International Journal of Computer and Internet Security. ISSN 0974-2247 Volume 2, Number 1 (2010), pp. 67--76 © International Research Publication House http://www.irphouse.com Visual Cryptography for Authentication Using CAPTCHA A. Vinodhini 1 and L. Jani Anbarasi 2 1 Lecturer, GKM College of Engineering, Tambaram, Chennai E-mail:vino.aug@gmail.com 2 Assistant Professor, Jerusalem College of Engineering, Pallikkaranai, Chennai- 600100 E-mail:janiherbert79@gmail.com Abstract Authenticity of the user is the major issue in today’s internet applications such as core banking. Password has been the most used authentication mechanism which is subjected to offline and online dictionary attacks. Today hacking of the databases on the internet, is unavoidable. It is difficult to trust the information on the internet. To solve this problem this paper proposes a CAPTCHA based Visual Cryptography scheme to address the authentication issues. This methodology generates a unique CAPTCHA image for users which in turn is divided into two shares. One share is stored in the bank database and the other share is provided to the customer. Hash code is generated for the customer share and it is stored in the bank database. The customer has to present the share during all of his/her transactions. When the customer presents his share the hash code is generated and compared with the database value.. If it matches the shares are stacked to get the original CAPTCHA image which authenticates the user. Introduction Trusting information on the internet is quite difficult due to hacking of database on the internet. So it is nearly impossible to be sure whether a computer that is connected to the internet can be trustworthy and secure or not. In a core banking system there is a possibility of encountering forged signature for transaction. In the net banking system, the password of the customer can be hacked and misused. This paper proposes a technique to improve security and to prevent hacking of database. An idea based on image processing and Visual Cryptography is used. Visual Cryptography introduced by Naor and Shamir[1] is a method used for encrypting a secret image into