[Mew-dist 1109] clear key input events

[Kazu Yamamoto ( 山本和彦 )]

Dir sirs,

We would like to ask you to implement an interface to clear recent key
events which (recent-keys) returns for security reasons. Some Emacs
applications read user's password on the mini buffer with echo-back
canceled. However, executing (recent-keys) tells the password even if
it was not displayed at input time. This is really insecure. 

For convenience, Emacs itself should prepare password-input function
as follows:

(defun read-passwd (prompt)
  (let ((pass)
	(c 0)
	(echo-keystrokes 0)
	(ociea cursor-in-echo-area))
    (unwind-protect
	(progn
	  (setq cursor-in-echo-area 1)
	  (while (and (/= c ?\r) (/= c ?\n) (/= c ?\e) (/= c 7)) ;; ^G
	    (message "%s%s"
		     prompt
		     (make-string (length pass) ?.))
	    (setq c (read-char))
	    (if (char-equal c ?\C-u)
		(setq pass "")
	      (if (and (/= c ?\b) (/= c ?\177))
		  (setq pass (concat pass (char-to-string c)))
		(if (> (length pass) 0)
		    (setq pass (substring pass 0 -1))))))
	  (setq cursor-in-echo-area -1)
	  )
      (setq cursor-in-echo-area ociea)
      nil)
    (message "")
    (sit-for 0)
    (substring pass 0 -1)
    (*** clear recent key events ***)
    ))

Thanks,

--Kazu