Tech Summary

Confidentiality Service

$$ Alice \rightarrow E_k(m) \rightarrow Bob $$

Authentication and Data Integrity

In PGP and S/MIME, $$ Alice \rightarrow m||Alice’s\ digital\ signiture\ on\ m \rightarrow Bob $$ In most real-world security systems, $$ Alice \rightarrow m||h_k(m) \rightarrow Bob $$

Providing Mutual Authentication

Type-1: Kerberos-like protocol, $$ Alice \rightarrow E_k(ID_A||ID_B||timestamp) \rightarrow Bob \ Alice \leftarrow E_k(ID_B||ID_A||timestamp) \leftarrow Bob $$ where $k$ is a pre-shared secret key.

Type-2: challenge-response protocol, $$ Alice \rightarrow E_{K_e^B}(N_1) \rightarrow Bob \ Alice \leftarrow N_1 \leftarrow Bob $$ This is to allow Alice to authenticate Bob. Authentication in the other direction is similar.

Establishing a Common Secret Key

Type-1: digital-envelop method, $$ Alice \rightarrow E_{k_e^B}(k) \rightarrow Bob $$ Type-2: Diffie-Hellman protocol,

where $p$ and $\alpha$ are publicly known.

Reference

Lecture slides of HKUST CSIT5710, by Prof. Cunsheng DING