The present work deals with a new symmetric key cryptographic method using dynamic key. The demand for adequate security to electronic data system grows high over the decades. In the present work the authors have used the Linear Congruential Generator (LCG) for generating key. This is a block cipher technique. The advantage of the present method is that for every pair of encryption & decryption operation a new dynamic key is generated thus the process is very hard to break. The cryptography no longer relies on long term shared keys which are vulnerable under cryptanalysis attacks. It is impossible to detect patterns with which to perform cryptanalysis on the dynamic key. In the present work the authors have introduced concept of dynamic key with symmetric cryptography. Dynamic key is similar to one time pad. In this paper, a dynamic key theory is described and mathematically analyzed. In the present method author proposed a cryptography system in which four rounds of encryption & decryption are performed. In each round different parts of dynamic key are applied in order to make it hard against cryptanalysis attacks.

Symmetric key cryptography Encryption Decryption Dynamic key Linear Congruential Generator