SSL
===

SSL and TLS terms are often used in confusing ways:

 * SSL (Secure Sockets Layer) is the original protocol implementation. SSLv3 is
   still allowed by Dovecot, but it's rarely used. Some clients use SSL to mean
   that they're going to connect to the imaps (993), pop3s (995) or smtps (465)
   port, although they're still going to use TLSv1 protocol.
 * TLS (Transport Layer Security) replaced the SSL protocol. TLSv1 protocol is
   used practically always nowadays. Some clients use TLS to mean that they're
   going to use STARTTLS command after connecting to the standard imap (143),
   pop3 (110) or smtp port (25/587). Nothing would prevent using SSLv3 protocol
   after STARTTLS command.

Using two separate ports for plaintext and SSL connections was thought to be
wasteful, so STARTTLS intended to deprecate the SSL ports (imaps, pop3s, smtps,
etc). This never really happened, probably because of two reasons:

 * Some admins don't even know about STARTTLS.
 * Some admins want to require SSL/TLS, but don't realize that this is also
   possible with STARTTLS (Dovecot has 'disable_plaintext_auth=yes' and
   'ssl=required' settings).
 * Some admins understand everything, but still prefer to allow only SSL ports.
   This could be because it makes it easier to ensure that no information is
   leaked, because SSL/TLS handshake happens immediately. Some clients
   unfortunately try to do plaintext authentication without STARTTLS, even when
   IMAP server has told the client that it won't work.

Unfortunately there doesn't seem to be any clear and simple way to refer to
these different meanings.

SSL term is much more widely understood than TLS, so Dovecot configuration and
this documentation only talks about SSL when in fact it means both SSL/TLS.

 * <Creating SSL certificates> [SSL.CertificateCreation.txt]
 * <Configuring Dovecot to use SSL certificates> [SSL.DovecotConfiguration.txt]

 * <Importing CAs and self-signed SSL certificates to clients>
   [SSL.CertificateClientImporting.txt]
 * SSL works pretty much the same universally, so for more information about
   SSL you can see for example Apache's documentation
   [http://httpd.apache.org/docs/2.2/ssl/].
 * Dovecot uses OpenSSL, so whatever information you find about it applies also
   to Dovecot.

(This file was created from the wiki on 2011-05-11 04:42)