# Authentication and Billing for Dynamic Wireless EV Charging in an Internet of Electric Vehicles
## 3 Related Works  
### EV Authentication in DWC Systems  
Different authentication techniques are proposed in the literature for DWC systems. A fast authentication for a dynamic EV charging (FADEC) model is proposed in [41], to provide fast message signatures, fast signature verification, and low communication overhead. The proposed system utilizes DSRC for the information exchange between the EVs and the road side units (RSUs). The cryptographic techniques employed for authentication include hash-based message authentication code (HMAC), Elliptic Curve Digital Signature Algorithm (ECDSA), and Just Fast Keying (JFK), which is a key exchange protocol based on the Diffie-Hellman protocol. The scheme is designed such that the same key is used to authenticate each EV to multiple RSUs, based on EV driving route estimation from traffic statistics, to avoid re-authentication and reduce handover latency. Nevertheless, this scheme does not preserve the privacy of the EV as the charging pad owners can determine the exact location of the EVs and can use this data for vehicle tracking.  
To address the issue of EV location privacy, an anonymous authentication scheme is proposed by the authors in [42] using verifiable encryption, authenticated pairwise-keys and coin hash chains. The EV identity is preserved by using pseudonyms instead of its real identity, and a hash chain is used for verification purposes. A similar approach is also adopted in [9] and fast authentication is achieved using symmetric keys involving the spatiotemporal location of the EV. The scheme proposed in [9] further enhances the privacy of EV information and ensures lightweight authentication by eliminating the need for communication between the charging segments, allowing the EV to exchange the corresponding encrypted messages securely with each segment as it approaches it.  
The authors in [43] also propose an efficient authentication protocol for dynamic charging using blind signatures and hashing. The process is initiated when the charging company generates keys and the EV purchases these keys and un-blinds them, while they are being verified by the charging management controller. The EV then uses a hash chain to authenticate itself to the charging segments and starts charging. Hence, the charging pads do not need to share any keys with the pad owner, and the EV anonymously authenticates itself to the pad owner using the blind signatures. Another authentication approach is proposed in [44; 45], using partial blind signatures, hashing, and one-time tokens to formulate a secure and privacy-preserving physical-layer-assisted authentication model. However, while hash key verification is computational efficient for authentication between the EVs and the charging segments, the verification of blind signatures requires exponential operations and bilinear pairing, which increases the overall computational cost of the authentication models presented in [43; 44; 45].  
A lightweight authentication and charging management scheme for DWC systems is also proposed in [46], involving EV registration and power negotiation with the charging controller, referred to as power supply station (PSS), and hierarchical token-based authentication with the RSUs. The DWC system in [46] assumes the charging energy is harvested from renewable energy sources (RES) and hence, power negotiation is essential to guarantee energy availability. The proposed system utilizes pseudonyms and digital signatures to first register the EVs with the PSS, then uses asymmetric key cryptography for power negotiation and demand management. The mutual authentication between the EVs and different system entities, using signature verification and public/private key pairs, ensures reliability and security of the message exchange process.