Index: configure.in
===================================================================
--- configure.in.orig	2006-10-03 17:54:09.000000000 +0100
+++ configure.in	2006-10-30 12:58:33.000000000 +0000
@@ -1529,6 +1529,16 @@
   GTK_EXTRA_CFLAGS="$msnative_struct"
 fi
 
+AC_ARG_ENABLE(display-migration,
+	[AC_HELP_STRING([--enable-display-migration],
+			[include support for GPE_CHANGE_DISPLAY protocol])],
+	enable_migration=yes, enable_migration=no)
+if test "$enable_migration" = "yes"; then
+	AC_DEFINE([ENABLE_MIGRATION], 1, [Define if display migration is enabled])
+	GTK_DEP_LIBS="$GTK_DEP_LIBS -lgcrypt"
+fi
+AM_CONDITIONAL(ENABLE_MIGRATION, test $enable_migration = "yes")
+
 AC_SUBST(GTK_PACKAGES)
 AC_SUBST(GTK_EXTRA_LIBS)
 AC_SUBST(GTK_EXTRA_CFLAGS)
Index: gtk/Makefile.am
===================================================================
--- gtk/Makefile.am.orig	2006-10-02 18:27:53.000000000 +0100
+++ gtk/Makefile.am	2006-10-30 12:59:14.000000000 +0000
@@ -589,6 +589,11 @@
 	gtkwindow-decorate.c    \
 	gtkwindow.c		\
 	$(gtk_clipboard_dnd_c_sources)
+
+if ENABLE_MIGRATION
+gtk_base_c_sources += gtkmigration.c
+endif
+
 gtk_c_sources = $(gtk_base_c_sources)
 gtk_all_c_sources = $(gtk_base_c_sources)
 
Index: gtk/gtkmain.c
===================================================================
--- gtk/gtkmain.c.orig	2006-09-03 06:31:21.000000000 +0100
+++ gtk/gtkmain.c	2006-10-30 12:56:34.000000000 +0000
@@ -507,6 +507,10 @@
   _gtk_accel_map_init ();  
   _gtk_rc_init ();
 
+#ifdef ENABLE_MIGRATION
+  gtk_migration_init ();
+#endif
+
   /* Set the 'initialized' flag.
    */
   gtk_initialized = TRUE;
Index: gtk/gtkmigration.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ gtk/gtkmigration.c	2006-10-30 12:56:34.000000000 +0000
@@ -0,0 +1,529 @@
+/*
+ * Copyright (C) 2003, 2005 Philip Blundell <philb@gnu.org>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <stdlib.h>
+#include <ctype.h>
+#include <libintl.h>
+#include <string.h>
+#include <assert.h>
+
+#include <X11/X.h>
+#include <X11/Xlib.h>
+#include <X11/Xatom.h>
+
+#include <gcrypt.h>
+
+#include "gtk.h"
+#include "gdk.h"
+#include "x11/gdkx.h"
+
+#define _(x) gettext(x)
+
+static GdkAtom string_gdkatom, display_change_gdkatom;
+static GdkAtom rsa_challenge_gdkatom;
+
+#define DISPLAY_CHANGE_SUCCESS			0
+#define DISPLAY_CHANGE_UNABLE_TO_CONNECT	1
+#define DISPLAY_CHANGE_NO_SUCH_SCREEN		2
+#define DISPLAY_CHANGE_AUTHENTICATION_BAD	3
+#define DISPLAY_CHANGE_INDETERMINATE_ERROR	4
+
+static gboolean no_auth;
+
+static GSList *all_widgets;
+
+static gboolean gtk_migration_initialised;
+
+#define CHALLENGE_LEN 64
+
+gchar *gtk_migration_auth_challenge_string;
+
+static unsigned char challenge_bytes[CHALLENGE_LEN];
+static unsigned long challenge_seq;
+
+#define hexbyte(x)  ((x) >= 10 ? (x) + 'a' - 10 : (x) + '0')
+
+struct rsa_key
+{
+  gcry_mpi_t n, e, d, p, q, u;
+};
+
+static gcry_mpi_t
+mpi_from_sexp (gcry_sexp_t r, char *tag)
+{
+  gcry_sexp_t s = gcry_sexp_find_token (r, tag, 0);
+  return gcry_sexp_nth_mpi (s, 1, GCRYMPI_FMT_USG);
+}
+
+static char *
+hex_from_mpi (gcry_mpi_t m)
+{
+  char *buf;
+  gcry_mpi_aprint (GCRYMPI_FMT_HEX, (void *)&buf, NULL, m);
+  return buf;
+}
+
+static void
+gtk_migration_crypt_create_hash (char *display, char *challenge, size_t len, char *result)
+{
+  size_t dlen = strlen (display);
+  gchar *buf = g_malloc (dlen + 1 + len);
+  strcpy (buf, display);
+  memcpy (buf + dlen + 1, challenge, len);
+  gcry_md_hash_buffer (GCRY_MD_SHA1, result, buf, len + dlen + 1);
+  g_free (buf);
+}
+
+static int
+do_encode_md (const unsigned char *digest, size_t digestlen, int algo,
+              unsigned int nbits, gcry_mpi_t *r_val)
+{
+  int nframe = (nbits+7) / 8;
+  unsigned char *frame;
+  int i, n;
+  unsigned char asn[100];
+  size_t asnlen;
+
+  asnlen = sizeof(asn);
+  if (gcry_md_algo_info (algo, GCRYCTL_GET_ASNOID, asn, &asnlen))
+    return -1;
+
+  if (digestlen + asnlen + 4  > nframe )
+    return -1;
+  
+  /* We encode the MD in this way:
+   *
+   *	   0  1 PAD(n bytes)   0  ASN(asnlen bytes)  MD(len bytes)
+   *
+   * PAD consists of FF bytes.
+   */
+  frame = g_malloc (nframe);
+  n = 0;
+  frame[n++] = 0;
+  frame[n++] = 1; /* block type */
+  i = nframe - digestlen - asnlen -3 ;
+  assert ( i > 1 );
+  memset ( frame+n, 0xff, i ); n += i;
+  frame[n++] = 0;
+  memcpy ( frame+n, asn, asnlen ); n += asnlen;
+  memcpy ( frame+n, digest, digestlen ); n += digestlen;
+  assert ( n == nframe );
+      
+  gcry_mpi_scan (r_val, GCRYMPI_FMT_USG, frame, nframe, &nframe);
+  g_free (frame);
+  return 0;
+}
+
+static gboolean
+gtk_migration_crypt_check_signature (struct rsa_key *k, char *hash, char *sigbuf)
+{
+  gcry_mpi_t mpi, mpi2;
+  gcry_sexp_t data, sig, key;
+  int rc;
+
+  do_encode_md (hash, 20, GCRY_MD_SHA1, 1024, &mpi);
+
+  gcry_sexp_build (&data, NULL, "(data (value %m))", mpi);
+  
+  gcry_mpi_release (mpi);
+
+  gcry_sexp_build (&key, NULL, "(public-key (rsa (n %m) (e %m)))", k->n, k->e);
+
+  if (gcry_mpi_scan (&mpi2, GCRYMPI_FMT_HEX, sigbuf, 0, NULL))
+    {
+      gcry_sexp_release (data);
+      return FALSE;
+    }
+
+  gcry_sexp_build (&sig, NULL, "(sig-val (rsa (s %m)))", mpi2);
+
+  rc = gcry_pk_verify (sig, data, key);
+
+  gcry_sexp_release (data);
+  gcry_sexp_release (key);
+  gcry_sexp_release (sig);
+  gcry_mpi_release (mpi2);
+
+  if (rc)
+    return FALSE;
+
+  return TRUE;
+}
+
+static void 
+gtk_migration_auth_update_challenge (void)
+{
+  int i;
+  unsigned char *p;
+
+  if (gtk_migration_auth_challenge_string == NULL)
+    gtk_migration_auth_challenge_string = g_malloc ((CHALLENGE_LEN * 2) + 9);
+
+  p = gtk_migration_auth_challenge_string;
+
+  for (i = 0; i < CHALLENGE_LEN; i++)
+    {
+      *p++ = hexbyte (challenge_bytes[i] >> 4);
+      *p++ = hexbyte (challenge_bytes[i] & 15);
+    }
+  
+  sprintf (p, "%08lx", challenge_seq++);
+}
+
+static void
+gtk_migration_auth_generate_challenge (void)
+{
+  gcry_randomize (challenge_bytes, sizeof (challenge_bytes), GCRY_STRONG_RANDOM);
+  gtk_migration_auth_update_challenge ();
+}
+
+static struct rsa_key *
+parse_pubkey (char *s)
+{
+  struct rsa_key *r;
+  gcry_mpi_t n, e;
+  gchar *sp;
+
+  sp = strtok (s, " \n");
+  gcry_mpi_scan (&e, GCRYMPI_FMT_HEX, sp, 0, NULL);
+  sp = strtok (NULL, " \n");
+  gcry_mpi_scan (&n, GCRYMPI_FMT_HEX, sp, 0, NULL);
+
+  r = g_malloc0 (sizeof (struct rsa_key));
+  r->e = e;
+  r->n = n;
+  return r;
+}
+
+static struct rsa_key *
+lookup_pubkey (u_int32_t id)
+{
+  const gchar *home_dir = g_get_home_dir ();
+  gchar *filename = g_strdup_printf ("%s/.gpe/migrate/public", home_dir);
+  FILE *fp = fopen (filename, "r");
+  struct rsa_key *r = NULL;
+
+  if (fp)
+    {
+      while (!feof (fp))
+	{
+	  char buffer[4096];
+	  if (fgets (buffer, 4096, fp))
+	    {
+	      char *p;
+	      u_int32_t this_id = strtoul (buffer, &p, 16);
+	      if (p != buffer && *p == ' ')
+		{
+#ifdef DEBUG
+		  fprintf (stderr, "found id %x\n", this_id);
+#endif
+		  if (this_id == id)
+		    {
+		      r = parse_pubkey (++p);
+		      break;
+		    }
+		}
+	    }
+	}
+      fclose (fp);
+    }
+
+  g_free (filename);
+  return r;
+}
+
+static void
+free_pubkey (struct rsa_key *k)
+{
+  gcry_mpi_release (k->n);
+  gcry_mpi_release (k->e);
+
+  g_free (k);
+}
+
+static gboolean
+gtk_migration_auth_validate_request (char *display, char *data)
+{
+  u_int32_t key_id;
+  char *ep;
+  char *p;
+  struct rsa_key *k;
+  char hash[20];
+  gboolean rc;
+
+  p = strchr (data, ' ');
+  if (p == NULL)
+    return FALSE;
+  *p++ = 0;
+
+  key_id = strtoul (data, &ep, 16);
+  if (*ep)
+    return FALSE;
+
+  k = lookup_pubkey (key_id);
+  if (k == NULL)
+    return FALSE;
+
+  gtk_migration_crypt_create_hash (display, gtk_migration_auth_challenge_string, 
+			   strlen (gtk_migration_auth_challenge_string), hash);
+
+  rc = gtk_migration_crypt_check_signature (k, hash, p);
+
+  free_pubkey (k);
+
+  return rc;
+}
+
+static int
+do_change_display (GtkWidget *w, char *display_name)
+{
+  GdkDisplay *newdisplay;
+  guint screen_nr = 1;
+  guint i;
+
+  if (display_name[0] == 0)
+    return DISPLAY_CHANGE_INDETERMINATE_ERROR;
+
+  i = strlen (display_name) - 1;
+  while (i > 0 && isdigit (display_name[i]))
+    i--;
+
+  if (display_name[i] == '.')
+    {
+      screen_nr = atoi (display_name + i + 1);
+      display_name[i] = 0;
+    }
+
+  newdisplay = gdk_display_open (display_name);
+  if (newdisplay)
+    {
+      GdkScreen *screen = gdk_display_get_screen (newdisplay, screen_nr);
+      if (screen)
+	{
+	  gtk_window_set_screen (GTK_WINDOW (w), screen);
+	  gdk_display_manager_set_default_display (gdk_display_manager_get (),
+						   newdisplay);
+	  return DISPLAY_CHANGE_SUCCESS;
+	}
+      else
+	return DISPLAY_CHANGE_NO_SUCH_SCREEN;
+    }
+
+  return DISPLAY_CHANGE_UNABLE_TO_CONNECT;
+}
+
+static void
+set_challenge_on_window (GdkWindow *window)
+{
+  gdk_property_change (window, rsa_challenge_gdkatom, string_gdkatom,
+		       8, GDK_PROP_MODE_REPLACE, gtk_migration_auth_challenge_string, 
+		       strlen (gtk_migration_auth_challenge_string));
+}
+
+static void
+update_challenge_on_windows (void)
+{
+  GSList *i;
+
+  gtk_migration_auth_update_challenge ();
+
+  for (i = all_widgets; i; i = i->next)
+    {
+      GtkWidget *w = GTK_WIDGET (i->data);
+      if (w->window)
+	set_challenge_on_window (w->window);
+    }
+}
+
+static void
+reset_state (GdkWindow *window)
+{
+  gdk_property_change (window, display_change_gdkatom, string_gdkatom,
+		       8, GDK_PROP_MODE_REPLACE, NULL, 0);
+}
+
+static void
+generate_response (GdkDisplay *gdisplay, Display *dpy, Window window, int code)
+{
+  XClientMessageEvent ev;
+  Atom atom = gdk_x11_atom_to_xatom_for_display (gdisplay, 
+						 display_change_gdkatom);
+  
+  memset (&ev, 0, sizeof (ev));
+  
+  ev.type = ClientMessage;
+  ev.window = window;
+  ev.message_type = atom;
+  ev.format = 32;
+  
+  ev.data.l[0] = window;
+  ev.data.l[1] = code;
+  
+  XSendEvent (dpy, DefaultRootWindow (dpy), False, SubstructureNotifyMask, (XEvent *)&ev);
+}
+
+static int
+handle_request (GdkWindow *gwindow, char *prop)
+{
+  GtkWidget *widget;
+  char *target, *auth_method, *auth_data;
+  char *p;
+
+  target = prop;
+  auth_method = "NULL";
+  auth_data = NULL;
+
+  p = strchr (prop, ' ');
+  if (p)
+    {
+      *p = 0;
+      auth_method = ++p;
+      
+      p = strchr (p, ' ');
+      if (p)
+	{
+	  *p = 0;
+	  auth_data = ++p;
+	}
+    }
+
+  if (no_auth == FALSE)
+    {
+      if (!strcasecmp (auth_method, "null"))
+	return DISPLAY_CHANGE_AUTHENTICATION_BAD;
+      else if (!strcasecmp (auth_method, "rsa-sig"))
+	{
+	  if (gtk_migration_auth_validate_request (target, auth_data) == FALSE)
+	    return DISPLAY_CHANGE_AUTHENTICATION_BAD;
+	}
+      else
+	return DISPLAY_CHANGE_AUTHENTICATION_BAD;
+    }
+
+  gdk_window_get_user_data (gwindow, (gpointer*) &widget);
+
+  if (widget)
+    return do_change_display (widget, target);
+
+  return DISPLAY_CHANGE_INDETERMINATE_ERROR;
+}
+
+static GdkFilterReturn 
+filter_func (GdkXEvent *xevp, GdkEvent *ev, gpointer p)
+{
+  XPropertyEvent *xev = (XPropertyEvent *)xevp;
+
+  if (xev->type == PropertyNotify)
+    {
+      GdkDisplay *gdisplay;
+      Atom atom;
+
+      gdisplay = gdk_x11_lookup_xdisplay (xev->display);
+      if (gdisplay)
+	{
+	  atom = gdk_x11_atom_to_xatom_for_display (gdisplay, display_change_gdkatom);
+
+	  if (xev->atom == atom)
+	    {
+	      GdkWindow *gwindow;
+	      
+	      gwindow = gdk_window_lookup_for_display (gdisplay, xev->window);
+	      
+	      if (gwindow)
+		{
+		  GdkAtom actual_type;
+		  gint actual_format;
+		  gint actual_length;
+		  unsigned char *prop = NULL;
+		  
+		  if (gdk_property_get (gwindow, display_change_gdkatom, string_gdkatom,
+					0, G_MAXLONG, FALSE, &actual_type, &actual_format,
+					&actual_length, &prop))
+		    {
+		      if (actual_length != 0)
+			{
+			  if (actual_type == string_gdkatom && actual_length > 8)
+			    {
+			      gchar *buf = g_malloc (actual_length + 1);
+			      int rc;
+			      
+			      memcpy (buf, prop, actual_length);
+			      buf[actual_length] = 0;
+			      
+			      rc = handle_request (gwindow, buf);
+			      
+			      g_free (buf);
+			      generate_response (gdisplay, xev->display, xev->window, rc);
+			      
+			      if (rc == DISPLAY_CHANGE_SUCCESS)
+				update_challenge_on_windows ();
+			    }
+			  
+			  reset_state (gwindow);
+			}
+		    }
+		  
+		  if (prop)
+		    g_free (prop);
+		}
+	    }
+	  
+	  return GDK_FILTER_REMOVE;
+	}
+    }
+
+  return GDK_FILTER_CONTINUE;
+}
+
+static void
+unrealize_window (GtkWidget *w)
+{
+  all_widgets = g_slist_remove (all_widgets, w);
+}
+
+void
+gtk_migration_mark_window (GtkWidget *w)
+{
+  if (! gtk_migration_initialised)
+    {
+      g_warning ("gtk_migration not initialised yet");
+      return;
+    }
+
+  if (GTK_WIDGET_REALIZED (w))
+    {
+      GdkWindow *window = w->window;
+      
+      gdk_window_add_filter (window, filter_func, NULL);
+
+      reset_state (window);
+      set_challenge_on_window (window);
+
+      all_widgets = g_slist_append (all_widgets, w);
+
+      g_signal_connect (G_OBJECT (w), "unrealize", G_CALLBACK (unrealize_window), NULL);
+    }
+  else
+    g_signal_connect (G_OBJECT (w), "realize", G_CALLBACK (gtk_migration_mark_window), NULL);
+}
+
+void
+gtk_migration_init (void)
+{
+  if (getenv ("GPE_DISPLAY_MIGRATION_NO_AUTH") != NULL)
+    no_auth = TRUE;
+
+  string_gdkatom = gdk_atom_intern ("STRING", FALSE);
+  display_change_gdkatom = gdk_atom_intern ("_GPE_DISPLAY_CHANGE", FALSE);
+  rsa_challenge_gdkatom = gdk_atom_intern ("_GPE_DISPLAY_CHANGE_RSA_CHALLENGE", FALSE);
+
+  gtk_migration_auth_generate_challenge ();
+
+  gtk_migration_initialised = TRUE;
+}
Index: gtk/gtkwindow.c
===================================================================
--- gtk/gtkwindow.c.orig	2006-10-03 16:51:46.000000000 +0100
+++ gtk/gtkwindow.c	2006-10-30 12:56:34.000000000 +0000
@@ -50,6 +50,9 @@
 #include "x11/gdkx.h"
 #endif
 
+extern void gtk_migration_mark_window (GtkWidget *w);
+                                                               
+
 enum {
   SET_FOCUS,
   FRAME_EVENT,
@@ -823,6 +826,10 @@
 
   g_signal_connect (window->screen, "composited_changed",
 		    G_CALLBACK (gtk_window_on_composited_changed), window);
+		    
+#ifdef ENABLE_MIGRATION
+  gtk_migration_mark_window (window);
+#endif
 }
 
 static void