# Signature Split Method for a PQC-DSA Compliant with V2V Communication Standards
## 1 Introduction  
Advances in quantum computing may invalidate the discrete logarithm and elliptic curve-based public key cryptography schemes used in current protocols [1]. In various protocols, public key-based schemes such as key exchange algorithms for mutual communication and digital signature algorithms (DSAs) for authentication should be replaced with algorithms that can achieve quantum security in the future. As a result, the National Institute of Standards and Technology (NIST) conducted the Post-Quantum Cryptography (PQC) standardization project. and the selected algorithms to be standardized were recently announced [2]. Efforts to achieve quantum security for protocols are moving in two major directions. The first is a designing hybrid mode, which has the advantage of being more compatible with existing protocols and conforming to standards. The purpose of the hybrid mode is to achieve universal quantum security for common commercial devices. Therefore, hybrid awareness of client and server is important [3]. PQC can be used in environments that are hybrid-aware of each other and able to work with PQC but cannot be used inexisting public-key-based crypto-systems if neither is hybrid-awareHowever, because PQC is based on a variety of mathematical challenges, and algorithm-specific parameters are all different, certain PQC algorithms have difficulty meeting protocol requirements, such as packet size and latency. For example, In the TLS 1.3 protocol, there is a report that failed to mount Classic McEliece, a 3-round candidate for PQC [2]. The second way is to be aware of potential problems in the hybrid mode and revise the instantiation method. This means redesigning existing protocols to more efficiently apply PQC. However, this method has the disadvantage in being difficult to apply unless it is enacted as a standard. Broadcast-based V2V communication has the ultimate goal of secure communication in autonomous driving environments. Autonomous vehicles can receive real-time information from other vehicles, know each vehicle's location, and precalculate their travel paths. In V2V communication. basic-safety messages (BSM)s conforming the IEEE 1609.2 standard allow for the protocol to send and receive the current vehicle state, such as vehicle position and speed [4]. Without a cryptographic algorithm between autonomous driving communications, real-time relocation, rerouting, etc. by attackers could lead to security incidents or even death, so BSM achieves authentication and nonrepudiation through DSA [5]. Since the V2V communication protocol also needs to achieve quantum security in the future, it is a necessary to apply PQC-DSA to the V2V protocol. We consider three research direction perspectives based on V2V communication. The first is to suggest a method for applying the PQC algorithm to the V2V protocol in the application layer. For example, research suggests that Crystals-Dilithium is difficult to use in V2V communication due to its large signature size. Not all protocols used for V2V communication can equipped with Crystals-Dilithium. Dedicated short range communication (DSRC) and WAVE protocols have a BSM packet size of fewer than 2000 bytes [6]; therefore, Crystals-Dilithium with a minimum-security level (2) of 2000 bytes or more signature size cannot be installed. Ultimately, we aimed to apply PQC-DSA with Crystals-Dilithium to all V2V protocols. Therefore, before designing the hybrid protocol, we explored an efficient way to mount Crystals-Dilithium onto V2V communication. The second perspective is the need for simulation in the V2V communication protocol. In the V2V protocol, remote cars broadcasts BSM messages at 100 m/s. Therefore, the local car should verify received BSMs from remote cars. In the V2V protocol, the local car generally verifies in real time the BSMs sent by the surrounding remote cars in standby mode. The count of BSMs received may vary depending on the location of the local car. Therefore, simulations are needed to measure latency.