GnuPG: www.gnupg.org
RFC 2440: www.rfc-editor.org/rfc/rfc2440.txt
Philip Zimmermann: www.philzimmermann.com
Diceware Passphrase Home Page: www.diceware.com
Wikipedia: Passphrase Article: www.wikipedia.org/wiki/Passphrase
GnuPG HOWTOs: www.gnupg.org/documentation/howtos.html