SECURING LEGACY INDUSTRIAL SYSTEMS: A SYSTEMATIC REVIEW OF DES ENHANCEMENTS AND RNS APPLICATIONS IN CRYPTOGRAPHY (2020–2025)

Abstract

Legacy industrial systems including Supervisory Control and Data Acquisition (SCADA) and other Industrial 
Control Systems (ICS) continue to depend on the Data Encryption Standard (DES), despite its age and documented 
weaknesses. Although DES offers speed and simplicity, especially in hardware-constrained environments, its 56-bit 
key and predictable structure leave it highly vulnerable to brute-force attacks. In recent years, researchers have 
worked on improving the security concern of the DES algorithm, such as key whitening, block expansion and 
mathematical computation of the DES process. An emerging area involves the use of the Residue Number System 
(RNS). RNS is a modular arithmetic that is known for parallelism operations and fault tolerance advantage. RNS has 
been applied in the field of cryptography to speed up computations and for data obfuscation, which makes it suitable 
for lightweight encryption process. However, most researchers concentrated on the application of RNS in public-key 
cryptographic algorithms and hardware acceleration, while its application in symmetric encryption especially DES 
remains rare. This review was guided by PRISMA 2020 standards which considered researches published between 
the year 2020 and year 2025, focusing on recent enhancement made on DES algorithm, the use of RNS in 
cryptography, and emerging approaches or methods for securing legacy systems. The gap in integrating RNS with 
DES was spotted as a novel idea for improving the security concern of outdated but still widely used ICS while 
avoiding computational complexity.