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COEN 350: Network Security Authentication. Between human and machine Between machine and machine.

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Presentation on theme: "COEN 350: Network Security Authentication. Between human and machine Between machine and machine."— Presentation transcript:

1 COEN 350: Network Security Authentication

2 Between human and machine Between machine and machine

3 Human Machine Authentication Authentication protocols are based on What you know. E.g. password, pass-phrase, (secret key, private key). What you have. Physical key, smart card. What you are. Biometrics. Where you are. E.g. trusted machine, access to room, …

4 Authentication Passwords Predate computers. As do some attacks (stealing, guessing) Older cell phone technology transmits originating number with a password. Password good, call goes through. Eavesdropper receives phone number – password combination. Eavesdropper can now clone the phone.

5 Authentication Password Attacks Guessing On-line Time consuming. Authentication attempts are usually logged. Can detect attack long before it is likely to succeed. Can disrupt the attack. Off-line Attacker needs to steal relevant data from which password(s) can be determined. Attacker can use arbitrary amount of computing power. Capturing Passwords Eavesdropping Login Trojan Horse

6 Authentication Passwords are stored On each server Alice uses. Centrally: Authentication Storage Node: Each server retrieves the information when it wants to authenticate Alice. Centrally: Authentication Facilitator Node: Each server takes Alice’s data and password and goes to the AFN.

7 Authentication Password can be stored Unencrypted Simple Dangerous Implicitly as hashes of passwords As in UNIX, VMS Encrypted Hashed and Encrypted

8 Authentication Example: Network Information Service (Yellow Pages) Directory service is the authentication storage node. Stores hashed passwords of users. Typically, hashed passwords list is world readable Access by claiming to be a server. NIS authentication storage node does not authenticate itself to users. Allows impersonation of authentication service.

9 Authentication Passwords for machine – machine communication can be made difficult to guess. Arbitrary length Truly random choice of characters. Human-machine passwords Guessable Subject to dictionary attack.

10 Authentication Dictionary attack Most passwords are natural language words. Or derived from natural language words. Guess the language. Use a dictionary to try out all words in the language. Start with common passwords first. Replace a single character in a word, attach a random character, etc.

11 Authentication Brute-Force Attack Generate all possible password. Sometimes make assumptions on the alphabet only printable character characters on a key-board

12 Authentication Salting Protects hashed passwords against an offline attack. Brute Force attack attacks all passwords in password file simultaneously.

13 Authentication Salting Store a salt with each password Hash depends on salt and password. Use different salts for different passwords. Store salt with password.

14 Authentication Salting Brute force attack, dictionary attack can only attack a single password.

15 Authentication Rainbow tables Simple idea: precompute hashes for all possible passwords, do a look-up in your precomputed table To be useful: Lookup table needs to be simple Use a “reduce” function that maps hashes to passwords Create a chain: Starts with password pwd. Next element is hash ( reduce ( hash (pwd)) Next one is hash ( reduce ( hash ( reduce ( hash (pwd))))) … Do this a few thousand times and only store pwd and last element in chain

16 Authentication Rainbow tables To be useful: Lookup table needs to be simple (continued) Assume now a hash of an unknown password hash ( pwd ) Check whether it is a terminal hash If not, calculate hash ( reduce ( hash ( pwd )) Check whether it is a terminal hash Repeat until you find a terminal hash with password orgpwd. You know that pwd  {orgpwd, hash(reduce(hash(orgpwd)), … }

17 Authentication Passwords are compromised: By obtaining password file. Safeguard by Hashing and Salting Encryption By eavesdropping on an exchange Use one-way passwords: Lamport Hash

18 Authentication Address Based Common in early UNIX Rtools:.rhosts In user home directory (Computer, Account) pairs These pairs are allowed access to the user’s account /etc/hosts.equiv List of network addresses of “equivalent” machines Account name on A is equivalent to account name on B. Users have to have identical account names.

19 Authentication Addressed based authentication threatened by Access escalation Attacker gains access to one hosts. Access cascades to equivalent hosts / rhosts. Spoofing addresses Very easy to spoof source address. Harder to intercept traffic back.

20 Authentication Ethernet network address impersonation Easy on the same link. Hubs do not protect. Switches can be spoofed through the ARP protocol. Routers are harder to fool, but can be attacked and provided with misleading routing data.

21 Authentication Cryptographic authentication Alice proves her identity to Bob by proving to Bob that she knows a secret. Hashes Secret key cryptography Public key cryptography.

22 Human Machine Authentication Initial password distribution to humans Pre-expired, strong passwords Through mail Derivable from common knowledge Student ID

23 Human Machine Authentication Authentication Token Possession of the token proves right to access. Magnetic stripe as on credit cards. Harder to reproduce “Impossible” to guess Demand special hardware Can be lost or stolen Add pin or password protection Are not safe against communication eavesdropping and forging

24 Human Machine Authentication Authentication Token Smart Card. Needs to be inserted in a smart card reader. Card authenticates to the smart card reader. PIN protected smart cards. Stops working after a number of false PINs. Cryptographic challenge / response cards Card contains a cryptographic key. Authenticating computer issues a challenge. Card solves the challenge after PIN is entered. Harder to crack than PIN protected smart cards because key is never revealed.

25 Human Machine Authentication Authentication Token Smart Card. Readerless smart card (Cryptographic calculator) Communicates with owner through mini-keyboard and display. Authenticating computer issues a challenge to Alice. Alice types in challenge into readerless smart card. Readerless smart card solves the challenge. After Alice puts in her password. Alice transfers the answer to the computer.

26 Human Machine Authentication Biometrics Retinal scanner Fingerprint reader Face recognition Iris scanner Handprint readers Voiceprints Keystroke timing Signatures

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