gistfile1.el

;; Get the keys under the given registry path via WINDOWS\System32\reg.exe.
;; Only keys with the REG_SZ type will be returned.
(defun reg-keys-with-strings (regpath)
  "read a path in the Windows registry. This probably works for string 
  values only. If the path does not exist, it returns nil. "
  (let* ((reg.exe (concat (getenv "windir") "\\system32\\reg.exe"))
	 (reg (shell-command-to-string (concat reg.exe " query " regpath)))
	 (lines (split-string reg "\n" t " +"))
	 (registry-matching-lines
	  (mapcar
	   (lambda (line)
	     (let ((parts (split-string line " +" t)))
	       (and (= (length parts) 3) (string= (nth 1 parts) "REG_SZ") (nth 0 parts)))) lines)))
    (delq nil registry-matching-lines)))

;; Turn a putty registry key, which looks like "rsa2@22:hostname", into a list
;; of (nil hostname). If we could parse a username here, we could provide
;; it as the first element of the list for use in completion.
(defun format-putty-reg-key (key)
  (list nil (nth 1 (split-string key ":"))))

;; Combine the above to produce hosts for TRAMP completion.
(defun ssh-putty-hosts ()
  (mapcar 'format-putty-reg-key (reg-keys-with-strings "HKCU\\Software\\SimonTatham\\PuTTY\\SshHostKeys")))