I 've generated a key with the keytool of java, and I 've exported the public key in ".cer" file. Next, I used my certificate in the SecurityOptions, and have made a secure socket with SecureTcpClient class. Problem : when I run my client, I received the exception that I need a private key in my certificate. Why do I need a private key in the certificate of the client!!!???

Because the client has to sign a hash with the client certificate during the handshake.

How create this private key ?????? I've also generated a key with keytool. I don't know where I must find the private key.