Efficient and secure selective cipher scheme for MIoT compressed images

Recently, the pervasiveness of multimedia contents raised serious security and privacy concerns, especially with limited devices such as the ones used in the Multimedia Internet of Things (MIoT), which are constrained in terms of computations, memory capacity and power consumption. In this paper, we propose a lightweight format-compliant compression–selection cipher scheme, which could be adopted with different types of image compression algorithms (lossless or lossy). The two proposed cipher variants leverage the compressed data characteristics such as randomness and uniformity, as compared to uncompressed data; this distinguishes the proposed solution from the existing ones. Also, the proposed cipher supports configurable encryption parameters, such as the encryption data rate, to satisfy the requirements of the different MIoT applications, and to optimize the trade-off between security and efficiency. The two proposed variants, which do not require additional operations to produce a format-compliant code-stream, are based on the dynamic key approach, and they require a single round of simple operations. The first variant consists only of one cryptographic operation, permutation or substitution, while the second variant consists of two operations, permutation and substitution. The low number of rounds, combined with simple operations, result into low computational complexity and consequently, low energy consumption and latency. The process for updating the permutation and substitution tables is also lightweight, and it could be implemented in parallel for each sub-compressed part (tile or frequency level), which increases the security level at a minimal computational cost. The proposed substitution, permutation, and substitution–permutations variants exhibit a high throughput with an enhancement of at least 311%, 176%, and 125% compared to the optimized Advanced Encryption Standard (AES) implementation, respectively.