005/06/08 11:25:09 djm Exp $");
+RCSID("$OpenBSD: clientloop.c,v 1.138 2005/06/16 03:38:36 djm Exp $");
 
 #include "ssh.h"
 #include "ssh1.h"
@@ -208,6 +208,109 @@
 	return (double) tv.tv_sec + (double) tv.tv_usec / 1000000.0;
 }
 
+#define SSH_X11_PROTO "MIT-MAGIC-COOKIE-1"
+void
+client_x11_get_proto(const char *display, const char *xauth_path,
+    u_int trusted, char **_proto, char **_data)
+{
+	char cmd[1024];
+	char line[512];
+	char xdisplay[512];
+	static char proto[512], data[512];
+	FILE *f;
+	int got_data = 0, generated = 0, do_unlink = 0, i;
+	char *xauthdir, *xauthfile;
+	struct stat st;
+
+	xauthdir = xauthfile = NULL;
+	*_proto = proto;
+	*_data = data;
+	proto[0] = data[0] = '\0';
+
+	if (xauth_path == NULL ||(stat(xauth_path, &st) == -1)) {
+		debug("No xauth program.");
+	} else {
+		if (display == NULL) {
+			debug("x11_get_proto: DISPLAY not set");
+			return;
+		}
+		/*
+		 * Handle FamilyLocal case where $DISPLAY does
+		 * not match an authorization entry.  For this we
+		 * just try "xauth list unix:displaynum.screennum".
+		 * XXX: "localhost" match to determine FamilyLocal
+		 *      is not perfect.
+		 */
+		if (strncmp(display, "localhost:", 10) == 0) {
+			snprintf(xdisplay, sizeof(xdisplay), "unix:%s",
+			    display + 10);
+			display = xdisplay;
+		}
+		if (trusted == 0) {
+			xauthdir = xmalloc(MAXPATHLEN);
+			xauthfile = xmalloc(MAXPATHLEN);
+			strlcpy(xauthdir, "/tmp/ssh-XXXXXXXXXX", MAXPATHLEN);
+			if (mkdtemp(xauthdir) != NULL) {
+				do_unlink = 1;
+				snprintf(xauthfile, MAXPATHLEN, "%s/xauthfile",
+				    xauthdir);
+				snprintf(cmd, sizeof(cmd),
+				    "%s -f %s generate %s " SSH_X11_PROTO
+				    " untrusted timeout 1200 2>" _PATH_DEVNULL,
+				    xauth_path, xauthfile, display);
+				debug2("x11_get_proto: %s", cmd);
+				if (system(cmd) == 0)
+					generated = 1;
+			}
+		}
+		snprintf(cmd, sizeof(cmd),
+		    "%s %s%s list %s . 2>" _PATH_DEVNULL,
+		    xauth_path,
+		    generated ? "-f " : "" ,
+		    generated ? xauthfile : "",
+		    display);
+		debug2("x11_get_proto: %s", cmd);
+		f = popen(cmd, "r");
+		if (f && fgets(line, sizeof(line), f) &&
+		    sscanf(line, "%*s %511s %511s", proto, data) == 2)
+			got_data = 1;
+		if (f)
+			pclose(f);
+	}
+
+	if (do_unlink) {
+		unlink(xauthfile);
+		rmdir(xauthdir);
+	}
+	if (xauthdir)
+		xfree(xauthdir);
+	if (xauthfile)
+		xfree(xauthfile);
+
+	/*
+	 * If we didn't get authentication data, just make up some
+	 * data.  The forwarding code will check the validity of the
+	 * response anyway, and substitute this data.  The X11
+	 * server, however, will ignore this fake data and use
+	 * whatever authentication mechanisms it was using otherwise
+	 * for the local connection.
+	 */
+	if (!got_data) {
+		u_int32_t rnd = 0;
+
+		logit("Warning: No xauth data; "
+		    "using fake authentication data for X11 forwarding.");
+		strlcpy(proto, SSH_X11_PROTO, sizeof proto);
+		for (i = 0; i < 16; i++) {
+			if (i % 4 == 0)
+				rnd = arc4random();
+			snprintf(data + 2 * i, sizeof data - 2 * i, "%02x",
+			    rnd & 0xff);
+			rnd >>= 8;
+		}
+	}
+}
+
 /*
  * This is called when the interactive is entered.  This checks if there is
  * an EOF coming on stdin.  We must check this explicitly, as select() does