Dovecot: Missing dh.pem

Yesterday, I upgraded my mail server’s operating system. After upgrading, I encountered the following error in dovecot:

config: Warning: please set ssl_dh=</etc/dovecot/dh.pem

What’s dh.pem? I found the answer in the Dovecot 2.3 upgrade documentation. Apparently, the ssl-parameters.dat file is now obsolete. You should use ssl_dh setting instead by adding: ssl_dh=</etc/dovecot/dh.pem to the configuration.

But how do you get dh.pem?

One way is to can convert an existing/old ssl-parameters.dat to dh.pem:

dd if=/var/lib/dovecot/ssl-parameters.dat bs=1 skip=88 | openssl dhparam -inform der > /etc/dovecot/dh.pem

Another way, which I found here, is to generate a new dh.pem:

openssl dhparam -out /etc/dovecot/dh.pem 4096 -days 3650

It takes a LOOONG time. But once the file is ready, just add it to /etc/dovecot/conf.d/10-ssl.conf

ssl_cert = </etc/letsencrypt/live/myserver.xyz/fullchain.pem
ssl_key = </etc/letsencrypt/live/myserver.xyz/privkey.pem
ssl_dh = </etc/dovecot/dh.pem

Restart dovecot and you’re back in business.

Enable HTTPS On Your Website With Let’s Encrypt

There’s no question that secure communications is critical. On the web, this is done using HTTPS. HTTPS is secure extension of the HTTP. In HTTPS, communications is encrypted using Transport Layer Security (TLS), or its deprecated predecessor, Secure Sockets Layer (SSL).

TLS uses a public key encryption scheme where you have a public and private key pair. The web server provides they public key which the web browser can use to encrypt communications with. The public key is signed to certify the identity of the web server owning the key. This gives you the public key certificate or just simply certificate.

You can self-sign (or self-certify) just so you can encrypt communications and that’s fine if your dealing with yourself or parties who trust you and your self-signed certificate (e.g. your own systems or employees). But if you deal with other parties (e.g. other systems or customers) you need a certificate from a certificate authority (CA), a trusted entity that signs keys and issues certificates. 

Let’s Encrypt is a free, automated, and open certificate authority brought to you by the non-profit Internet Security Research Group (ISRG). They provide certificates absolutely free. The certificates expire in 90 days, but they can be automatically renewed using Certbot. There’s simply no excuse not to have a secure site. And it’s so easy to boot. There are step-by-step instructions for almost every web server and operating system combination at the Certbot page.

Here are the steps for getting certificates using Ubuntu and Apache:

  1. Add the Certbot apt repository
    • sudo add-apt-repository ppa:certbot/certbot
    •  
  2. Update the repository
    • sudo apt-get update
  3. Install Certbot from the new repository with apt-get:
    • sudo apt-get install python-certbot-apache
    •  
  4. Obtain a certificate for your domain

This give your certificates for your new files and configures Apache automatically. But you should be able to find the certificate files for other purposes (see below) at /etc/letsencrypt/live/example.com

The certificate only last for 90 days. However, Certbot takes care of this problem by running certbot renew twice a day via a systemd timer or cron. We can also manually test renewal:

  • sudo certbot renew –dry-run

BONUS: If you’re using Dovecot https://www.dovecot.org/, you can also use the certificate:

  1. Edit /etc/dovecot/conf.d/10-ssl.conf:
    • ssl_cert = /etc/letsencrypt/live/example.com/fullchain.pem
    • ssl_key = /etc/letsencrypt/live/example.com/privkey.pem
  2. Restart dovecot:
    • sudo service dovecot restart

That’s it! You now have a secure website and email server.

Setting Up Subversion

Every developer should have version control. It can be a simple process or a process supported by tools. One of the best version  control tools is Subversion or SVN. Here’s how to set up your own SVN server on a Linux box.

Install or update Subversion: If you’re using Red Hat-type Linux: yum install subversion or yum update subversion. If you’re using Debian-type Linux: apt-get install subversion or apt-get update subversion. Others Linux flavors should have something similar.

Create your repository: svnadmin create /svnroot

Configure access: vi /svnroot/conf/svnserve.conf. In the [general] section, add:

anon-access = none
auth-access = write
password-db = passwd

Add users: vi /svnroot/conf/passwd and add:

<username> = <password>

Start Subversion as a daemon: svnserve -d.

Open up TCP port 3690 on your Linux box’s firewall.

Connect to your SVN server with the URL svn://<server name or ip>>/svnroot

Start using your SVN server. Here are some useful tips:

  1. How to structure your repository
  2. How to fix bugs properly
  3. How to release software properly

That’s it!

Skype on Linux

My sister needed a computer for reviewing for her medical exams so I lent her my old (ancient?) IBM Thinkpad X22 which is running Kubuntu. She needed Skype to be able to talk to her hubby who is in the US so we downloaded and installed Skype. Well, what do you know? It actually installed and ran without a hitch. Linux definitely has come a long way. If it we’re not for my games, I would have it on my Asus EEE PC 1000H. I wonder if it’s time to check out Wine, the Linux Windows Emulator, again. Hmmm.