Various tools to assess SSL resistance to DoS

• server-vs-client measures the computational difference between server and client. It needs a cipher suite (from openssl ciphers) and an appropriate certificate for the server side. Test it with RSA, DH, DSS, ECDH, ECDSA. If it is not able to do any handshake, you need to check if your certificate is compatible with the given cipher suite. Check with openssl s_client and openssl s_server.

• iptables.sh is a set of iptables rule to help avoid SSL DoS. Note that those rules rely heavily on heuristics. It is possible to evade them and they can flag false positives. Be cautious.

• brute-shake will do a lot of parallel handshakes against a server without doing any crypto operation (while the server will do a lot of them). Because it could be abused to take down a SSL server, it will only uses NULL-MD5 cipher suite. No serious SSL server will accept this kind of cipher suite.

You can find more information in this article: http://vincent.bernat.im/en/blog/2011-ssl-dos-mitigation.html