# Quantum Authentication Evolution: Novel Approaches for Securing Quantum Key Distribution
## 4 Strengthening QKD: Advancing Security through Post-Quantum Cryptography
The prominence of lattice-based cryptosystems lies in their believed effectiveness across various cryptographic metrics, positioning them as robust contenders in the evolving landscape of post-quantum cryptographic solutions. Another mathematical problem under consideration is multivariate-based cryptography, which relies on solving systems of multivariate polynomial equations. RAINBOW was initially a candidate rooted in this problem domain [60]. However, it is crucial to note, RAINBOW has been eliminated from consideration. In cryptographic terms, a primitive is considered \"broken\" when an attack compromises its security level, failing to uphold its advertised robustness. This elimination underscores the rigorous evaluation process and the commitment to ensuring cryptographic solutions maintain their advertised levels of security. In conclusion, we shift our focus to hash-based cryptosystems, which offer one-time signature schemes based on hash functions and the security assumptions of one-way functions. An exemplary solution in this domain is SPHINCS+ [61], which has officially been announced by NIST. Hash-based cryptosystems, leveraging the robustness of one-time signature schemes, contribute to the evolving landscape of post-quantum cryptographic solutions, providing an alternative approach to address security challenges posed by quantum advancements. A critical consideration is ensuring the resilience of authentication algorithms to prevent unauthorized access for at least the number of bits exchanged. The concept of the security level, indicating the efficacy of signature algorithms, encapsulates this necessity. For an exchanged key of \(n\) bits, the security level mandates that an attacker would need to perform \(2^{n}\) operations to successfully guess the key. The post-quantum signature algorithms utilized in this study, CRYSTALS-DILITHIUM, SPHINCS+, and RAINBOW, are selected to offer distinct security levels. We explore security levels equivalent to 128, 192, and 256 bits of security. Notably, CRYSTALS-DILITHIUM and RAINBOW offer algorithms catering to all these security levels. Each algorithm's name, contingent on the security level, is detailed in Table 1. This meticulous consideration of security levels underscores the commitment to fortifying the authentication process against potential breaches. Having established the foundational concepts, we now turn our attention to the methodology and contributions of this work based on QKD authentication model integrated with PQC. Our forthcoming analysis focuses on a comparative evaluation of the performance exhibited by the four post-quantum algorithms introduced earlier. To provide additional insights, Table 2 presents variations in sizes among various parameters generated by these algorithms. This comparative assessment aims to uncover nuances in their performance characteristics, contributing to a deeper understanding of their applicability and effectiveness in quantum-resistant authentication. Table 2 presents the sizes of signatures and key pairs for each post-quantum algorithm under examination. This table offers a comprehensive overview of key characteristics inherent to the studied algorithms. Notably, it highlights differences, particularly in the signature size for RAINBOW compared to other algorithms. Similarly, distinctions are observed in the key pair size for SPHINCS+. These nuances provide insights into the unique attributes and performance variations among the selected PQC algorithms.