Dissatisfied with Kerberos (he's difficult to please), Prof. Pedantic proposes a simpler protocol called Chomp ChompTM...

   

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Dissatisfied with Kerberos (he's difficult to please), Prof. Pedantic proposes a simpler protocol called Chomp ChompTM that eliminates the use of the TGS. Let IDc and IPC be the respective ID and IP address of the client, IDy be the ID of the service that the client wishes to access, Kc be a pre-shared key between the KDC and client, Ky be a pre-shared key between the KDC and service V, Kc,y be a temporary key generated by the KDC during the course of the protocol, Ex (M) be the encryption of M using key X, and lifetime be the lifetime of a ticket. Finally, let A → B : M denote the transmission of message M from A to B. Prof. Pedantic's protocol works as follows: (i) Client → KDC: IDC, IDv (ii) KDC → client: Ekc (Kcv, lifetime, tickety), where tickety = Eky (Kc,v, IDc, IPC, lifetime). (iii) Client → service V: tickety, EKcy (IDC, IPC, t), where t is the current time. (iv) Service V→ client: Excy (t+1). (a) {5 points} Does ChompChompTM achieve client authentication? How (if yes) or why not (if no)? (b) {5 points} Does Chomp ChompTM achieve server authentication? How (if yes) or why not (if no)? (c) {5 points} What key goal of Kerberos does Chomp ChompTM not achieve? Why not? Dissatisfied with Kerberos (he's difficult to please), Prof. Pedantic proposes a simpler protocol called Chomp ChompTM that eliminates the use of the TGS. Let IDc and IPC be the respective ID and IP address of the client, IDy be the ID of the service that the client wishes to access, Kc be a pre-shared key between the KDC and client, Ky be a pre-shared key between the KDC and service V, Kc,y be a temporary key generated by the KDC during the course of the protocol, Ex (M) be the encryption of M using key X, and lifetime be the lifetime of a ticket. Finally, let A → B : M denote the transmission of message M from A to B. Prof. Pedantic's protocol works as follows: (i) Client → KDC: IDC, IDv (ii) KDC → client: Ekc (Kcv, lifetime, tickety), where tickety = Eky (Kc,v, IDc, IPC, lifetime). (iii) Client → service V: tickety, EKcy (IDC, IPC, t), where t is the current time. (iv) Service V→ client: Excy (t+1). (a) {5 points} Does ChompChompTM achieve client authentication? How (if yes) or why not (if no)? (b) {5 points} Does Chomp ChompTM achieve server authentication? How (if yes) or why not (if no)? (c) {5 points} What key goal of Kerberos does Chomp ChompTM not achieve? Why not?

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