I have my own private key string, i.e.
-----BEGIN RSA PRIVATE KEY----- MIICXAIBAAKBgQCSAYYgzvGTww.... .... .... ..... 3yUMYj9oYzqdrRHP0XgD0cEEvyqPBwLaNsRdFw
I found some purely Javascript based solution, if it is useful to anyone. You can find the JS Libraries here.
It has resolved my requirement.