Sayed Javad Mousavi - Department of Information Technology, Faculty of Industrial Engineering Tarbiat Modares University Tehran, Iran
Kamal Chaharsooghi - Department of Information Technology, Faculty of Industrial Engineering Tarbiat Modares University Tehran, Iran
Gholam Ali Montazer - Department of Information Technology, Faculty of Industrial Engineering Tarbiat Modares University Tehran, Iran

First and most important step to making secure end-to-end encryption is key exchange. X۳DH is one of the most used protocols to do that. It uses a trusted server to exchange keys. If the key exchange is secure then we have identification, authentication, integrity, non-repudiation, and confidentiality for messages. In X۳DH, if the trusted server is compromised the entire end-to-end encrypted connection will be exposed. Transport Layer Security (TLS) is used for client-server communication. Therefore, the whole security is based on a certificate authority (CA) therefore there will be the single point of failure. In this paper, we proposed using blockchain as a trusted medium to exchange keys and identity authentication. The proposed method is based on the use of X۳DH in instant messaging. This method improves the first step of the X۳DH algorithm which includes authentication. This is the first time using blockchain directly to identify a user.

End-to-end encryption, X۳DH, Asymmetric encryption, Blockchain, Identity key, Authentication