User Authentication By Eric Sita

Message Security Privacy: To expect confidentiality from a sender. Authentication: To be sure of someone's identity. Integrity: Make sure message arrives as sent. Nonrepudiation: To prove a message came from a particular sender.

Methods Covered Use of a symmetric Key Using a nonce Bi-directional SSH example

Symmetric Key

Using a nonce

Bi-directional

Example System SSH – Used for our UNIX accounts Consists of three protocols: 1) SSH-TRANS -Transport Layer Protocol 2) SSH-AUTH - Authentication Protocol 3) SSH-CONN - Connection Protocol

SSH-TRANS Provide an encrypted channel between client and server Runs on top of a TCP connection This is first step in logging on to system Uses RSA to authenticate Establish a session key

SSH-AUTH Three methods: 1) Since connection is secure send password 2) Public key encryption 3) Host-based authentication

Extra Info on SSH OpenSSH a package on most UNIX systems supports the command, “SSH- keygen” to create private/public key pairs Is used on other TCP applications like X Windows and IMAP mailers, otherwise known as “SSH tunnel” This is called Port Forwarding, used in the SSH-CONN protocol

SSH Example

References Forouzan, Behrouz Data Communications and Networking McGraw-Hill 2004 Peterson, Larry Computer Networks A Systems Approach Morgan Kaufman 2003 Leon-Garcia, Alberto Communication Networks McGraw-Hill 2000