1. CIT 380: Securing Computer Systems
Authentication
CIT 380: Securing Computer Systems

2. CIT 380: Securing Computer Systems
Authentication
Identity
Groups and Roles
Network Identities
Authentication
Biometrics
UNIX Authentication
CIT 380: Securing Computer Systems

3. CIT 380: Securing Computer Systems
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).
CIT 380: Securing Computer Systems

4. CIT 380: Securing Computer Systems
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).
CIT 380: Securing Computer Systems

5. CIT 380: Securing Computer Systems
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
CIT 380: Securing Computer Systems

6. CIT 380: Securing Computer Systems
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:
IPv6 Address
128-bit network level identifier
ex: fe80::2a0:c9ff:fe97:153d/64
Hostname (DNS name)
string application level identifier
ex:
CIT 380: Securing Computer Systems

7. What is Authentication?
Binding of an identity to a subject
Based on:
What the entity knows (e.g., passwords)
What the entity has (e.g., access card)
What the entity is (e.g., fingerprints)
Where the entity is (e.g., local terminal)
Two-factor authentication
CIT 380: Securing Computer Systems

8. CIT 380: Securing Computer Systems
What You Know
Passwords
Pass Phrases
PINs
CIT 380: Securing Computer Systems

9. CIT 380: Securing Computer Systems
What You Have
Smart Cards
USB Token
RFID
RFID used for toll collection
CIT 380: Securing Computer Systems

10. 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
CIT 380: Securing Computer Systems

11. CIT 380: Securing Computer Systems
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
CIT 380: Securing Computer Systems

12. What You Are: Biometrics
Identification by human characteristics:
Physiological
Behavioral
A biometric characteristic should be:
universal: everyone should have it
unique: no two people should share it
permanent: it should not change with time
quantifiable: it must be practically measurable
CIT 380: Securing Computer Systems

13. CIT 380: Securing Computer Systems
How Biometrics Work
User submits sample.
Software turns sample into digital template.
Software compares template against stored reference template.
Authentication based on how closely templates match.
CIT 380: Securing Computer Systems

14. Biometric Measurement
Possible Outcomes:
Correct person accepted
Imposter rejected
Correct person rejected (False Rejection)
Imposter accepted (False Acceptance)
CIT 380: Securing Computer Systems

15. False Positives and Negatives
Tradeoff between
False Accept Rate
False Reject Rate
CIT 380: Securing Computer Systems

16. CIT 380: Securing Computer Systems
Fingerprints
Capacitive measurement, using differences in electrical charges of whorls on finger to detect those parts touching chip and those raised.
Attacks:
Forcing authorized user to grant access.
Recover latent fingerprint impression.
Artificial gummy fingers made from molding plastic/gelatin % successful when tested against 11 types of fingerprint auth systems.
CIT 380: Securing Computer Systems

17. CIT 380: Securing Computer 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.
CIT 380: Securing Computer Systems

18. CIT 380: Securing Computer Systems
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.
CIT 380: Securing Computer Systems

19. Other Types of Biometrics
Physiological
DNA
Face recognition
Hand geometric
Scent detection
Voice recognition
Behavioral
Gait recognition
Keyboard dynamics
Mouse dynamics
Signatures
CIT 380: Securing Computer Systems

20. 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?
CIT 380: Securing Computer Systems

21. 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.
CIT 380: Securing Computer Systems

22. 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.
"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.
CIT 380: Securing Computer Systems

23. CIT 380: Securing Computer Systems
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.
CIT 380: Securing Computer Systems

24. CIT 380: Securing Computer Systems
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
CIT 380: Securing Computer Systems

25. CIT 380: Securing Computer Systems
/etc/{passwd,shadow}
Central file(s) describing UNIX user accounts.
/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.
student:x:1000:1000:Example User,, ,:/home/student:/bin/bash
student:$1$w/UuKtLF$otSSvXtSN/xJzUOGFElNz0:13226:0:99999:7:::
CIT 380: Securing Computer Systems

26. CIT 380: Securing Computer Systems
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
CIT 380: Securing Computer Systems

27. CIT 380: Securing Computer Systems
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.
CIT 380: Securing Computer Systems

28. CIT 380: Securing Computer Systems
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
CIT 380: Securing Computer Systems

29. 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?
CIT 380: Securing Computer Systems

30. CIT 380: Securing Computer Systems
Key Points
Access control is based on identity.
Authentication consists of an entity, the user, attempting to convince another entity, the verifier, of the user’s identity
something you know
something you have
something you are
Authentication Types
Passwords
Security Tokens
Biometrics
CIT 380: Securing Computer Systems

31. CIT 380: Securing Computer Systems
References
Phil Agre. “Your Face is not a Bar Code,”
Ross Anderson, Security Engineering, Wiley, 2001.
Matt Bishop, Introduction to Computer Security, Addison-Wesley, 2005.
DigitalPersona,
Simson Garfinkel, Gene Spafford, and Alan Schwartz, Practical UNIX and Internet Security, 3/e O’Reilly, 2003.
Ben Mook, “Md. pilot program tracks drivers’ speed, location via cell phones,” The Daily Record, October 21, 2005,
Bruce Schneier, “Biometrics: Truths and Fictions,” Cryptogram,
Bruce Schneier, “The Curse of the Secret Question,”
Ed Skoudis, Counter Hack Reloaded, Prentice Hall, 2006.
Wikipedia,
Wikipedia,
Wikipedia,
Wikipedia,
Wikipedia,
Orville Wilson, “Privacy & Identity - Security and Usability: The viability of Passwords & Biometrics,”
“Simple Anatomy of the Retina,”
CIT 380: Securing Computer Systems