# Experimental Quantum Message Authentication with Single Qubit Unitary Operation
## 1 Introduction  
Modern cryptography provides four functions, namely, confidentiality, authentication, integrity, and nonrepudiation [1, 2]. Therefore, as a substitution candidate for next-level secure cryptography, quantum cryptography should also have the ability to offer these four functions. Remarkable progress has been made in the area of confidentiality because the quantum key distribution (QKD) protocol that provides confidentiality has been considerably improved [3, 4, 5, 6]. QKD aims to enable communication partners, e.g., [PERSON] and [PERSON], to share secret keys and ultimately perform a one-time pad communication. Those protocols provide unconditional confidentiality based on the principle that an arbitrary unknown quantum state cannot be copied and that quantum measurement is irreversible [7, 8, 9, 10]. On the other hand, many researchers have also studied how to use these secret keys in quantum message authentication [11, 12, 13], arbitrated quantum signature [14, 15, 16, 17, 18, 19], or quantum digital signature [20, 21, 22, 23, 24, 25, 26, 27, 28, 29], providing authentication, integrity, and non-repudiation.  
In this paper, we introduce a simple and practical quantum message authentication protocol with a quantum three-pass protocol [30, 31, 32, 33] and a quantum encryption scheme [19, 34]. This protocol is a lightweight to simplify the implementation by removing an arbitrator from our proposed quantum signature protocol [19]. Here, the quantum three-pass protocol is the quantum version of [PERSON]'s three-pass protocol [1, 35], and quantum encryption scheme is to prevent existential forgery, called Gao's forgery. More specifically, the core elements of the proposed protocol, such as the quantum three-pass protocol and the quantum encryption scheme, are implemented with only single qubit unitary operators. In other words, these can be implemented easily by using linear combinations of wave plates [36, 37]. Additionally, the swap test that checks the correspondence of the original message and quantum message authentication code (QMAC) can be implemented using a Hong-Ou-Mandel interferometer [38, 39, 40]. In advance, as the Hong-Ou-Mandelinterferometer is a destructive swap test [40], more resources are needed to implement a controlled swap test.  
In Section 2, we briefly explain the concept of the proposed scheme. Section 3 presents a security analysis of the proposed protocol for [PERSON]'s private key, the forgery of QMAC pair, and the origin authentication of quantum message. Section 4 describes the experimental setup and measurement results. We conducted three experiments with the proposed protocol. First, we implemented a quantum three pass protocol, which is a method of conveying information in the proposed quantum message authentication. Second, we implemented a quantum encryption scheme with a single qubit unitary operator to prevent forgery. Finally, we confirmed that the QMAC pair with the quantum encryption scheme is robust to [PERSON]'s forgery. In Section 5, after a thorough discussion that includes the possibility of expanding the scheme to quantum signature and quantum entity authentication, we present the conclusions of this work.