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Key Exchange – Diffie-Hellman – Symmetric crypto (KDC idea, Needham-Shroeder, Kerberos) – Asymmetric crypto – certificates Stolen keys recovery Group keys.

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Presentation on theme: "Key Exchange – Diffie-Hellman – Symmetric crypto (KDC idea, Needham-Shroeder, Kerberos) – Asymmetric crypto – certificates Stolen keys recovery Group keys."— Presentation transcript:

1 Key Exchange – Diffie-Hellman – Symmetric crypto (KDC idea, Needham-Shroeder, Kerberos) – Asymmetric crypto – certificates Stolen keys recovery Group keys Authentication – Something you know (passwords, handle storage, handle network transmission) – Something you have, something about you Summary From the Last Lecture

2 Passport Liberty Alliance Shibboleth Single Sign-On

3 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 v1

4 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.

5 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, SSL Token = 3DES encrypted authentication info using key merchant shares with passport server Also set cookie at browser (passport)

6 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

7 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:

8 User interface is confusing and may misrepresent the reality – user may log out from a server but not from the Passport or vice versa Weak keys may be used for 3DES 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, Read more at

9 Multiple federated identity providers – E.g. ISPs register own users – One can rely on claims made by other ID providers Claims – s, relationships, authorization for scenarios, ownership of private/public key pair Need “translators” for different claim languages Federated Passport

10 Similar to Federated Passport, i.e. no central authority Use SAML (Security Association Markup Language) to describe trust across authorities, and what assertions mean from particular authorities Four assurance levels – How much we trust a given identity assertion – Little, some, high and very high confidence Liberty Alliance

11 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

12 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 login I don’t know your attributes. Ask the IdP (peer to peer) 6 Client Web Browser 8 Source: Kathryn Huxtable 10 June

13 Common API for client-server authentication Standard interface for choosing among authentication methods – Once an application uses GSS-API, it can be changed to use a different authentication method easily No code rewriting required Dominant implementation is Kerberos – Some procedure calls Acquire and release credentials Manage security context – Init, accept, and process tokens (challenges) Wrap and unwrap (encrypt/decrypt) Generic Security Services API Moving up the Stack

14 Brute force Dictionary Guessing Finding elsewhere Attacks on Password Authentication

15 Cards – Mag stripe (= password) – Smart card, USB key – Time-varying password Issues – How to validate – How to read (i.e. infrastructure) Something You Have

16 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

17 IP Address Caller ID (or call back) Past transaction information – Example of something you know Other Forms Of Authentication

18 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

19 Authorization and Policy

20 Determining permission – Is principal P permitted to perform action A on object U? Adding permission – P is permitted to perform action A on object U In this course, we use the first definition Authorization: Two Meanings

21 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

22 Example ACM File/UserTomDickHarry Readme.txtread read, write passwordswrite Term.exeread, write, execute

23 Access Control Lists (ACLs) – For each object, list principals and actions permitted on that object – Corresponds to rows of ACM Instantiations of ACMs File/User Readme.txtTom: read, Dick: read, Harry: read, write passwordsHarry: write Term.exeTom: read, write, execute

24 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 TomReadme.txt: read, Term.exe: read, write, execute DickReadme.txt: read HarryReadme.txt: read, write; passwords: write

25 Permissions may need to be determined dynamically – Time – System load – Relationship with other objects – Security status of host Distributed nature of systems may aggravate this – ACLs need to be replicated or centralized – Capabilities don’t, but they’re harder to revoke Problems

26 Discretionary Mandatory Rule-based Role-based Originator-controlled Types of Access Control

27 Owners control access to objects Access permissions based on identity of subject/object E.g., access to health information Discretionary Access Control

28 Rules set by the system, cannot be overriden by owners Each object and subject has a category and a classification Rules speak about how to match categories and classifications – Access is granted on a match Mandatory Access Control

29 Individual subjects are granted access to objects if allowed by rules Rules are set by the system administrator Rule-Based Access Control

30 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

31 Creator of an object decides who will access it E.g., owner can listen to a song but cannot share it with others Originator-Based Access Control

32 Final goal of security – Determine whether to allow an operation Depends upon – Policy – Authentication – Other characteristics Authorization

33 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) The Role Of Policy

34 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

35 Three security properties: – Simple Security Property - a subject at a given security level may not read an object at a higher security level (no read-up) – Star Property - a subject at a given security level must not write to any object at a lower security level (no write-down). Strong Star Property – only write to same level – The Discretionary Security Property - discretionary access control specified via an access control matrix Trusted subjects - no star property rule – Transfer info from high clearance to low clearance Policy models: Bell-LaPadula

36 Like Bell-LaPadula but speaks about integrity Cannot write to higher-level objects Subject’s integrity drops if it reads a lower-level object Policy Models: Biba

37 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

38 SECURITY AUDIT RECORDS GAA: Generic Authentication and Authorization Architecture INTRUSION DETECTION UNDER ATTACK GAA API EACL... Authentication Databases Web Servers Firewalls IPSec …

39 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

40 Positive and negative access right Conditions on each rule - evaluated in a given order Sample ACL ( ) – 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 GAA: Extended ACLs

41 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: Conditions

42 Three 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

43 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

44 Scenario - LockDown  You have an isolated local area network with mixed access to web services (some clients authenticated, some not).

45 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.

46 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

47 Malicious Code

48 Disclaimer Some techniques and tools mentioned in this class could be: – Illegal to use – Dangerous for others – they can crash machines and clog the network – Dangerous for you – downloading the attack code you provide attacker with info about your machine Don’t use any such tools in real networks – Especially not on USC network – You can only use them in a controlled environment, e.g. DETER testbed Dangerous

49 Intrusions Why do people break into computers? What type of people usually breaks into computers? I thought that this was a security course. Why are we learning about attacks?


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