# Quantum Authentication Evolution: Novel Approaches for Securing Quantum Key Distribution
## 5 QKD Authentication Model Setup and Details
### Mono-Authentication  
Our initial exploration delves into determining the optimal steps within the protocols for authentication. In the sole authenticated QKD experimental implementation currently available [23], the implemented signature scheme involves signing and verifying at multiple stages of the protocol [57]. This investigation aims to discern the most effective points within the protocol for the authentication process. Mono-authentication, as defined in this context, refers to a process where authentication unfolds at various stages throughout the communication. In Figure 1, we pinpoint precisely where these signature operations take place. This approach involves incorporating authentication mechanisms at multiple steps to enhance the overall security and integrity of the communication process. We advocate for a mono-authentication style, wherein the signature generation occurs after the key exchange, concluding the communication. This approach involves [PERSON] signing all the information she has transmitted to [PERSON], sending it to [PERSON] for verification, and vice versa. Figure 1: The signature style within the BB84 protocol is characterized by several key components [57]. In terms of communication, a visual representation is provided through the use of continuous orange arrows denoting information sent via the classical channel. Conversely, dotted orange arrows signify communication through the quantum channel, emphasizing the exchange of quantum information. The PQC algorithm is used to sign the [PERSON] and [PERSON] message digest and the nonce under their respective private keys to generate signatures. [PERSON] communicates his readiness to [PERSON] by transmitting the basis in which he has measured each bit, denoted as \(\Psi^{B}_{bB}\). Subsequently, [PERSON] initiates the crucial process of basis sifting. This involves [PERSON] identifying and retaining bits in her bit string, \(\Psi^{A}_{dAB}\), that align with [PERSON]'s chosen basis, while discarding those with a mismatched basis. Following this initial sifting, [PERSON] generates a new random bit string, \(\Psi^{A}_{indAB}\). This string plays a pivotal role in determining which bits [PERSON] will make public, forming \(\Psi^{A}_{dkhAB}\), and which bits she will preserve a secret key, denoted as \(\Psi^{A}_{KAB}\). Specifically, \(\Psi^{A}_{chkAB}\) encompasses the substring of \(\Psi^{A}_{dAB}\) for which the corresponding bits in \(\Psi^{A}_{indAB}\) are set to 1, while \(\Psi^{A}_{KAB}\) is composed of bits where the indicator is 0. Upon completing this intricate process, [PERSON] publicly discloses \(\Psi^{A}_{bAB}\), \(\Psi^{A}_{indAB}\), and \(\Psi^{A}_{chkAB}\). Importantly, [PERSON]'s revelation of her basis choice at this stage holds significance, as [PERSON] has already measured the transmitted qubits. This proactive measure ensures that quantum communication remains secure, guarding against potential interference from eavesdroppers. [PERSON] engages in a thorough comparison between [PERSON]'s encoded bit string, \(\Psi^{A}_{bAB}\), and his own measured counterpart, \(\Psi^{B}_{bAB}\). During this process, he discards bits in his measured bit string, \(\Psi^{B}_{dAB}\), where the basis choices deviate from [PERSON]'s selections. Subsequently, leveraging the previously generated random bit string \(\Psi^{A}_{indAB}\), [PERSON] follows a procedure akin to [PERSON]'s to obtain his sifted bit string components: \(\Psi^{A}_{chkAB}\) (the revealed bit string) and \(\Psi^{B}_{KAB}\) (the final secret key). It is noteworthy that the alignment of \(\Psi^{B}_{chkAB}\) with \(\Psi^{A}_{chkAB}\) is pivotal, as it allows [PERSON] to determine the number of matching bits between the two. This comparison becomes the basis for estimating the QBER in the derived key.