Chacha 20 is a stream cypher that is used as lightweight on many CPUs that do not have dedicated AES instructions. As stated by Google, that is the reason why they use it on many devices, such as mobile devices, for authentication in TLS protocol. This paper proposes an improvement of chaha20 stream cypher algorithm based on tent and Chebyshev functions (IChacha20). The main objectives of the proposed IChacha20 algorithm are increasing security layer, designing a robust structure of the IChacha20 to be enabled to resist various types of attacks, implementing the proposed algorithm for encryption of colour images, and transiting it in a secure manner. The test results proved that the MSE, PSNR, UQI and NCC metrics of IChacha20 are better than those of the original Chacha20. Also, the proposed method has a faster execution time (01:26:4 sec) compared with the original algorithm (02:07:1 sec).
