In a digital multimedia era, the security of multimedia over network transmission becomes a challenging issue. A strategy, combining cryptography with steganography, is investigated to overcome the problems in hand. This paper proposes hiding secret messages, represented as a binary image, by covering a binary random texture synthesized from a 2D Ising Markov random field with an authorized RSA key as the seed. Experiments show that an unauthorized key may never recover the message even it is close to the authorized one.