**5. Conclusions**

A novel hyper-chaotic system based image encryption scheme is proposed with 3D transformed Zigzag and RNA operation in this paper. By using the 6D hyper-chaotic system, three auxiliary matrices are generated, including one permutation index matrix, one mask matrix for Zigzag, and one codon table index matrix. Subsequently, two rounds 3D transformed Zigzag diffusion mechanism is proposed for pixels diffusion with each other. Nevertheless, additional encryption with RNA codons makes more reliable and secure results through employing codons tables and security keys. Through simulations, the proposed HCZRNA has better performances on the resistance of different types attacks than the compared encryption schemes, while the speed is not ideal, since it is a complex process. On the premise of ensuring performance, we would simplify diffusion and RNA operation processes and optimize the encryption steps for improving speed in the future.

**Author Contributions:** Conceptualization, D.Z. and T.L.; Data curation, L.C.; Formal analysis, D.Z.; Funding acquisition, T.L.; Investigation, T.L.; Methodology, D.Z. and T.L.; Project administration, T.L.; Resources, D.Z.; Software, D.Z.; Supervision, D.Z. and T.L.; Validation, L.C. and T.L.; Visualization, L.C.; Writing—original draft, D.Z.; Writing—review & editing, T.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Ministry of Education of Humanities and Social Science Project (Grant No. 19YJAZH047) and the Scientific Research Fund of Sichuan Provincial Education Department (Grant No. 17ZB0433).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data available on request.

**Acknowledgments:** We gratefully acknowledge the reviewers for their comments and suggestions.

**Conflicts of Interest:** The authors declare no conflict of interest.
