# A Systematic Survey on 5G and 6G Security Considerations, Challenges, Trends, and Research Areas
## 5 Proposed Future Security Mechanisms
### Post-Quantum Cryptography
#### 5.2.1 Possible Post-Quantum Ciphers  
As post-quantum ciphers do not have the traditional building blocks of a normal cipher, they do not have a direct 1:1 relationship [123]. The authors in [123] offer four post-quantum ciphers that would protect against confidentiality attacks when quantum devices are more relevant and powerful. These four algorithms are: Lattice-Based Cryptography,Hash-Based Cryptography, Code-Based Cryptography, and Supersingular Elliptic Curve Isogeny Cryptography. The Lattice-Based approach incorporates an NP-hard problem into cryptography. This method takes a normal vector lattice and seeks to find the shortest non-zero vector in the vector space spanned by the basis vectors. NTRU [124] is a commonly known Lattice-Based scheme, which has been tested and revised into two new standards; IEEE Standard 1363.1 and ANSI standard X9.98. Hash-Based Cryptography incorporates the eXtended Merkle Signature Scheme (XMSS), as blockchain technology has been studied more robustly. One code-based approach is the [PERSON] scheme, which was introduced in 1978. [PERSON] based his method on the implementation of computing random linear transformations of an error-correcting code's generator matrix. Only the private key holder would know the factors of the matrix. Oftentimes, this method is overlooked for PQC due to it needing extremely long keys [125].  
NIST has made great strides over the recent decade in verifying and vetting quantum-resistant cryptographic algorithms from research groups around the world. NIST made a public call for submissions in December of 2016 and has narrowed the field of algorithms down to three as of the publication of this paper. Three drafts were published as part of the Federal Information Processing Standards (FIPS) in August of 2023, showcasing post-quantum algorithms resistant to quantum computer decryption methods. Each draft includes a complete description of each algorithm and its constituent functions. FIPS 203 [126], based on CRYSTALS (Cryptographic Suite for Algebraic Lattices)-Kyber [127], is also referred to as the Module-Lattice-based Key-Encapsulation Mechanism Standard that allows users to generate a shared secret key for communication over a public channel. FIPS 204 [128] is based on the CRYSTALS-Dilithium approach [129] and is also known as the Module Lattice-Based Digital Signature Standard. Originally published in the CRYSTALS-Dilithium paper, the authors share that their implementation operates in constant time and has a public key 2.5 times smaller than the previously most efficient lattice-based schemes. In FIPS 205 [130], the Stateless Hash-Based Digital Signature Standard, based on the SPHINCS+ [131] paper submission, is used to protect messages and to perform the verification and validation of digital signatures. As 5G progresses in its rollout and maturation in the near future, it is imperative that post-quantum cryptography is incorporated in areas where current classical algorithms are at risk in order to maintain the confidentiality and integrity of user data. This also applies to other standards on the internet, such as TLS. The best-case scenario for such standards would support PQC drop-in replacements. In order to make this a reality, associated Certification Authority (CA) infrastructure is necessary to issue, manage, and revoke these new PQC keys, however [123].