how to secure the ciphers?

Install this patch. It will fix a problem with SSLConfig/CipherSuites and SSLConfig/Protocols:

WowzaMediaServer3.1.1-patch6.zip

See this forum post that describes how to use a few new properties for debugging and configuring SSLConfig/CipherSuites and SSLConfig/Protocols:

SSL configuration improvements in 3.1.106 or greater

Charlie