OpenSSL notes
STARTTLS in qmail
=================
You will need the qmail-tls patch:
http://www.esat.kuleuven.ac.be/~vermeule/qmail/tls.patch
What the patch does, part 1
---------------------------
qmail-smtpd will accept the STARTTLS command. This lets clients speak
SMTP/SSL to the server. Everything up to STARTTLS is unencrypted but
after STARTTLS occurs the session is encrypted.
For this to work you need to make a certificate (RSA has been tested)
for qmail-smtpd. Assuming you have a CA cert in /etc/ssl/certs and
that you have changed to that directory (see README.openssl for more
details), do this:
openssl req -new -nodes -out qmail.csr -keyout qmail.key
./sign.sh qmail.csr
cat qmail.key qmail.crt > ~qmaild/control/servercert.pem
chown qmaild.qmail ~qmaild/control/servercert.pem
chmod 400 ~qmaild/control/servercert.pem
OK what was all that about?
First up we generated a new certificate signing request (and key to go with it)
using openssl req. The -nodes option is used to prevent the certificate blurb
from being encrypted. Next we signed the key and then copied it to the qmail
controls directory.
qmail-smtpd will expect to find a file called servercert.pem containing a
private key and matching certificate (IN THAT ORDER). This is different to
apache and OpenLDAP which require you to specify the key and cert in separate
files. Note that using the cat command as described above will leave you with
a whole bunch of certificate blurb in between the key and certificate (ie
between -----END RSA PRIVATE KEY----- and -----BEGIN CERTIFICATE-----). You
may safely trash this text if you like.
You can test this out by telnetting to port 25 on the mail server and typing
starttls. You should see "220 ready for tls" after which qmail will expect
encoded stuff.
Netscape or some other MUA that supports STARTTLS should also work at this
point.
BIG IMPORTANT WARNING:
STARTTLS won't work if you use fixcrio or some other program that helps
out those broken clients and servers out there that violate the SMTP
specs by not sending CRLF properly. You must choose whether to support
buggy clients or secure clients.
What the patch does, part 2
---------------------------
qmail-remote is also patched, and will attempt to negotiate STARTTLS with
remote servers. For this to work you need a signed cert called clientcert.pem
in the controls directory. Making such a cert is no harder than making the
server cert. You may even choose to just link() the two files if you wish.
openssl req -new -nodes -out qmail.csr -keyout qmail.key
./sign.sh qmail.csr
cat qmail.key qmail.crt > ~qmailr/control/clientcert.pem
chown qmailr.qmail ~qmailr/control/clientcert.pem
chmod 400 ~qmailr/control/clientcert.pem
As with the server cert, you are at liberty to nuke the certificate blurb
plaintext.
Outgoing mail will be ssl tunnelled if possible. Note that it is not an error
if the remote server doesn't support STARTTLS, UNLESS you put its certificate
in a file called fqdn.pem where fqdn is the fqdn of the server in question.
What the patch does, part 3
---------------------------
So far we've got qmail receiving mail over an encrypted channel. This is of
course utterly useless in practical terms because the mail will probably only
be relayed out through an unencrypted link anyway, and even if it isn't it will
probably be read via POP3.
We can, however, do something more useful with this patch. You can also tell
qmail-smtpd to accept mail for relaying when a client connects with a kosher
certificate. We need to do two things. First, append the certificate of the
CA that signed the client's cert to clientca.pem. If you used your own ca.crt
to sign other clientcert.pem files for clients to use when they connect to
your qmail-smtpd, it is sufficient to do this:
cp ca.crt ~qmaild/control/clientca.pem
Otherwise you will have to get the cert from the CA and append it to
clientca.pem.
Secondly, you must add the email address associated with the client's cert to
tlsclients in the control directory. If the client entered the email address
of relaying@domain.com when creating the certificate signing request, you must
add relaying@domain.com to tlsclients.
