A new technique of generating Diffie-Hellman type 2D shared secret key for two or more than two users is proposed. The sizes of private keys P, Q and the base matrix G are easily scalable to large values. Then the consequent common secret key size will also be large so that the chances of key theft and discovery by unauthorized outsiders are very low. Since the secret key is 2D matrix, it can be used for encryption/decryption of document images and other block oriented data.