## 2 Literature
This article consisted of RFID authentication protocols' analysis and comparison by using tree-based authentication, randomized access control, and third-party authentication protocol. A 5G network authentication key exchange (AKE) protocol for multi-server architecture was demonstrated by [PERSON] et al. [29]. The AKE in this paper overcame the perfect forward secrecy and privilege insider attack using several timestamps and the validation of the session keys. A roaming service, which was a mobile network used for mutual authentication of mobile users for privacy preservation, was presented by [PERSON] et al. [30]. Securing roaming mobile networks against the impersonation of valid mobile devices with clock synchronization was performed by multiplicative group, modulo, and prime number calculations for public key authentication. Blockchains used for the transfer of parcels between UAVs were presented by [PERSON] et al. [31]. The UAVs exchange the parcels based on their barcode/RFID/tag identification, which is then authenticated after updating the distributed ledger in the blockchain server based on a smart contract. Authenticating secure device Industrial IoT by using a blockchain was demonstrated by [PERSON] et al. [32]. The devices in the Industrial IoT (IIoT) were secured by using identity-based signatures and ephemeral elliptic curve Diffie-Hellman (ECDHE) key exchange techniques, utilized for the authenticating and key agreement operations. Authentication in distributed systems by incorporating a blockchain was presented by [PERSON] et al. [33]. A two-factor authentication workflow was designed by receiving a one-time password entry and distributed ledger entry by using an ECDH public key within the blockchain. A hybrid blockchain authentication of identity for multiple WSNs was demonstrated by [PERSON] et al. [34]. Local and public blockchains were used for hybrid authentication of the WSN nodes. Blockchain-based distributed data validation and authentication were presented by [PERSON] et al. [35]. A data-chunk-associated digital signature was added to every part, which was generated by a private key and could be verified by multiple entities using a public key within the blockchain distributed ledger. Blockchain-based authentication using telecom networks for two-factor transactions was presented by [PERSON] et al. [36]. Instead of depending on a one-time password, a third-party merchant helps directly authenticate via blockchain for payment transactions. The customer credentials are utilized for one-time password generation secured by the private key. Secured identity management using a blockchain was presented by [PERSON] et al. [37]. The digital identity of the user was stored on a permissioned blockchain that could be verified by a passport or driving license, and later for identity authentication, and a blockchain entry for ledger records to keep track of the identity. The following are the limitation/s that were observed in the above-given literature survey:  
* High amount of calculation on resource-constrained devices: As most of the protocols above use high-end mathematical models, for zero-knowledge proofs, they are found to be inefficient for IoT resource-constrained devices;
* Not suitable for authenticating a large number of devices: As the protocols have a high amount of calculation, as well as were not tested with IoT device experiments, they are not assured to have better performance in fog/edge computing;
* No details provided for protocol verification: A protocol is verified and found safe from various attacks when presented with protocol verification (logic of authentication [38]), which was found to be missing in most of the papers.