Hybridize Dynamic Symmetric Key Cryptography using LCG

Abstract

In the present work, a block cipher is presented which deals with a dynamic symmetric key cryptographic method using substitution and transposition technique. In this work a dynamic secret key is generated using Linear Congruential Generator (LCG). The striking feature of the present work is creation of a new secret key for every pair of encryption and decryption operation, thus secret key is a dynamic key. After encryption and decryption operation the dynamic key is discarded. The proposed cryptography method is a process consisting of two rounds of encryption and two rounds of decryption. The key generation algorithm uses SHA-1 hashing scheme to produce key of size 196 bits. This key is used to encrypt plain text of variable size. Since this is a block cipher method authors divide the variable size plaintext into ‘n’ fixed size (49 bit) blocks. The notion of dynamic key has evolved from the concept of the one time pad. Different parts of dynamic secret key are used in different places in order to make it harder for cryptanalysis or attacks.