>OpenSSL is an open source implementation of the SSL and TLS protocols. The core library (written in the C programming language) implements the basic cryptographic functions and provides various utility functions. [wikipedia]
OpenSSL is provided by default in all linux installations toimplement the Secure Socket Layer operations. Using OpenSSL you canestablish your own certifying authority and generate and sign serverside and client side certificates. More information about the OpenSSLproject can be found here : The OpenSSL Project.
Establishing a certifying authority and generating certificates in an UBUNTU linux installation is particularly easy :

1. #apt-cache search libssl | grep SSL
2. #cd && mkdir -p myCA/signedcerts && mkdir myCA/private && cd myCA
3. #echo ’01′ > serial  && touch index.txt
4. Create an initial caconfig.cnf file suitable for the creation of CA certificates (refer link below)
5. #export OPENSSL_CONF=~/myCA/caconfig.cnf
6. #openssl req -x509 -newkey rsa:2048 -out cacert.pem -outform PEM -days 1825
7. #export OPENSSL_CONF=~/myCA/exampleserver.cnf
8. #openssl req -newkey rsa:1024 -keyout tempkey.pem -keyform PEM -out tempreq.pem -outform PEM
9. #openssl rsa < tempkey.pem > server_key.pem
10. #mv tempkey.pem server_key.pem
11. #export OPENSSL_CONF=~/myCA/caconfig.cnf
12. #openssl ca -in tempreq.pem -out server_crt.pem
13. #rm -f tempkey.pem && rm -f tempreq.pem

The above 13 commands create a CA – create a server certificate andalso sign it. For a much detailed and informative tutorial refer : https://help.ubuntu.com/community/OpenSSL

The above process can also be automated using the CA.pl script whichcomes with the library — this post will be helpful for those who wantto know what goes on inside the script.