Polish up passphrase prompts for key decryption.

Now Windows Pageant has two clearly distinct dialog boxes for
requesting a key passphrase: one to use synchronously when the user
has just used the 'Add Key' GUI action, and one to use asynchronously
in response to an agent client's attempt to use a key that was loaded
encrypted.

Also fixed the wording in the asynchronous box: there were two copies
of the 'enter passphrase' instruction, one from the dialog definition
in pageant.rc file and one from the cross-platform pageant.c. Now
pageant.c doesn't format a whole user-facing message any more: it
leaves that to the platform front end to do it the way it wants.

I've also added a call to SetForegroundWindow, to try to get the
passphrase prompt into the foreground. In my experience this doesn't
actually get it the keyboard focus, which I think is deliberate on
Windows's part and there's nothing I can do about it. But at least the
user should _see_ that the prompt is there, so they can focus it
themself.

pageant.c

@@ -392,11 +392,8 @@ static bool request_passphrase(PageantClient *pc, PageantKey *pk)
     if (!pk->decryption_prompt_active) {
         assert(!gui_request_in_progress);
 
-        strbuf *sb = strbuf_new();
-        strbuf_catf(sb, "Enter passphrase to decrypt key '%s'", pk->comment);
         bool created_dlg = pageant_client_ask_passphrase(
-            pc, &pk->dlgid, sb->s);
-        strbuf_free(sb);
+            pc, &pk->dlgid, pk->comment);
 
         if (!created_dlg)
             return false;
@@ -1525,11 +1522,11 @@ static void pageant_conn_got_response(
 }
 
 static bool pageant_conn_ask_passphrase(
-    PageantClient *pc, PageantClientDialogId *dlgid, const char *msg)
+    PageantClient *pc, PageantClientDialogId *dlgid, const char *comment)
 {
     struct pageant_conn_state *pcs =
         container_of(pc, struct pageant_conn_state, pc);
-    return pageant_listener_client_ask_passphrase(pcs->plc, dlgid, msg);
+    return pageant_listener_client_ask_passphrase(pcs->plc, dlgid, comment);
 }
 
 static const PageantClientVtable pageant_connection_clientvt = {
@@ -1719,7 +1716,7 @@ static void internal_client_got_response(
 }
 
 static bool internal_client_ask_passphrase(
-    PageantClient *pc, PageantClientDialogId *dlgid, const char *msg)
+    PageantClient *pc, PageantClientDialogId *dlgid, const char *comment)
 {
     /* No delaying operations are permitted in this mode */
     return false;

pageant.h

@@ -34,7 +34,7 @@ struct PageantClientVtable {
     void (*got_response)(PageantClient *pc, PageantClientRequestId *reqid,
                          ptrlen response);
     bool (*ask_passphrase)(PageantClient *pc, PageantClientDialogId *dlgid,
-                           const char *msg);
+                           const char *key_comment);
 };
 
 static inline void pageant_client_log_v(
@@ -58,8 +58,8 @@ static inline void pageant_client_got_response(
     PageantClient *pc, PageantClientRequestId *reqid, ptrlen response)
 { pc->vt->got_response(pc, reqid, response); }
 static inline bool pageant_client_ask_passphrase(
-    PageantClient *pc, PageantClientDialogId *dlgid, const char *msg)
-{ return pc->vt->ask_passphrase(pc, dlgid, msg); }
+    PageantClient *pc, PageantClientDialogId *dlgid, const char *comment)
+{ return pc->vt->ask_passphrase(pc, dlgid, comment); }
 
 /* PageantClientRequestId is used to match up responses to the agent
  * requests they refer to. A client may allocate one of these for each
@@ -159,7 +159,8 @@ struct PageantListenerClient {
 struct PageantListenerClientVtable {
     void (*log)(PageantListenerClient *, const char *fmt, va_list ap);
     bool (*ask_passphrase)(PageantListenerClient *pc,
-                           PageantClientDialogId *dlgid, const char *msg);
+                           PageantClientDialogId *dlgid,
+                           const char *key_comment);
 };
 
 static inline void pageant_listener_client_log_v(
@@ -179,8 +180,9 @@ static inline PRINTF_LIKE(2, 3) void pageant_listener_client_log(
     }
 }
 static inline bool pageant_listener_client_ask_passphrase(
-    PageantListenerClient *plc, PageantClientDialogId *dlgid, const char *msg)
-{ return plc->vt->ask_passphrase(plc, dlgid, msg); }
+    PageantListenerClient *plc, PageantClientDialogId *dlgid,
+    const char *comment)
+{ return plc->vt->ask_passphrase(plc, dlgid, comment); }
 
 struct pageant_listen_state;
 struct pageant_listen_state *pageant_listener_new(

unix/uxpgnt.c

@@ -103,24 +103,34 @@ static int make_pipe_to_askpass(const char *msg)
 }
 
 static bool uxpgnt_ask_passphrase(
-    PageantListenerClient *plc, PageantClientDialogId *dlgid, const char *msg)
+    PageantListenerClient *plc, PageantClientDialogId *dlgid,
+    const char *comment)
 {
     struct uxpgnt_client *upc = container_of(plc, struct uxpgnt_client, plc);
 
     assert(!upc->dlgid); /* Pageant core should be serialising requests */
 
+    char *msg = dupprintf(
+        "A client of Pageant wants to use the following encrypted key:\n"
+        "%s\n"
+        "If you intended this, enter the passphrase to decrypt the key.",
+        comment);
+
     switch (upc->prompt_type) {
       case RTPROMPT_UNAVAILABLE:
+        sfree(msg);
         return false;
 
       case RTPROMPT_GUI:
         upc->passphrase_fd = make_pipe_to_askpass(msg);
+        sfree(msg);
         if (upc->passphrase_fd < 0)
             return false; /* something went wrong */
         break;
 
       case RTPROMPT_DEBUG:
         fprintf(upc->logfp, "pageant passphrase request: %s\n", msg);
+        sfree(msg);
         break;
     }
 

windows/pageant.rc

@@ -14,16 +14,29 @@
 
 210 DIALOG DISCARDABLE 0, 0, 140, 60
 STYLE DS_MODALFRAME | WS_POPUP | WS_CAPTION | WS_SYSMENU
-CAPTION "Pageant: Enter Passphrase"
+CAPTION "Pageant: Loading Encrypted Key"
 FONT 8, "MS Shell Dlg"
 BEGIN
-    CTEXT "Enter passphrase for key", 100, 10, 6, 120, 8
+    CTEXT "Enter passphrase to load key", 100, 10, 6, 120, 8
     CTEXT "", 101, 10, 16, 120, 8
     EDITTEXT 102, 10, 26, 120, 12, ES_PASSWORD | ES_AUTOHSCROLL
     DEFPUSHBUTTON "O&K", IDOK, 20, 42, 40, 14
     PUSHBUTTON "&Cancel", IDCANCEL, 80, 42, 40, 14
 END
 
+212 DIALOG DISCARDABLE 0, 0, 250, 70
+STYLE DS_MODALFRAME | WS_POPUP | WS_CAPTION | WS_SYSMENU
+CAPTION "Pageant: Decrypting Stored Key"
+FONT 8, "MS Shell Dlg"
+BEGIN
+    CTEXT "A client of Pageant wants to use the following encrypted key:", 100, 10, 6, 230, 8
+    CTEXT "", 101, 10, 16, 230, 8
+    CTEXT "If you intended this, enter the passphrase to decrypt the key.", 101, 10, 26, 230, 8
+    EDITTEXT 102, 10, 36, 230, 12, ES_PASSWORD | ES_AUTOHSCROLL
+    DEFPUSHBUTTON "O&K", IDOK, 75, 52, 40, 14
+    PUSHBUTTON "&Cancel", IDCANCEL, 135, 52, 40, 14
+END
+
 211 DIALOG DISCARDABLE 0, 0, 450, 211
 STYLE DS_MODALFRAME | WS_POPUP | WS_CAPTION | WS_SYSMENU
 CAPTION "Pageant Key List"

windows/winpgnt.c

@@ -863,7 +863,7 @@ static void wm_copydata_got_response(
 }
 
 static bool ask_passphrase_common(PageantClientDialogId *dlgid,
-                                  const char *msg)
+                                  const char *comment)
 {
     /* Pageant core should be serialising requests, so we never expect
      * a passphrase prompt to exist already at this point */
@@ -873,18 +873,55 @@ static bool ask_passphrase_common(PageantClientDialogId *dlgid,
     pps->modal = false;
     pps->dlgid = dlgid;
     pps->passphrase = NULL;
-    pps->comment = msg;
+    pps->comment = comment;
 
     nonmodal_passphrase_hwnd = CreateDialogParam(
-        hinst, MAKEINTRESOURCE(210), NULL, PassphraseProc, (LPARAM)pps);
+        hinst, MAKEINTRESOURCE(212), NULL, PassphraseProc, (LPARAM)pps);
+
+    /*
+     * Try to put this passphrase prompt into the foreground.
+     *
+     * This will probably not succeed in giving it the actual keyboard
+     * focus, because Windows is quite opposed to applications being
+     * able to suddenly steal the focus on their own initiative.
+     *
+     * That makes sense in a lot of situations, as a defensive
+     * measure. If you were about to type a password or other secret
+     * data into the window you already had focused, and some
+     * malicious app stole the focus, it might manage to trick you
+     * into typing your secrets into _it_ instead.
+     *
+     * In this case it's possible to regard the same defensive measure
+     * as counterproductive, because the effect if we _do_ steal focus
+     * is that you type something into our passphrase prompt that
+     * isn't the passphrase, and we fail to decrypt the key, and no
+     * harm is done. Whereas the effect of the user wrongly _assuming_
+     * the new passphrase prompt has the focus is much worse: now you
+     * type your highly secret passphrase into some other window you
+     * didn't mean to trust with that information - such as the
+     * agent-forwarded PuTTY in which you just ran an ssh command,
+     * which the _whole point_ was to avoid telling your passphrase to!
+     *
+     * On the other hand, I'm sure _every_ application author can come
+     * up with an argument for why they think _they_ should be allowed
+     * to steal the focus. Probably most of them include the claim
+     * that no harm is done if their application receives data
+     * intended for something else, and of course that's not always
+     * true!
+     *
+     * In any case, I don't know of anything I can do about it, or
+     * anything I _should_ do about it if I could. If anyone thinks
+     * they can improve on all this, patches are welcome.
+     */
+    SetForegroundWindow(nonmodal_passphrase_hwnd);
 
     return true;
 }
 
 static bool wm_copydata_ask_passphrase(
-    PageantClient *pc, PageantClientDialogId *dlgid, const char *msg)
+    PageantClient *pc, PageantClientDialogId *dlgid, const char *comment)
 {
-    return ask_passphrase_common(dlgid, msg);
+    return ask_passphrase_common(dlgid, comment);
 }
 
 static const PageantClientVtable wmcpc_vtable = {
@@ -1270,9 +1307,10 @@ void cleanup_exit(int code)
 }
 
 static bool winpgnt_listener_ask_passphrase(
-    PageantListenerClient *plc, PageantClientDialogId *dlgid, const char *msg)
+    PageantListenerClient *plc, PageantClientDialogId *dlgid,
+    const char *comment)
 {
-    return ask_passphrase_common(dlgid, msg);
+    return ask_passphrase_common(dlgid, comment);
 }
 
 struct winpgnt_client {