How to use Emacs to recognize and automatically open GPG encrypted file in ASCII armored format?

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http://unix.stackexchange.com – gpg -ca passwords.txt create encrypted ASCII file passwords.txt.asc. Emacs open the file as a normal text file: -----BEGIN PGP MESSAGE----- Version: GnuPG v2.0.19 (GNU/Linux) jA0EAwMCkIp3+bQkLWJgyTQYLGVN8EUEG0BE42sEj/8PrnSzgviSiENxtK+/2n73 WXD7EtndVS/MX4lFJ96h8VozChUA =zSwh -----END PGP MESSAGE----- How do I make Emacs auto-decrypt and encrypt the file when I open and save it? All the files end with .gpg. (HowTos)