International Journal of Computer Applications
Now-a-days internet is one of the most important sources of communication and thousands of people interact electronically. For sending sensitive messages over the internet, the authors need security. Hence for secure communication required the algorithms. Among these algorithms is Twofish, a promising 128-bit block cipher and one of the competitors in National Institute of Standards and Technology's (NIST) AES competition, for the replacement of DES at the core of many encryption systems world-wide. In this paper the security algorithm, twofish has been explained with all of its modules (some modules has been modified) for both 128 and 192-bit key size. Implementation on VHDL using Xilinx - 6.1 xst software has been done taking delay as main constraint.