EB> You can use gpg with Mutt to encrypt email. If you are running in EB> KDE you can use KMail. I don't know what the GNome email client EB> is. Most clients will support encryption and signing.
Note the subject. OP asked about *web-based* email encryption / signing. -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- | Ilya Martynov (http://martynov.org/) | | GnuPG 1024D/323BDEE6 D7F7 561E 4C1D 8A15 8E80 E4AE BE1A 53EB 323B DEE6 | | AGAVA Software Company (http://www.agava.com/) | -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-