/contrib/famzah

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Enable Forward Secrecy in Apache 2.4

The Heartbleed bug once again raised a very serious question — what happens if someone steals our SSL private key. The future actions are all clear — we revoke the key, change it on the server and we are secure. However any recorded past SSL encrypted sessions which the attacker posses can be decrypted to plain text using the stolen SSL private key.

The article “SSL: Intercepted today, decrypted tomorrow” explains the problem in great details. It also suggests who may take advantage of your stolen SSL private key.

Fortunately there is a solution to this attack vector. It is called Forward Secrecy and solves the problem by using a different private key to encrypt each new SSL session. If an attacker wanted to decrypt all your SSL sessions, the attacker would need to brute-force the private keys of each of your SSL sessions. While this attack vector still exists, current computing power is too small to solve such a task in a reasonable time. Note that Forward Secrecy is not new at all and was invented in 1992, pre-dating the SSL protocol by two years, as stated in the “SSL: Intercepted today, decrypted tomorrow” article.

Many websites and blogs recommend their own cipher list which needs to be used, in order to enable Perfect Secrecy, and at the same time to not be vulnerable to the BEAST attack. Trusting such long lists of ciphers without understanding all of them makes me a bit insecure. Luckily the OpenSSL vendors have created a special string which we can use to identify the TLS v1.2 specific ciphers — “TLSv1.2”. This makes your Apache configuration very readable and leaves the control in the OpenSSL developers who can update the ciphers accordingly:

SSLProtocol -ALL -SSLv2 +SSLv3 +TLSv1 +TLSv1.1 +TLSv1.2
SSLHonorCipherOrder on
SSLCipherSuite TLSv1.2:RC4:HIGH:!aNULL:!eNULL:!MD5
SSLCompression off

TraceEnable Off

The effect of this configuration is that for TLS v1.2 connections you will prefer the strong TLS v1.2 ciphers. For all other connections, like SSLv3 or TLS v1.0, the RC4 ciphers will be used which are required to protect against the BEAST attack. Note that TLS v1.2 does not suffer from the BEAST attack.

This configuration won’t give you Forward Secrecy for Internet Explorer. The explanation here says:
“Internet Explorer, in all versions, does not support the ECDHE and RC4 combination (which has the benefit of supporting Forward Secrecy and being resistant to BEAST). But IE has long patched the BEAST vulnerability and so we shouldn’t worry about it.”

It’s worth mentioning that using those strong TLS v1.2 ciphers may increase the CPU time required to establish a new SSL connection 3 times.


Real-time SSL test:

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Free SSL certificates

More and more people start telling me about the StartSSL SSL authority, which is a daughter company of StartCom. The rumor that they are giving free SSL certificates looked too unbelievable to me, so I decided to review this more carefully.

After much reading at their page, what people say was confirmed – StartSSL really issue SSL certificates for free, when they are about to be used by individuals on their websites. This means that your personal name stays in the SSL certificate information which can be reviewed if you click on the SSL bar in your web browser.

Business or other legal entities verify their company’s information once for an annual fee and can then issue an unlimited count of SSL certificates too, including wild-card ones. Once verified, a business customer can purchase EV certificates for US$ 49.90 per year.

You can compare these prices with any other SSL certificate authority and you’ll see it yourself that StartSSL are the most affordable one, and the only one which doesn’t charge you for what doesn’t cost them money either – that’s why they can offer “loosely verified” SSL certificates for personal websites for free. It’s unbelievable but true.

My IT brain immediately started to doubt the technical side. I had to check if web browsers accept these SSL certificates without issuing an SSL warning about the certificate being signed by an unknown SSL authority. The test results were successful and the SSL root authority of StartSSL was recognized by the latest version of:

  • Internet Explorer 8 on Windows.
  • Chrome on Windows.
  • Firefox on Windows and Linux.
  • Chromium on Linux.

Furthermore, the Debian “lenny”, “squeeze” and Ubuntu Lucid CA repositories also recognize the StartSSL root certificate. You can verify this yourself by the following command:
openssl s_client -CApath /etc/ssl/certs -connect startssl.com:443

StartSSL have a long list with platforms and browsers which recognize their certificates. You can review the list at the products comparison page.

No more self-signed SSL certificates for personal use, hurray! 🙂

Update 29/Nov/2010: If you’re interested, you can also review my success story with the Support staff of StartSSL.