Advanced Operating Systems: Lecture 40 - Mr. Farhan Zaidi

Advanced Operating Systems - Lecture 40: Authentication. This lecture will cover the following: user authentication; password based authentication; UNIX password scheme; one-time password schemes; challenge response authentication; biometrics and other authentication schemes; access control and authorization;...

CS703 ­ Advanced  Operating Systems

By Mr Farhan Zaidi

40

 User authentication

 Challenge response authentication

 Biometrics and other authentication schemes

 Access control and authorization

 Access control matrix

 Usually done with passwords

 This is usually a relatively weak form of authentication, since it’s something that people have to remember

 Empirically is typically based on wife’s/husband’s or kid’s name, favorite movie name etc

 Passwords should not be stored in a directly-readable form

 Use some sort of one-way-transformation (a “secure

hash”) and store that

 if you look in /etc/passwords will see a bunch of gibberish associated with each name That is the password

 Problem: to prevent guessing (“dictionary attacks”) passwords should be long and obscure

 unfortunately easily forgotten and usually written down

 Unix password security

Encrypt passwords

 One time passwords

Lamport’s clever scheme (Read Tanenbaum for details)

 Challenge-Response based authentication

Used in PPP and many other applications

 Badge or key

Does not have to be kept secret usually some sort of picture

ID worn on jacket (e.g., at military bases)

 Should not be forgeable or copy-able

 Can be stolen, but the owner should know if it is

 (but what to do? If you issue another, how to invalidate old?)

 This is similar to the notion of a “capability” that we’ll see later

 Biometrics

 Authentication of a person based on a physiological or behavioral characteristic

 Example features:

 Face, Fingerprints, Hand geometry, Handwriting,

 Iris, Retinal, Vein, Voice.

 Strong authentication but still need a “Trusted Path”.

 Context

 User has entered a name and password, or other info

 OS must be designed so monitor cannot be bypassed

User  process

Decide whether user can apply operation to resource

Reference monitor

File 1 File 2 File 3 … File n User 1 read write - - read

User 2 write write write -

…

Subjects

Objects

 Access control list (ACL)

 Store column of matrix

with the resource

 Capability

 User holds a “ticket” for

each resource

File 1 File 2 …

…

Access control lists are widely used, often with groups

Some aspects of capability concept are used in Kerberos, …