authentication what you know? what you have? what you are?

Authentication

What you know?

What you have?

What you are?

Authentication CSCE 522 - Farkas/Eastman -- Fall 2005 2

Authentication Allows an entity (a user or a system) to

prove its identity to another entity Typically, the entity whose identity is

verified reveals knowledge of some secret S to the verifier

Strong authentication: the entity reveals knowledge of S to the verifier without revealing S to the verifier


Authentication Information

Must be securely maintained by the

system.


Elements of AuthenticationPerson/group/code/systemDistinguishing characteristicProprietor/system

owner/administratorAuthentication mechanismAccess control mechanism


Authentication RequirementsSystem must ensure

Data exchange is established with addressed peer entity and not with an entity that masquerades or replays previous messages

Data source is the one claimed


Authentication vs. IdentificationIdentification – Who are you?Authentication – Why should we

believe you?Authentication generally follows

identification


User AuthenticationWhat the user knows

Password, personal informationWhat the user possesses

Physical key, ticket, passport, token, smart card

What the user is (biometrics) Fingerprints, voiceprint, signature

dynamics


PasswordsFor each user, system stores (user

name, F(password)), where F is some transformation (e.g., one-way hash) in a password file

When user enters the password, system computes F(password); match provides proof of identity


F(password)Password F(password): easy F(password) password: hardPassword is not stored in the

system


Vulnerabilities of PasswordsEasy to guess or snoopNo control on sharingVisible if unencrypted in networksSusceptible for replay attacks if

encrypted naively


Advantages of PasswordsEasy to modify compromised

passwordSystem well understood by most

usersSpecialized hardware not needed


Weak PasswordsBell Labs study (Morris and

Thompson, 1979), 3289 passwords were examined

Summary: 2831 passwords (86% of the sample) were weak, i.e., either too easy to predict or too short


Study Details 15 single ASCII characters 72 two ASCII characters 464 three ASCII characters 477 four ASCII characters 706 five letters (all lower case or all upper case) 605 six letters, all lower case 492 weak passwords (name, dictionary words,

etc.)


Password AttacksGuessing attackDictionary attackSocial engineeringSpoofing attackOther attacks (covered later)


Guessing AttackExploits human tendency to use

easy to remember passwordsTrial-and-error attackEasy to detect and block (failed

logins)Need audit mechanism


Dictionary Attack Attack 1:

Create dictionary of common words and names and their simple transformations

Use these to guess password Attack 2:

Usually F is public and so is the password file (encrypted)

Compute F(word) for each word in dictionary Find match


Social EngineeringAttacker asks for password by

masquerading as somebody else (not necessarily an authenticated user)

May be difficult to detectProtection against social engineering:

strict security policy and user education


Login SpoofingCreate a fake login screenCapture login and password when user

attempts to log inPresent a fake failed login screenUser may not even notice there is a

problem


Password DefensesPassword saltPassword management policiesLamport’s schemeOne time passwordsTime synchronizationChallenge response


Password Salt Used to make dictionary attack more difficult Salt is a 12 bit number between 0 and 4095 Derived from system clock and the process ID Compute F(password+salt); both salt and

F(password+salt) are stored in the password table User: gives password, system finds salt and

computes F(password+salt) and checks for match Note: with salt, the same password is computed in

4096 ways


Password Management Policies Educate users to make better choices Define rules for good password selection

and ask users to follow them Ask or force users to change their password

periodically Actively attempt to break user’s passwords

and force users to change broken ones Screen password choices


Lamport’s scheme Doesn’t require any special hardware System computes F(x),F2(x),…, F100(x) (this

allows 100 logins before password change) System stores user’s name and F100(x) User supplies F99(x) the first time If the login is correct, system replaces F100(x) with

F99(x) Next login: user supplies F98(x) … and so on User calculates Fn(x) using a hand-held calculator,

a workstation, or other devices


One-time Password Use the password exactly once! Often done for initial assigned

passwords User must change password before

doing anything else


Time Synchronized There is a hand-held authenticator

It contains an internal clock, a secret key, and a display Display outputs a function of the current time and the

key It changes about once per minute

User supplies the user id and the display value Host uses the secret key, the function and its clock

to calculate the expected output Login is valid if the values match


Challenge/Response

Work station Host

Network

Non-repeating challenges from the host The device requires a keypad

User ID

Challenge

Response


Challenge/Response Problems

Key database is extremely sensitiveThis can be avoided if public key

algorithms are used


Devices with Personal Identification Number (PIN)Devices are subject to theft Some devices require PIN (something

the user knows)PIN is used by the device to

authenticate the user


Smart CardsPortable devices with a CPU, I/O ports,

and some nonvolatile memoryCan carry out computation required by

public key algorithms and transmit directly to the host

Some use biometrics data about the user instead of the PIN


BiometricsFingerprintRetina scanVoice patternSignatureTyping styleHand geometry


Problems with BiometricsExpensive

Retina scan (min. cost) about $ 2,200 Voice (min. cost) about $ 1,500 Signature (min. cost) about $ 1,000

False readings Retina scan 1/10,000,000+ Signature 1/50 Fingerprint 1/500

Can’t be modified when compromised


Errors in BiometricsFalse rejection rate (FRR)

Authorized subject is rejectedFalse acceptance rate (FAR)

Unauthorized subject is acceptedCrossover error rate (CER)

FRR = FAR


Two-factor AuthenticationRequire two forms of

authenticationPassword + smart cardPIN + hand geometry


Wellness CenterIdentification – SSNAuthorization – hand geometryHigh change of random hands

matchingLow chance of your friend’s

hand matching yours


Single Sign-On (SSO)Provide identification and

authorization once for a set of related systems

VIP limited SSOKerberos (ker-ber-OUS)

Symmetric key cryptosystem Trusted third party (Key Distribution Center

(KDC) – a trusted third party


Responsibility for DataData owner (data administrator)

Sets policies

Data custodian (database administrator) Implements policies

Data user (database user) Follows policies


Chapter Topic ReviewAccess controlIdentification and

authenticationPossible threatsMiscellaneous examples

authentication what you know? what you have? what you are?

Documents

user authenticationwhat

password filewhen user

user knowspassword

system stores user

easy fpassword password

verifierstrong authentication

authentication informationmust

user possessesphysical