Authentication andIdentity Management

• Ideally– Who you are

• Practically– Something you know (e.g., password)– Something you have (e.g., badge)– Something about you (e.g., fingerprint)

Basis for Authentication

Password Authentication• Alice inputs her password, computer verifies

this against list of passwords• If computer is broken into, hackers can learn

everybody’s passwords– Use one-way functions, store the result for

every valid password– Perform one-way function on input,

compare result against the list

Password Authentication• Hackers can compile a list of frequently used

passwords, apply one-way function to each and store them in a table – dictionary attack

• Host adds random salt to password, applies one-way function to that and stores result and salt value– Randomly generated, unique and long enough

Password Authentication• Someone sniffing on the network can learn the

password• Lamport hash or S-KEY – time-varying password

– To set-up the system, Alice enters random number R– Host calculates

x0=h(R), x1=h(h(R)), x2=h(h(h(R))),..., x100

– Alice keeps this list, host sets her password to x101

– Alice logs on with x100, host verifies h(x100)=x101, resets password to x100

– Next time Alice logs on with x99

Password Authentication• Someone sniffing on the network can learn the

password– Host keeps a file of every user’s public key– Users keep their private keys– When Alice attempts to log on,

host sends her a random number R– Alice encrypts R with her private key

and sends to host– Host can now verify her identity by

decrypting the message and retrieving R

• Key Distribution– Confidentiality not needed for public key– Can be obtained ahead of time

• Performance– Slower than conventional cryptography– Implementations used for key distribution, then use

conventional crypto for data encryption• Trusted third party still needed

– To certify public key– To manage revocation

Public Key Authentication

• Passport• Shibboleth

Single Sign-On

• Goal is single sign-on– Solves problem of weak or repeated user/pass

combinations• Implemented via redirections

– Users authenticate themselves to a common server, which gives them tickets

– Similar flavor to Kerberos but different environment – many organizations

• Widely deployed by Microsoft– Designed to use existing technologies in servers/browsers

(HTTP redirect, SSL, cookies, Javascript)

Passport

• Client (browser), merchant (Web server), Passport login server

• Passport server maintains authentication info for client – Gives merchant access when permitted by client

• Divides client data into profile (address) and wallet (credit card)

How Passport Works

David P. Kormann and Aviel D. Rubin,Risks of the Passport Single Signon Protocol,Computer Networks, Elsevier Science Press, volume 33, pages 51-58, 2000.

How Passport Works

David P. Kormann and Aviel D. Rubin,Risks of the Passport Single Signon Protocol,Computer Networks, Elsevier Science Press, volume 33, pages 51-58, 2000. SSL

Token = 3DES encrypted authentication infousing key merchant shares with passport serverAlso set cookie at browser (passport)

• User interface is confusing and may misrepresent the reality – user may log out from a server but not from the Passport or vice versa

• Single key is used to encrypt cookies for all clients• Cookies stay on machine, can be stolen

– No authenticator (timestamp) like in Kerberos, enables reuse by others

Some Problems with Passport

David P. Kormann and Aviel D. Rubin,Risks of the Passport Single Signon Protocol,Computer Networks, Elsevier Science Press, volume 33, pages 51-58, 2000.

Read more at http://avirubin.com/passport.html

• Placed into browser cache by servers to store state about this particular user– Contain any information that server wants to remember

about the user as name/value pairs– May contain expiration time– May persist across browser instances

• Returned to server in clear on new access• Only those cookies created for the server’s domain

are sent to the server– May not be created by this server

• Usually used for persistent sign in, shopping cart, user preferences

How Cookies Work

• User logs in using her user/pass– Server sets a cookie with some info – username,

password, session ID …– Any future accesses return this info to the server who

uses it for authentication (equivalent to user/pass)– Once user signs out the cookie is deleted and the session

closed at the server• Problems

– Cookies can be sniffed, remain on the browser because user did not sign out, be stolen by cross-site scripting or via DNS poisoning

• Solutions: – Send cookies over SSL, use timed cookies, secure code,

bind cookies to IP address of the client, encrypt cookies …

Cookies for Authentication

Learn more at: http://cookies.lcs.mit.edu/pubs/webauth:tr.pdf

• Service Provider– Browser goes to Resource Manager who uses

WAYF, and user’s Attribute Requester, and decides whether to grant access.

• “Where are you from” (WAYF) service– Redirects to correct servers

• Federation to form trusted relationships between providers

Federated Identity - Shibboleth

6. I know you now. Redirect to SP, with a

handle for user

8. Based on attribute values, allow access to

resource

Identity Provider(IdP)

Web Site

Service Provider (SP)Web Site

1. User requests resource

2. I don’t know you, or where you are from

LDAP

WAYF

3. Where are you from?

4. Redirect to IdP for your org

5. I don’t know you. Authenticate using your

org’s web login1

2

3

4

5

7

7. I don’t know your attributes. Ask the IdP (peer to peer)

6

ClientWeb Browser

8

Source: Kathryn Huxtable khuxtable@ku.edu 10 June 2005

Shibboleth - Protocol

• Cards– Mag stripe (= password)– Smart card, USB key– Time-varying password

• Issues– How to validate– How to read (i.e. infrastructure)

Something You Have

• Biometrics– Measures some physical attribute

• Iris scan• Fingerprint• Picture• Voice

• Issues– How to prevent spoofing– What if spoofing is possible? No way to obtain new

credentials

Something About You

• Require at least two of the classes we mentioned, e.g.– Smart card plus PIN– RSA SecurID plus password– Biometric and password

Multi-factor Authentication

Authorization and Policy

• Is principal P permitted to perform action A on object O?– Authorization system will provide yes/no answer

Authorization

• Who is permitted to perform which actions on what objects?

• Access Control Matrix (ACM)– Columns indexed by principal– Rows indexed by objects– Elements are arrays of permissions indexed by

action• In practice, ACMs are abstract objects

– Huge and sparse– Possibly distributed

Access Control

Example ACMFile/User Tom Dick Harry

Readme.txt read read read, write

passwords write

Term.exe read, write, execute

• Access Control Lists (ACLs)– For each object, list principals and actions

permitted on that object– Corresponds to rows of ACM

Instantiations of ACMs

File

Readme.txt Tom: read, Dick: read, Harry: read, write

passwords Harry: write

Term.exe Tom: read, write, execute

• Capabilities– For each principal, list objects and actions

permitted for that principal– Corresponds to columns of ACM

• The Unix file system is an example of…?

Instantiations of ACMs

User

Tom Readme.txt: read, Term.exe: read, write, execute

Dick Readme.txt: read

Harry Readme.txt: read, write; passwords: write

• Discretionary• Mandatory • Rule-based• Role-based• Originator-controlled

Types of Access Control

• Owners control access to objects• Access permissions based on identity of

subject/object• E.g., access to health information

Discretionary Access Control

• Rules set by the system, cannot be overriden by owners

• Each object has a classification and each subject has a clearance (unclassified, classified, secret, top-secret)

• Rules speak about how to match categories and classifications– Access is granted on a match

Mandatory Access Control

• Ability to access objects depends on one’s role in the organization

• Roles of a user can change– Restrictions may limit holding multiple roles

simultaneously or within a session, or over longer periods.

– Supports separation of roles• Maps to organization structure

Role-Based Access Control

• Final goal of security– Determine whether to allow an operation

• Depends upon– Policy– Authentication

Authorization

• Policy defines what is allowed and how the system and security mechanisms should act

• Policy is enforced by mechanism which interprets it, e.g.– Firewalls– IDS– Access control lists

• Implemented as– Software (which must be implemented correctly and

without vulnerabilities)

Policy

• Focuses on controlled access to classified information and on confidentiality– No concern about integrity

• The model is a formal state transition model of computer security policy – Describes a set of access control rules which use

security classification on objects and clearances for subjects

• To determine if a subject can access an object– Combine mandatory and discretionary AC (ACM)– Compare object’s classification with subject’s

clearance (Top Secret, Secret, Confid., Unclass.)– Allow access if ACM and level check say it’s OK

Policy models: Bell-LaPadula

• Mandatory access control rules:– a subject at a given clearance may not read an object

at a higher classification (no read-up)– a subject at a given clearance must not write to any

object at a lower classification (no write-down). • Trusted subjects – the “no write-down” rule does

not apply to them– Transfer info from high clearance to low clearance

Policy models: Bell-LaPadula

• Only concerned about integrity– a subject at a given clearance may not write an object

at a higher classification (no write-up)– a subject at a given clearance must not read any

object at a lower classification (no read-down) • Reverse from Bell-LaPadula

– as if content with lower integrity pollutes subjects at higher integrity

Policy models: Biba

• Today’s security tools work with no coordinated policy– Firewalls and Virtual Private Networks– Authentication and Public Key Infrastructure– Intrusion Detection and limited response

• We need better coordination– Not just who can access what, but policy says what

kind of encryption to use, when to notify IDS• Tools should implement coordinated policies

– Policies originate from multiple sources– Policies should adapt to dynamic threat conditions– Policies should adapt to dynamic policy changes

Security > Mix Of Point Solutions

SECURITYAUDIT

RECORDS

GAA: Generic Authentication and Authorization Architecture

INTRUSIONDETECTION

UNDERATTACK

GAA APIEACL

. . .

Authentication

Databases

Web Servers

Firewalls

IPSec

…

• Focus integration efforts on authorization and the management of policies used in the authorization decision– Applications shouldn’t care about authentication or

identity • Separate policy from mechanism

– Authorization may be easier to integrate with applications

– Hide the calls to individual security services• E.g. key management, authentication, encryption, audit

GAA: Integration Through Authorization

• Positive and negative access right• Conditions on each rule - evaluated in a given

order– Pre-conditions

• What must be true in order to grant request– Request-result

• These conditions must be activated regardless of whether the access is granted or not

– Mid-conditions • What must be true during execution of requested

operation– Post-conditions

• What must be true on completion of requested operation.

GAA: Extended ACLs

• From http://gost.isi.edu/info/gaaapi/eacl.html – Tom cannot login to the host– Logins from the specified IP address range are

permitted, using either X509 or Kerberos for authentication if previous login attempts <= 3. If the request fails, the number of the failed logins should be updated. The connection duration < 8 h.

– Anyone, without authentication, can check the status of the host if his IP is in specified range

– Host shut downs are permitted, using Kerberos for authentication. On success, the user ID must be logged. On failure, the sysadmin is sent an e-mail

Sample EACL

Phases of Condition Evaluation

GAA-API

a.isi.edu, connect, Tom

gaa_check_authorization() T/F/U

System State

EACL gaa_get_object_policy_info()

gaa_post_execution_actions() T/F/U

gaa_execution_control() T/F/U

• Dynamic policy evaluation enables response to attacks:– Lockdown system if attack is detected– Establish quarantines by changing policy to establish

isolated virtual networks dynamically– Allow increased access between coalition members

as new coalitions are formed or membership changes to respond to unexpected events

What Dynamic Policies Enable

Scenario - LockDown You have an isolated local area

network with mixed access to web services (some clients authenticated, some not).

Scenario - LockDown You have an isolated local area

network with mixed access to web services (some clients authenticated, some not).

You need to allow incoming authenticated SSH or IPSec connections.

• You have an isolated local area network with mixed access to web services (some clients authenticated, some not).

• You need to allow incoming authenticated SSH or IPSec connections.

• When such connections are active, you want to lock down your servers and require stronger authentication and confidentiality protection on all accesses within the network.

Scenario - LockDown