Now-a-days with the global acceptance of the Internet, the people communication becomes faster and easier. Every computer is connected virtually to every other through internet. Therefore, cryptography becomes a crucial aspect for secure communication to protect important data from eavesdroppers. In this paper, a session based bit level symmetric key cryptographic technique has been proposed. It is based on the concept of Doubly Even Order Magic Square and termed as DEOMS. DEOMS considers the plain text as a stream of finite number of binary bits. This binary bit stream is chopped dynamically into manageable-sized blocks. The values of block length of any particular session generate the session key for DEOMS.