This mechanism cannot be used to add new ciphers. Undefined ciphers will be ignored.

This API is only available in Mono and Xamarin products.

You can filter and/or re-order the ciphers suites that the SSL/TLS server will accept from a client. The first match for a supported client cipher suite will be used (so the order is important).

The following example removes weak (export) ciphers from the list that will be offered to the server.

ServicePointManager.ClientCipherSuitesCallback += (SecurityProtocolType p, IEnumerable<string> allCiphers) => {
    return from cipher in allCiphers where !cipher.Contains ("EXPORT")
    select cipher;
};
	  

Example: Use AES128 (preference) or AES256 (allowed) but no other ciphers.

ServicePointManager.ClientCipherSuitesCallback += (SecurityProtocolType p, IEnumerable<string> allCiphers) => {
    string prefix = p == SecurityProtocolType.Tls ? "TLS_" : "SSL_";
    return new List<string> { prefix + "RSA_WITH_AES_128_CBC_SHA", prefix + "RSA_WITH_AES_256_CBC_SHA" };
};