# Quantum Authentication Evolution: Novel Approaches for Securing Quantum Key Distribution
## 4 Strengthening QKD: Advancing Security through Post-Quantum Cryptography  
In the post-processing phase of quantum communication, conducted within the conventional channel accessible to the public, users must prioritize verifying the authenticity of their communication partners and ensuring the integrity of public messages to prevent unauthorized alterations. To address this security vulnerability, we recommend incorporating authentication measures to establish a stronger and more secure framework, thereby protecting against potential threats to the integrity of quantum communication. Authenticating the classical channel in QKD protocols entails various methods. However, some rely on pre-distributed keys from the initial round, which poses scalability challenges [55; 56]. An optimal solution involves utilizing a Public Key Infrastructure (PKI). In this approach, trust is centralized in a Certificate Authority (CA), eliminating the need for individual user trust. The CA manages the distribution of public and private keys for each user, facilitating effective authentication through signature and verification algorithms. This PKI-based approach enhances scalability and trust within the QKD protocol. Digital signatures are crucial for verifying the authenticity of transmitted data. This scheme comprises three key components: the key-pair, consisting of public and secret keys generated through a key generation algorithm; the signing algorithm, which creates the signature; and the verifying algorithm, which determines the success or failure of the verification process given the public key and message. These signatures guarantee the integrity and origin of exchanged data, thereby affirming the authenticity of the key exchange. Signatures play a pivotal role in ensuring information-theoretic security within QKD. As long as the authentication process remains uncompromised during communication, QKD security is maintained at an information-theoretic level. This security remains resilient against decryption attempts, even if the public key signature is deciphered later [57]. Thus, reliance on the public key signature emerges as a singular and crucial element in the overallsecurity framework. It is essential to emphasize that when referring to signatures, we encompass the entire verification process. The effectiveness of digital signatures depends on the complexity of a mathematical challenge. This challenge, when combined with the right public and private keys, is easily solvable, but its difficulty escalates without the correct keys. In our efforts, we utilize exclusively post-quantum algorithms, which are based on mathematical problems resistant to decryption attempts by quantum computers. These algorithms are chosen for their ability to withstand cryptanalytic attacks enabled by quantum computing capabilities. We now introduce mathematical challenges that pose significant hurdles even for quantum computers, along with the algorithms designated for inclusion in this study. All these algorithms are finalists in the National Institute of Standards and Technology (NIST) competition, strategically designed to standardize optimal algorithms in response to the looming threat posed by quantum computers. The selection process involves rigorous evaluation through multiple rounds of analysis. It is important to note that while these algorithms currently demonstrate resilience against decryption attempts, they face the challenge of potential vulnerabilities emerging from future cryptanalysis. Recently, one algorithm encountered a security breach, prompting a reevaluation of its robustness, highlighting the dynamic nature of cryptographic landscapes and the continuous effort to stay ahead of emerging threats. Our initial focus is on lattice-based cryptosystems, renowned for their well-rounded performance. Notable algorithms grounded in this mathematical problem include CRYSTALS-DILITHIUM [58] and FALCON [59], which have officially been announced by NIST to standardize them.