CS283 - Lecture 6 - Part 2 - Additional Topics - Authentication

CS283 - Lecture 6 - Part 2 - Additional Topics - Authentication

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
08/24/10 CS283-172/Fall06/GWU/Vora/Identity All 1 GWU CS 172/283 Autumn 2009 All slides from Bishop’s slide set Lecture 6 Part 2 - Additional Topics - Authentication
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Basics Authentication: the binding of identity to a subject The identity is that of an external entity (e.g. my identity, Matt, etc .) The subject is a computer entity (e.g. a process, etc .) GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 06 – Part 2 - Rev 20091103
Background image of page 2
3 Establishing Identity Establishing Identity can be based on determining one or more of the following What the entity knows ( eg. a password) What the entity has ( eg. a badge, a smart card) What the entity is ( eg. fingerprints, retinal characteristics) Where the entity is ( eg . In front of a particular terminal) GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 06 – Part 2 - Rev 20091103
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 Authentication System An authentication system ( A , C , F , L , S ) consists of A: authentication information that proves identity C: complementary information stored on a computer and used to validate authentication information F: complementation functions ; f : A C L: authentication functions that verify identity l: A × C {true, false} S: selection functions enabling an entity to create or alter information in A or C GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 06 – Part 2 - Rev 20091103
Background image of page 4
5 An Example of an Authentication System A password system, with passwords stored on line in clear text A: the set of strings making up passwords C: = A F: singleton set of identity function { I } L: single equality test function { eq } S: function to set/change a password GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 06 – Part 2 - Rev 20091103
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
6 Passwords Password Characteristics A Sequence of characters Examples: 10 digits, a string of letters, etc . Generated randomly, by a user or by a computer with user input A Sequence of words Examples: pass-phrases Algorithms Examples: challenge-response, one-time passwords GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 06 – Part 2 - Rev 20091103
Background image of page 6
7 Password Storage Store as cleartext If the password file is compromised => all passwords are revealed Encipher the password file The OS still needs to have decipherment and encipherment keys in memory This reduces to the previous problem Store a one-way hash of passwords In this case, if the hash file is read, the attacker must still guess passwords or invert the hash GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 06 – Part 2 - Rev 20091103
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
8 Example UNIX system standard hash function Hashes the password into an 11 character string using one of 4096 hash functions As an authentication system: A = { strings of 8 chars or less } |A| = 127 8 2245 6.9 × 10 16 possible password values C = { 2 char hash id || 11 character hash } |C| = 64 13 2245 3 × 10 23 F = { 4096 versions of modified DES }
Background image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 08/24/2010 for the course CS 211 taught by Professor Staff during the Spring '08 term at George Mason.

Page1 / 41

CS283 - Lecture 6 - Part 2 - Additional Topics - Authentication

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online