A company running a social networking website would like to develop a private discussion system to allow a group of users to participate in an online discussion on some sensitive issues. To encourage an open discussion, it is important to enable these users or group members to freely express their opinions without revealing their real identities. This means that an anonymous discussion system is needed to protect the privacy of the users.

To develop the above system, the company has defined a set of requirements, including those listed below which are particularly relevant to this coursework:

(a) A particular user can register as a group leader who is responsible for selecting a discussion topic and managing the group membership.

(b) For the discussion credibility and transparency, every user, who wishes to participate in the discussion, must register with the group leader in order to become a member of the group, where the group leader must authenticate the user based on their real identity. Each group member is allowed to know the real identities of all the other registered users within the group.

(c) Each group member can send messages to all the other group members anonymously. This is done by anonymously creating a sessional/temporary user account with a unique pseudo username and a password for each registered group member in such a way that no single party (a group member, a system or the group leader) can link the real identity of any other group member to their pseudonym. Every group member can then communicate with the others in the group under their pseudo name.

Note that due to licence and cost issues, the company has ruled out the direct use of any existing systems/applications (e.g., Kerberos, PGP, IPSec and SSL/TLS) and decided to go for the development of an in-house solution for the above discussion system.

the question is . Analyse the security of your proposed protocol in detail to show how the protocol achieves the following security properties: Authenticity described in requirement (b) in the Introduction section, including the authenticity of each protocol message, and Anonymity stated in requirement (c) in the Introduction section.