The key schedule algorithm (KSA) is a crucial element of symmetric block ciphers with a direct security impact. Despite its undeniable significance, the KSA is still a less focused area in the design of an encryption algorithm. PRESENT is a symmetric lightweight block cipher that provides the optimal balance between security, performance, and minimal cost in IoT. However, the linear functions in KSA lead to a slow and predictable bit transition, indicating the relationship between round keys. A robust KSA should produce random and independent round keys irrespective of the secret key. Therefore, this research aims to improve the KSA PRESENT-128 block cipher with enhanced randomness, round key bit difference, and the avalanche effect. The experiments on round keys and ciphertext with random, low density and high-density secret key datasets endorse the expected improvements. Moreover, the results show that the improved KSA produces random round keys that successfully pass the NIST randomness test. The bit transition from one round key to another is increased from 20% to 40%, where a greater inclination of the avalanche effect has an increased effect with 50% bit change. On the other hand, the improved KSA PRESENT requires an additional $0.001871$ s to generate round keys, as a security cost trade-off.

The vast interconnection of resource-constrained devices and the immense amount of data exchange in the Internet of Things (IoT) environment resulted in the resurgence of various security threats. This resource-constrained environment of IoT makes data security a very challenging task. Recent trends in integrating lightweight cryptographic algorithms have significantly improved data security in the IoT without affecting performance. The PRESENT block cipher, a standard and lightweight benchmark algorithm, is a widely accepted and implemented algorithm with a simple design, low-cost implementation, and optimum performance. However, this simple design utilizing lightweight linear and non-linear functions led to slow confusion and diffusion properties. The static bits in the permutation layer are the leading cause of slow diffusion, showcasing dependencies between plaintext and ciphertext bits. This research addresses and seeks to overcome this shortcoming of slow confusion and diffusion using the Deoxyribonucleic Acid (DNA) replication process and shift-aided operations, leading to the DNA-PRESENT block cipher. Security, cost, and performance analyses were performed to verify the improvements. The results demonstrated that with only 33.5% additional cost, DNA-PRESENT increased key sensitivity to 73.57%, plaintext sensitivity to 33%, and consistently ensured an average bit error rate (BER) of 50.2%. An evident increase of 176.47 kb/s in throughput and reduced latency to 17 cycles/block kept the good hardware efficiency of 43.41 kbps/KGE, and the reduction in execution time by 0.2333 s led to better performance. Considering the security advances achieved, this cost increase is a trade-off between security and performance.