Analyzing security of small-state cipher ATOM for bitstream and image encryption
Yash Makwana, Anupama Panigrahi, Saibal Kumar Pal · Journal of Cyber Security Technology · 2025
Lightweight cryptography is crucial for resource-constrained devices, including RFID Tags, Smart Cards, and medical devices. It becomes essential to analyze lightweight cryptosystems available in the literature before deploying them for various purposes. Motivated by this, we perform a security analysis of the recently proposed small-state lightweight stream cipher, ATOM, against algebraic and cubic attacks. We find that, despite the cipher’s small state size, the effective complexity increases due to the reintroduction of the key in the keystream generation process. We analyze the cipher under reduced rounds, and the use of a single key filter, instead of the two filters specified in the ATOM structure. We report non-randomness in the count function, which depends on the internal state of the keystream generator, and analyze this non-randomness using histograms and linear complexity profiles. We also apply a cubic attack to the modified ATOM and obtain linear equations after summing over selected cubes. Our analysis affirms the use of two key filters and the security of the cipher for lightweight applications. Moreover, we analyze its security in the context of image encryption using techniques such as NPCR, UACI, and SSIM.