Medical image protection using hyperchaos-based encryption The increasing utilization of telemedicine, especially the teleradiology services, has raised a great deal of concerns in the security of medical images transmitted over open networks. To meet this challenge, a new medical image protection scheme using hyperchaos-based encryption is suggested in this paper. Improvements have been made to both permutation and diffusion methods to address the security problems encountered by many existing chaos-based image ciphers. In the permutation stage, a pixel swapping-based strategy is introduced instead of using the area-preserving chaotic maps, and the swapping operation is determined by the first two state variables of the employed 4-D hyperchaotic system. During the diffusion procedure, the key stream elements, quantified from the other two state variables, are circularly shifted according to the plain-pixels. Consequently, the keystream is related to both the key and the plain-image, which ensures the security against known/ chosen-plaintext attack. Thorough experimental tests are carried out and the results indicate that the proposed scheme provides an effective way for online secure medical image transmission over public networks.