KLEIN is a new family of lightweight block cipher that has advantages in both of software and hardware performances.
Since lightweight ciphers must be implemented in a small and inexpensive way, KLEIN faces more severe challenges such as Side-channel Attacks. Precomputation look-up table masking countermeasure is inexpensive and secure against first-order DPA, therefor is more suitable for lightweight ciphers in resource-constrained devices. Based on precomputation look-up table masking method, we propose an ultra-lightweight masked KLEIN: parallel masked KLEIN-64 requires 55% more area than unprotected KLEIN-64. Meanwhile, serial masked KLEIN-64 requires 66% more area and 33% more time than unprotected KLEIN-64. Experimental results show that masked KLEIN is secure against first-order DPA and
CPA attacks.