SSL Ciphers - Beyond Private key and Certificate

Created on Jul 09 2014, 10:20 AM by Robert Lin

Today SSL is an integral part of online businesses and any secured communication. It is however not an area that many system administrators or security experts are comfortable with. For most administrators the correct installation of the private key and its corresponding certificate is sufficient. As long as the green bar, the padlock, or https:// can be seen during the SSL/TLS negotiation, both the administrators and their clients trust that the connectivity is secure.

However many security flaws and vulnerabilities have been discovered in the recent years. From the server side there is the infamous Heartbleed bug or CCS injection - CVE-2014-0224, side-channel attacks such as Beast, Lucky 13, Crime or BREACH, and others (SSL Attack Survey).  It is not sufficient to just have a correct installation of the private key and certificate pair on the server. Beside patching up server libraries and client applications, additional control to SSL/TLS negotiations need to be applied. One of those control mechanisms is selecting the right cipher suite.

The strength of an SSL/TLS negotiation depends not only the size of the private key or certificate. As of 2014, the recommended minimium key pair size is 2048 bit, however this does not guarantee maximum encryption sessions. During SSL/TLS handshakes, the agreement of what cipher suite to use determines if the negotiation will be using SSL or TLS protocols. It also determines the key exchange and encryption algorithms. If the agreed encryption level between the client and the server is low, the SSL/TLS session will still be vulnerable. For a system to be truly secure, strong cipher suites are required.

To address this issue, a project was initiated. The result, "SSL/ TLS Cipher Suite Analysis and strong Cipher Enablement" is included in this blog.

The purpose of this research is to provide an implementation process to set up a strongly secured SSL/TLS system by viewing the available cipher suites present in a system, recognizing the strength and weakness of the different ciphers and choosing the most applicable cipher suite.

Note:  The configuration examples given in this document do not represent the complete or best set of strong ciphers to use. Depending on the various security policies and business requirements, the examples given in the document may not apply .

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    What keeps the initial key exchanges from being intercepted and used with the public key as well?