Buffer obfuscation

obfuscate-buffer.el

(defvar my-buffer-obfuscation-overlay nil)

(defun my-obfuscate-buffer ()
  (interactive)
  (let* ((buffer-content (buffer-substring (point-min) (point-max))))
    (dotimes (i (length buffer-content))
      (let ((char (aref buffer-content i)))
        (when (string-match-p "[[:graph:]]" (char-to-string char))
          (aset buffer-content i ?.))))
    (setq my-buffer-obfuscation-overlay
          (make-overlay (point-min) (point-max)))
    (overlay-put my-buffer-obfuscation-overlay
                 'display buffer-content)))

(defun my-unobfuscate-buffer ()
  (interactive)
  (when my-buffer-obfuscation-overlay
    (delete-overlay my-buffer-obfuscation-overlay)
    (setq my-buffer-obfuscation-overlay nil)))