Secure your SSL/TLS server

Heartbleed

Recently the Heartbleed bug came to light. It is a bug in the OpenSSL library that causes information to leak from the server. It is an undetectable backdoor that allows to gain the private key of your server. Let’s just say it is VERY important to fix it. Most distros have been very quick to propagate the OpenSSL update, so running your favorite update manager should fix it in no time.

To verify if you have protected, run this command and check for built on to be greater or equal to April 7th, 2014:

$ openssl version -a

OpenSSL 1.0.1e 11 Feb 2013

built on: Mon Apr  7 20:33:19 UTC 2014

platform: debian-amd64

Disable weak ciphers

The way SSL/TLS works is that the client and the server must agree on a cipher to use for encryption. If you were to attack a server, you would obviously use the least secure cipher. To protect against this, simply disable ciphers to be known as weak or those which flaws have been discovered.

I am using this configuration for Apache:

SSLCipherSuite ALL:!ADH:!AECDH:RC4+RSA:+HIGH:+MEDIUM:!LOW:!SSLv2:!EXPORT

For Nginx, see their configuration reference. Since 1.0.5, they are using a sensible default. Otherwise, you can use the same as above.

Do not use a too weak or too strong private key

The private key must never be discovered. Otherwise, anyone could decrypt the content and could perpetrate a MITM attack. If the private key is too weak, it could eventually be guessed given enough data. However, SSL/TLS handshakes are very CPU intensive for both the server and the client. Using a key too long will considerably slow down your website. In most cases, 2048 is perfect.

Test your own server

SSL Labs provides a free test suite that will test your ciphers and for known attacks including BEAST and Heartbleed. This is a must: https://www.ssllabs.com/ssltest/

Further reading

I am not a security expert, I simply happen to have done hosting for quite a time. I suggest you do not take my word blindly and go check this very pertinent paper from SSL Labs.

bcrypt with ircmaxell and how to use it

It is common knowledge that md5 is not secure for password hashing. It is almost worst than plaintext because it may falsly induce the impression of security. People aware of this usually also consider sha1 insecure and straightly go to sha256. Some techniques exist to add further security like adding a salt or hashing multiple times but ultimately the flaw remains: those methods are too quick. If you can hash a password in a fraction of a second, a standard bruteforce can as well. That’s why strong password security involves slow algorithms.

I was aware of all those principles, but @ircmaxell, contributor to PHP, made a video on password hashing with a nice comparison of different hashing functions and it struck me how quickly even a sha512 is computed quickly. Before, I often considered bcrypt as a nice feature to add to a backend but I now realise it is a must.



And be sure to check his blog post with the slides and some other discussion (yes, we have the same blog template).

Now, this is all very cute, but Anthony talks about an easy API coming in PHP 5.5 so it will not be usable anytime soon.

Here are plugins/ways to integrate bcrypt into several platforms:

• Symfony2
• Wordpress
• Drupal

Two good libraries:

• PHPass
• PHP-PasswordLib (5.3+)

But really, it boils down to this: