World is rapidly going to be hi-tech. In this IT era, each sector is highly influenced with computer and internet. With the use of computers every work is done with more accuracy, fast and efficient way. Daily companies or industries come with new services and facilities to provide better services to their users. Surely, it has increased facilities but the other face is it has also increased the chances for malicious users or hackers. In order to develop more secure software, it will be beneficial to check or quantify its security at initial level of software development. The design phase is one of the strong phases that hold the complete software. During the phase, the whole software architecture is developed. During the design phase we get a complete idea of how the software will work and changes made at this level is easier than other phases. Security of the software cannot be measured directly. It can be measured with the combined use of models, metrics and attributes. A Security estimation life cycle has been developed to estimate security at design stage. Security estimation process covers complete security quantification of software.