cit 380: securing computer systems - faculty.cs.nku.edu

CIT 380: Securing Computer Systems Slide #1

CIT 380: Securing Computer Systems

Authentication


Topics

1. Identity 2. Groups and Roles 3. Network Identities 4. Authentication 5. Biometrics 6. UNIX Authentication

Slide #2


What is Identity? Computer’s representation of an entity

– Entities can be subjects or objects. Authentication binds a principal to an identity. Example:

– username expresses your identity. – password binds the person typing to that

particular identity (username).

Slide #3


Purpose of Identity

Access Control – Most systems base access rights on identity of

principal executing the process.

Accountability – Logging and auditing functions. – Need to track identity across account/role

changes (e.g., su, sudo).

Slide #4


Groups and Roles An “entity” may be a set of entities referred to by

a single identifier. Principals often need to share access to files, and

thus are taken as groups. – static: alias for a group of principles. – dynamic: principal changes from one group to another

as different privileges are needed.

role: a group that ties membership to function

Slide #5


Network Identity Ethernet (MAC) Address

– 48-bit data link level identifier – example: 00:0B:DB:78:39:8A

IP Address – 32-bit network level identifier – ex: 10.17.0.101

IPv6 Address – 128-bit network level identifier – ex: fe80::2a0:c9ff:fe97:153d/64

Hostname (DNS name) – string application level identifier – ex: www.nku.edu

Slide #6


What is Authentication?

Binding of an identity to a subject Based on:

1. What the entity knows (e.g., passwords) 2. What the entity has (e.g., access card) 3. What the entity is (e.g., fingerprints) 4. Where the entity is (e.g., local terminal)

Multi-factor authentication

Slide #7


What You Know

• Passwords • Pass Phrases • PINs

Slide #8

Presenter

Presentation Notes

http://www.infosecblog.org/2007/09/why-good-passwords/


What You Have

• Smart Cards • USB Token • RFID

RFID used for toll collection

Slide #9


USB Tokens and Smart Cards

Small device with storage and processor. – USB tokens tend to focus on storage. – Smart cards on processor + small storage. – Differences are growing smaller.

Methods of use – By Hand (read card and type one-time

password) – USB – Wireless

Slide #10


RFID Radio Frequency Identification Types of Tags

– Passive: use power from reader signal – Active: internal power source

Applications – Product tracking (EPC barcode replacement) – Transportation payment – Automotive (embedded in car keys) – Passports – Human implants

EPC RFID Tag

Slide #11


What You Are: Biometrics

Identification by human characteristics: 1. Physiological 2. Behavioral

A biometric characteristic should be: 1. universal: everyone should have it 2. unique: no two people should share it 3. permanent: it should not change with time 4. quantifiable: it must be practically measurable

Slide #12


How Biometrics Work 1. User submits sample. 2. Software turns

sample into digital template.

3. Software compares template against stored reference template.

4. Authentication based on how closely templates match.

Slide #13


Biometric Measurement

Possible Outcomes:

1. Correct person accepted 2. Imposter rejected 3. Correct person rejected (False Rejection) 4. Imposter accepted (False Acceptance)

Slide #14


False Positives and Negatives

Tradeoff between False Accept Rate False Reject Rate

Slide #15


Fingerprints Capacitive measurement, using differences in

electrical charges of whorls on finger to detect those parts touching chip and those raised.

Slide #16

Presenter

Presentation Notes

Attacks: Forcing authorized user to grant access. Recover latent fingerprint impression. Artificial gummy fingers made from molding plastic/gelatin 68-100% successful when tested against 11 types of fingerprint auth systems.


Brandon Mayfield

• Fingerprints found in 2004 Madrid bombing. • Brandon arrested May 6, 2004. • FBI claimed “100 percent positive” match.

– Held under a false name. – Then transferred to unidentified location.

• Spanish police identify fingerprint as belonging to an Algerian man May 21, 2004.

• Brandon released May 25, 2004.

Slide #17


Eye Biometrics Iris Scan

– Lowest false accept/reject rates of any biometric.

– Person must hold head still and look into camera.

Retinal Scan – Cataracts and pregnancy

change retina pattern. – Lower false accept/reject

rates than fingerprints. – Intrusive and slow.

Slide #18


Other Types of Biometrics

Physiological

• DNA • Face recognition • Hand geometric • Scent detection • Voice recognition

Behavioral

• Gait recognition • Keyboard dynamics • Mouse dynamics • Signatures

Slide #19

Presenter

Presentation Notes

http://ducknetweb.blogspot.com/2013/09/cardiac-rhythm-bracelet-selling-for-79.html


Biometrics are not infallible

What are False Accept and Reject Rates? Do the characteristics change over time?

– Retina changes during pregnancy. – Fingerprint damage due to work/pipe smoking. – Young and old people have fainter fingerprints.

Is it accurate in the installed environment? – Is someone observing fingerprint or voiceprint

checks? – i.e., did you collect biometric from the person?

Slide #20


Biometrics can be compromised. Unique identifiers, not secrets.

– You can change a password. – You can’t change your iris scan.

Examples: – You leave your fingerprints every place. – It’s easy to take a picture of your face.

Other compromises. – Use faux ATM-style devices to collect biometrics. – Obtain all biometric templates from server.

Slide #21


Use and Misuse of Biometrics Employee identification.

– Employee enters login name. – System uses fingerprint to verify employee is who he

claims to be. – Problem: Does biometric match the employee?

Criminal search (Superbowl 2001) – System uses face recognition to search for criminals in

public places. – Problem: Does any biometric in database match anyone

in a crowd of people? – Assume system is 99.99% accurate and 1 in 10million

people is a terrorist. Result: 1000 false positives for each terrorist.

Slide #22

Presenter

Presentation Notes

"But the case for face recognition is straightforward. They were looking for two of the terrorists and had photographs of them. Face recognition systems in airports would have caught them." I'm not sure we really know that the authorities had photographs that were good enough for face recognition, even for those small number of suspects that they claim to have placed on a terrorist watch list. But even if we grant the premise, not much follows from it. First, the fact that the authorities suspected only two of the nineteen hijackers reminds us that automatic face recognition cannot recognize a face until it is in the database. Most hijackers are not on lists of suspected terrorists, and even if those particular hijackers had been prevented from boarding their planes, seventeen others would have boarded.


Location Classic: only allow access from a particular

terminal or a particular set of remote hosts.

Modern: GPS-based – Location Signature Sensor (LSS) for host and user. – Access rules permit user only to access host with

specific LSS values. – Cell-phones track location, and some states use

them to track drivers’ speed and locations.

Presenter

Presentation Notes

http://en.wikipedia.org/wiki/Gps


UNIX Authentication

UNIX identifies user with a UID – Username is for humans, UID for computers. – 15-bit to 32-bit unsigned integer. – UID=0 is the superuser, root.

Identity and authentication data stored in – /etc/passwd

– /etc/shadow

– /etc/group

Presenter

Presentation Notes

http://www.3connected.com/techfaq.php


/etc/{passwd,shadow}

/etc/passwd – Username – UID – Default GID – GCOS – Home directory – Login shell

/etc/shadow – Username – Encrypted password – Date of last pw change. – Days ‘til change allowed. – Days `til change required. – Expiration warning time. – Expiration date.

Central file(s) describing UNIX user accounts.

student:x:1000:1000:Example User,,555-1212,:/home/student:/bin/bash student:$1$w/UuKtLF$otSSvXtSN/xJzUOGFElNz0:13226:0:99999:7:::

Slide #25


Groups and GIDs

GIDs are 32-bit non-negative integers. Each user has a default GID.

– File group ownership set to default GID. – Temporarily change default GID: newgrp.

Groups are described in /etc/group – Users may belong to multiple groups. – Format: group name, pw, GID, user list. – wheel:x:10:root,waldenj,bergs

Slide #26


Superuser Powers

Superuser can • Read any file. • Modify any file. • Add / remove users. • Become any user. • Kill any process. • Reprioritize processes. • Configure network. • Set date/time. • Shutdown / reboot.

Superuser can’t • Change read-only

filesystem. • Decrypt hashed

passwords. • Modify NFS-mounted

filesystems. • Read or modify SELinux

protected files.

Slide #27


Switching Users The su command allows you to switch users.

> id uid=102(wj) gid=102(wj) groups=102(wj) > su Password: # id uid=0(root) gid=0(root)

groups=0(root),1(bin),2(daemon),3(sys),4(adm), 6(disk),10(wheel)

# su john john$ id uid=1995(john) gid=1995(john) groups=1995(john) john$ exit # exit > id uid=102(wj) gid=102(wj) groups=102(wj)

Slide #28


Real and Effective UIDs

Real UID – The UID matching the username you logged in as.

Effective UID – The UID that is checked for access control. – The su command changes your EUID.

SUID programs – A SUID program executes with an EUID of the

owner of the program instead of yours. – /usr/bin/passwd is SUID root. Why?

Slide #29


Key Points 1. Access control is based on identity. 2. Authentication consists of an entity, the user,

attempting to convince another entity, the verifier, of the user’s identity

1. something you know 2. something you have 3. something you are 4. somewhere you are

3. Authentication Types 1. Passwords 2. Security Tokens 3. Biometrics

Slide #30


References 1. Phil Agre. “Your Face is not a Bar Code,” http://polaris.gseis.ucla.edu/pagre/bar-

code.html, 2003. 2. Ross Anderson, Security Engineering, 2nd edition, Wiley, 2008. 3. Matt Bishop, Introduction to Computer Security, Addison-Wesley, 2005. 4. DigitalPersona, http://www.digitalpersona.com/company/news/pressKit.php, 2006. 5. Simson Garfinkel, Gene Spafford, and Alan Schwartz, Practical UNIX and Internet

Security, 3/e O’Reilly, 2003. 6. Ben Mook, “Md. pilot program tracks drivers’ speed, location via cell phones,” The Daily

Record, October 21, 2005, http://www.mddailyrecord.com/pub/5_398_friday/businessnews/172883-1.html

7. Bruce Schneier, “Biometrics: Truths and Fictions,” Cryptogram, http://www.schneier.com/crypto-gram-9808.html#biometrics, 1998.

8. Bruce Schneier, “The Curse of the Secret Question,” http://www.schneier.com/essay-081.html, 2005.

9. Orville Wilson, “Privacy & Identity - Security and Usability: The viability of Passwords & Biometrics,” http://facweb.cs.depaul.edu/research/vc/CIPLIT2004/ppt/Orville_Wilson.ppt, 2004.

10. “Simple Anatomy of the Retina,” http://webvision.med.utah.edu/sretina.html, 2006.

Slide #31

http://polaris.gseis.ucla.edu/pagre/bar-code.html

http://polaris.gseis.ucla.edu/pagre/bar-code.html

http://www.digitalpersona.com/company/news/pressKit.php

http://www.schneier.com/crypto-gram-9808.html

http://www.schneier.com/essay-081.html

http://www.schneier.com/essay-081.html

http://facweb.cs.depaul.edu/research/vc/CIPLIT2004/ppt/Orville_Wilson.ppt

http://webvision.med.utah.edu/sretina.html

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