SSL certificate creation
========================

Self-signed SSL certificates
----------------------------

Self-signed SSL certificates are the easiest way to get your SSL server
working. However unless you take some action to prevent it,*this is at the cost
of security*:

 * The first time the client connects to the server, it sees the certificate
   and asks the user whether to trust it. The user of course doesn't really
   bother verifying the certificate's fingerprint, so a man-in-the-middle
   attack can easily bypass all the SSL security, steal the user's password and
   so on.
 * If the client was lucky enough not to get attacked the first time it
   connected, the following connections will be secure as long as the client
   had permanently saved the certificate. Some clients do this, while others
   have to be manually configured to accept the certificate.

The only way to be fully secure is to import the SSL certificate to client's
(or operating system's) list of trusted CA certificates prior to first
connection. See <SSL.CertificateClientImporting.txt> how to do it for different
clients.

Self-signed certificate creation
--------------------------------

Dovecot includes a script to build self-signed SSL certificates using OpenSSL.
In the source distribution this exists in doc/mkcert.sh
[http://dovecot.org/doc/mkcert.sh]. Binary installations usually create the
certificate automatically when installing Dovecot and don't include the script.

The SSL certificate's configuration is taken from doc/dovecot-openssl.cnf
[http://dovecot.org/doc/dovecot-openssl.cnf] file. Modify the file before
running mkcert.sh. Especially important field is the CN (Common Name) field,
which should contain your server's host name. The clients will verify that the
CN matches the connected host name, otherwise they'll say the certificate is
invalid. It's also possible to use wildcards (eg. *.domain.com) in the host
name. They should work with most clients.

By default the certificate is created to '/etc/ssl/certs/dovecot.pem' and the
private key file is created to '/etc/ssl/private/dovecot.pem'. Also by default
the certificate will expire in 365 days. If you wish to change any of these,
modify the mkcert.sh script.

Certificate Authorities
-----------------------

The correct way to use SSL is to have each SSL certificate signed by an
Certificate Authority (CA). The client has a list of trusted Certificate
Authorities, so whenever it sees a new SSL certificate signed by a trusted CA,
it will automatically trust the new certificate without asking the user any
questions.

There are two ways to get a CA signed certificate: buy it, or create your own
CA. The clients have a built-in list of trusted CAs, so buying from one of
those CAs will have the advantage of the certificate working without any client
configuration. If you create your own CA, you'll have to install the CA
certificate to all the clients (see <SSL.CertificateClientImporting.txt>).

There are multiple different tools for managing your own CA. The simplest way
is to use a CA managing tool as gnoMint [http://gnomint.sourceforge.net/] or
TinyCA [http://tinyca.sm-zone.net/]. However, if you need to tailor the
properties of the CA, you always can use OpenSSL, very much customizable, but
however a bit cumbersome.

(This file was created from the wiki on 2017-02-24 04:44)
