How to setup Oracle SSL using self-signed certificate between client and DB?
I found the answer.

In my post I've described how to create trusted and user certificates. As I guess trusted certificate is public key and user certificate is a private key(correct me if I am wrong).

Now I write how I have done this job.

--on DB server

Run owm(Oracle Wallet Manager) and:


Create new wallet. 
Create certification request.
Export certification request.
using ssl.ca-0.1(Downloaded from http://www.openssl.org/contrib/) created self-signed root certificate using new-root-ca.sh and imported as a trusted certificate on DB server.
Created self-signed server certificate by running the sign-server-cert.sh and imported as an user certificate on DB server.


--On client server
Copied root certificate(generated previously).


Create new wallet.
Create certification request.
Import trusted certificate by choosing copied root certificate.


Edit tnsnames.ora file on client server to use TNS entry using protocol TCPS and port, for example, 2484. 

Edit listener.ora file on DB server to listen port 2484 and protocol TCPS.

Open Net Manager and configure SSL on both sides.

--DB side

Indicate wallet directory.

I've unchecked "Require Client Authentication" 
and other options what you want.

--Client side

Indicate wallet directory..

and other options what you want.