An Implement of DES for Keeping Length Identical and Its Application

Because the standard symmetric cryptographic algorithm DES cannot implement the operations of encryption and decryption for any length over 8 bytes, this paper defines DES-based data cryptographic functions, which can keep the byte length of input and output messages identical. These cryptographic functions have been successfully applied in secure transmission for the APDU of the smart card. An Implementation of these functions and their application in the smart card has been detailed