+;; XXX: since gpg --list-secret-keys does not return validity of each
+;; key, `mml2015-epg-find-usable-key' defined above is not enough for
+;; secret keys. The function `mml2015-epg-find-usable-secret-key'
+;; below looks at appropriate public keys to check usability.
+(defun mml2015-epg-find-usable-secret-key (context name usage)
+ (let ((secret-keys (epg-list-keys context name t))
+ secret-key)
+ (while (and (not secret-key) secret-keys)
+ (if (mml2015-epg-find-usable-key
+ (epg-list-keys context (epg-sub-key-fingerprint
+ (car (epg-key-sub-key-list
+ (car secret-keys)))))
+ usage)
+ (setq secret-key (car secret-keys)
+ secret-keys nil)
+ (setq secret-keys (cdr secret-keys))))
+ secret-key))
+