###### Abstract  
The development of cryptography is closely related to the development of computers. The Data Encryption Standard (DES) of 1975 is not used nowadays as it is susceptible to brute-force attack due to its short key sizes. Public-key cryptography is the core of secure cryptographic communication, as it provides protocols such as key management and digital signatures. The security of public-key cryptography is based on hard mathematical problems. The term 'hard', in this context, means that it is difficult to solve in the current computing environment. Hence, analyzing the security of cryptographic algorithms in the forthcoming computing environment--quantum computing--is important.  
This Special Issue aims to present state-of-the-art technologies in the area of cryptosystems in the post-quantum world. Villanueva-Polanco and Angulo-Madrid present the first cold-boot attacks on SIKE (Supersingular Isogeny Key Encapsulation), which was one of the candidates of the NIST PQC standardization project [1]. Another study on the isogeny-based algorithm is detailed in [2]. In [2], performance and security analysis for the CSIDH-variants are thoroughly discussed. In [3], [PERSON] et al. present an optimized implementation of the NIST-P256 curve in an 8-bit processor. As ECC will still be used before transitioning to a quantum computing environment, this study will have a positive influence on related fields. In [4], [PERSON] and [PERSON] present an efficient parallel implementation of the CTR mod of ARX-Based block ciphers on microcontrollers. Since symmetric key cryptography is less affected by the quantum computing environment than public-key cryptography, the optimization of block ciphers has become more important in the field of encryption. The proposed work can be readily applied to 5G mobile telecommunications and IoT devices. In [5], [PERSON] et al. present an efficient implementation of PRESENT and GIFT in quantum computers. They also compare this implementation with other results of lightweight block cipher implementation in quantum circuits and analyze the quantum security of PRESENT and GIFT. In [6], [PERSON] et al. measure the avalanche properties of RC4 stream cipher variants to analyze reported weaknesses regarding the existence of statistical dependencies between the inputs and the outputs, based on the use of strict avalanche criterion and the bit independence criterion.  
Additionally, research related to biometric authentication and homomorphic encryption, which are emerging authentication and encryption methods, is also presented. In [7], a reusable improved fuzzy vector signature method is proposed for biometric information. In [8], [PERSON] et al. propose two methods of HE-based model selection to determine the complexity of models that can explain encrypted data well.  
The NIST's announcement of the standardization project of post-quantum cryptography, a great deal of research has been conducted regarding the quantum computing environment in general, as well as public-key cryptography. Although submissions for this Special Issue have been closed, more in-depth security analysis and implementations of post-quantum cryptography in a quantum computing environment, and the development and implementation of quantum cryptography, are expected.  
**Author Contributions:** Conceptualization, S.H.; Writtings, S.K.; Validation, S.H. and S.K. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2022R1F1A1063611).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data are contained within the article.  
**Conflicts of Interest:** The authors declare no conflict of inteereest.