CIS 551 / TCOM 401

February 23, 2006

Lecture 12: Digital Signatures


Needham-Schroeder Public Key Authentication

Example of Protocol:

Flaw:

A       -- Km {Na, A} -->               M       -- Kb {Na, A} -->        B
A                                       M       <-- Ka {Na, Nb} --       B
A       <-- Ka {Na, Nb}                 M                                B
A       -- Km {Nb} -->                  M                                B
A                                       M       -- Kb {Nb} -->           B

Digital Signatures

Digital Signatures with Shared Keys

Digital Signatures with Public Keys

Primary Attacks

Multiple Use of Keys