The most common problem involves while the internet user logging into the website are phishing and key logger attacks. Most of the people even don't know about them. At present most of the websites and online banking system uses the password contains a word, alphanumeric and special characters which are unique for each and every user. It will contain fixed password characters only. So, It can be stolen by adversaries easily. To prevent this researchers proposed graphical scheme, secret question. In our scheme captcha is created from the server and user performing a simple mathematical operation on the captcha digit. It can be entered along with the fixed part of the password. Our proposed system has a simple UI. User can set the logic as much as possible. Our scheme is immune to the phishing, key logger and bot attacks. In furthermore to add security to our scheme we use the modified RSA crypto system [5] that uses n prime numbers for encryption and decryption of the users credential.

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3. Ming Lei, Yang Xiao, Susan V. Vrbsky, Chung-Chih Li, and Li Liu "A Virtual Password Scheme to Protect Passwords"
4. DetchasitPansa, ThawatchaiChomsiri "Web Security Improving by using Dynamic Password Authentication" IPCSIT vol. 11 (2011) © (2011) IACSIT Press, Singapore
5. B. PersisUrbana Ivy, PurshotamMandiwa. Mukesh Kumar "A modified RSA cryptosystem based on 'n' prime numbers"
6. http://en. wikipedia. org/wiki/RSA_(cryptosystem)

Captcha Rsa Algorithm Security Password Authentication.