# SIMECK-T: An Ultra-Lightweight Encryption Scheme for Resource-Constrained Devices
### Related Work  
The related work consists mostly of ARX block ciphers specifically designed for software implementations. These are considered a new paradigm in lightweight cryptography [8]. A detailed survey in [35] presents TEA [30] as the third most energy efficient algorithm [10], third in the least number of cycles [36], first in least cycles, least cycles per byte and combined metric [37], first in code size and second in the Random Access Memory (RAM) requirements [37], third in the cycles/block metric [38], third in the code size metric [38] and, most importantly, the first in speed out of 13 software-oriented ciphers [39]. A good balance of speed, lightness and security is obtained using encryption primitives designed for a 64-bit block size and a key size of 96 or 128 bits. A more recent survey on lightweight cryptography [40] lists HIGHT [41], SPECK [7], LEA [42], SPARX [43] and CHAM [44] as new software-oriented lightweight block ciphers, where SPECK is considered the fastest, having 0 RAM requirements and only 186 bytes read-only memory (ROM) requirements. SPECK was designed for software implementations, and SIMON [7] was designed to be more efficient in hardware. SPECK-R is a SPECK variant with only seven rounds where RC4 [20] substitution boxes are used in order to maintain similar security levels to the full round version of the cipher [19]. Although IoT devices have limited memory and may be slow to access it, another approach to lightweight cipher design that has a 4 by 4 substitution box is proposed by [PERSON] et al. [45]. TErrestrial Trunked RAdio (TETRA) encryption ciphers like TEA2 and TEA3 developed by the European Telecommunications Standards Institute (ETSI) were made available to the public [46] due to surveillance and backdoor suspicions [32]. These ciphers have been used by important agencies in Europe, but also abroad. Critical infrastructure protection depends on them, but they were available until recently only under a non-disclosure agreement (NDA). The ciphers themselves have been long known to be dependable and are considered to this day unbreakable from a cryptography point of view. However, the implementation vulnerabilities of some versions once again prove that closed-source software is not to be trusted. HIGHT [41] uses 8-bit instructions, and attacks have been published for all rounds [47; 48]. Although oriented on 32-bit instructions, LEA [42] is a 128-bit block cipher, having 24 rounds for a 128-bit key. This makes it inefficient when less than 16 bytes need to be encrypted, as is frequently the case with IoT. CHAM [44] is very slow using 80 rounds. The revised versions use a minimum of 88 rounds, and the authors claim that the speed in the software is comparable to that of SPECK [49]. But SPECK has 26 rounds for a 128-bit key, and our benchmarks show that SPECK is faster. SPARX [43] is an ARX cipher with provable limits, designed for 16-bit instructions. It is based on SPECK. The key schedule takes a 128 bit master key and turns it into 96-bit subkeys. Because it is designed for 16-bit microcontrollers, it is not efficient on 32-bit devices. At the same time that the survey was made available [35], the SIMECK cipher was published [29]. SIMECK combined the best of SPECK and SIMON from the National Security Agency (NSA) [7] into a single, fast lightweight cipher, using only ARX instructions, relying on the AND operator for non-linearity. SIMECK was designed with high performance parallelization in mind [50]. TEA [30] is notorious for its tinyness, having simplicity and memorability as design goals. TEA has been used in parallel implementations for RFID [51] applications or single instruction multiple data (SIMD) environments like graphic processing units (GPUs) [52]. XTEA [53] is a corrected form of TEA, with a larger number of rounds. It is also notably slower. XXTEA [54] is the corrected version of XTEA (also called block TEA or BTEA), which is also slower than TEA. CHACHA [55] is a 256-bit block cipher that aims to have better diffusion per round compared to SALSA [55].