# Blockchain-Enabled Secure and Interoperable Authentication Scheme for Metaverse Environments
## 6 Security Analysis
### Informal Security Analysis  
* Impersonation attack: An adversary can create a fake login username, PU, and password, PW. However, it is not possible to get access to tokens, Ti, that are used at the time of user registration. Also, the Meta-ID that is a 256-bit hash used to uniquely identify users is also mapped to login credentials. To change the Meta-ID, consensus has to achieved in the blockchain network. So, it is not possible to manipulate it using an impersonation attack. Therefore, our scheme prevents impersonation attack. * Replay attack: The replay attack allows an adversary to eavesdrop on the messages being exchanged between users and avatars. However, an adversary will not be able to get access to the private keys and MID of the user and avatar. In our proposed model, the replay attack is avoided using an MIF-sync up with relevant Metaverse server platforms (MPs). Blockchain in the MIF maintains the timestamp of the transaction and also the session key that is being used, SKi, to identify each session. Therefore, the combination of the Meta-ID and session key will prevent s replay attack. * Fake-avatar attack: In this type of attack, the virtual world creates a false avatar to imitate an actual avatar. In order to do this, an adversary is required to possess the Meta-ID and avatar ID (Ai). Also, it would need to be able to verify the PKi with the CA and the MIF, which is highly infeasible as PKi is created using tokens. Also, avatars are mapped to the PID of the PU for which an avatar is created. This means that a fake avatar would need to able to get access to the physical ID of the user. It is highly unlikely that a fake avatar can get access to all of these parameters. Therefore, our scheme is fake-avatar-attack proof. * Stolen-device attack: An adversary can steal a head-mounted device, hand-held device or other related device. However, the device ID is stored in a block masked with a hash. Also, it is combined with a Meta-ID that is stored in the blockchain. Therefore, an adversary cannot gain access to the user information, infoi, through a stolen device. * Stolen-password attack: The user and avatar authentication processes in our scheme are not based only on a password. This authentication requires a physical PID and a metaverse-platform-specific username and password. The Meta-ID hash is generated based on all of the associated parameters. Thus, it is difficult to crack the password of the user by adversary. Therefore, our scheme is stolen-password-attack proof. * Server-spoofing attack: An adversary can intercept messages shared among users and avatars and generate a response message as if it is coming from the legit server MPSi. However, a response message cannot be generated without the private keys of users and avatars. Also, the Meta-ID is added to the messages being sent. Thus, our scheme can resist platform-server-spoofing attacks. * Denial-of-service attack: An adversary can send multiple request messages and transmit them to the MIF or CA for verification. This may lead to a network bottleneck. However, as the metaverse platform checks for the timestamp of the request and session key, the attacker cannot create new request messages. Even if the adversary tries to resend past messages, the MPS will treat them as invalid. Therefore, the proposed scheme guarantees robustness against denial-of-service attacks. * Man-in-the-middle attack: An adversary may try to reuse previously shared messages that have been captured by an attacker. However, the timestamp and Meta-ID mechanisms in our scheme will prevent responses to such invalid requests. Thus, our scheme takes care of MITM attacks. * Non-traceable-avatar attack: All of the messages shared among the users and devices are protected by session keys, SKi, and time stamps, ts. Also, there are unique random numbers associated with users or avatars. That is why our proposed scheme provides non-traceability.