1 / 45

Chapter 4

Chapter 4. Authentication Applications. Outline. Threat, Vulnerability, Exploit Authentication Applications Kerberos X.509 Authentication Service Recommended reading and Web Sites. What is a threat?.

madaline-osborn
Download Presentation

Chapter 4

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 4 Authentication Applications

  2. Outline • Threat, Vulnerability, Exploit • Authentication Applications • Kerberos • X.509 Authentication Service • Recommended reading and Web Sites

  3. What is a threat? • Threat – any circumstance or event that has potential to cause harm to a system or network. • Threat can be • Internal threat • External threat • It may cause destruction of data and property. • It may involve invasion of privacy

  4. Vulnerability and Exploit ? • Vulnerability – Existence of weakness, design or implementation error that can lead to an unexpected, undesirable event compromising the security of the system. • Exploit – A program or technique that takes advantage of a vulnerability in software or system that can be used for breaking the security and attacking a host over the network.

  5. Internal Threat • Internal threats are threats from with in the organization • These threat originate from individuals who have authorized access to the network or have an account on a server. • It can be from a disgruntled former or current employee or contractor.

  6. Internal Threat • An internal user may attack a system for any number of reasons, including the following: • Data theft • Espionage • Sabotage • General malice • 80% of reported security incidents involved inside abuse (CSI/FBI computer crime and security survey, 2004).

  7. Internal Threat : Sniffing • One of the major internal threat is “sniffing”. • Sniffing – is the process of reading the packets that are transmitted on the network. • Example: • Passwords • Credit card numbers • TELNET, FTP SMTP (e-mail) packets if unencrypted can be successfully sniffed.

  8. External Threat • The threat from outside the organization, who have no legitimate rights to corporate system or information. • External threats like “love bug” can create huge economic losses to corporate company with in a short time. • Types of external threats: • Social Engineering • Denial of Service attack • Virus, Worm and Trojans • Organizational attacks • Accidental security breaches • Automated attacks

  9. Social Engineering • Social engineering • “The act of obtaining unauthorized access to a network by manipulating authorized users in to revealing their passwords and access information.” • Also refer as “People hacking” • Social engineering relies on communication skills. • Social engineering user’s often use telephone to convince. • Social engineering user’s use confidential data or information for unauthorized access to network. • Example of attack: - telephone scams, hoaxes and virus e-mail

  10. Denial of Service attack • DoS is an attack designed to prevent your computer or network from operating or commucating. • Block access to resources • Flood network, degrades performance, causes server to Fail. • Result in • Loss of revenue • Prestige • Service to customer

  11. Authentication Applications • developed to support application-level authentication & digital signatures • will discuss Kerberos – a private-key authentication service • discuss X.509 - a public-key directory authentication service

  12. KERBEROS In Greek mythology, a many headed dog, the guardian of the entrance of Hades

  13. KERBEROS • Authentication service developed as a part of MIT’s Athena project • provides centralized private-key third-party authentication in a distributed network • allows users access to services distributed through network • without needing to trust all workstations • rather all trust a central authentication server

  14. KERBEROS • An open distributed environment • Any user can access services from any workstation • Several security threats exists in such an environment: • A user impersonate another user • A user may change the network address of a w/s and may make it look as another w/s • A user may eavesdrop on a session and mount a replay attack later

  15. KERBEROS : The Requirements • its first report identified requirements as: • secure • reliable • transparent • scalable • implemented using an authentication protocol based on Needham-Schroeder

  16. KERBEROS • Provides a centralized authentication server to authenticate users to servers and servers to users. • Relies on conventional encryption, making no use of public-key encryption • Two versions: version 4 and 5 • Version 4 makes use of DES

  17. Kerberos Version 4 • Terms: • C = Client • AS = authentication server • V = server • IDc = identifier of user on C • IDv = identifier of V • Pc = password of user on C • ADc= network address of C • Kv= secret encryption key shared by AS an V • TS = timestamp • || = concatenation

  18. A Simple Authentication Dialogue • C AS: IDc ||Pc || IDv • AS  C: Ticket • C  V: IDc || Ticket Ticket = EKv[IDc ||Pc || IDv]

  19. Version 4 Authentication Dialogue • Problems: • Lifetime associated with the ticket-granting ticket • If too short  repeatedly asked for password • If too long  greater opportunity to replay • The threat is that an opponent will steal the ticket and use it before it expires

  20. Version 4 Authentication Dialogue Authentication Service Exhange: To obtain Ticket-Granting Ticket • C AS: IDc || IDtgs ||TS1 • AS  C: EKc [Kc,tgs|| IDtgs || TS2 || Lifetime2 || Tickettgs] Ticket-Granting Service Echange: To obtain Service-Granting Ticket (3) C  TGS: IDv ||Tickettgs ||Authenticatorc (4) TGS  C: EKc [Kc,¨v|| IDv || TS4 || Ticketv] Client/Server Authentication Exhange: To Obtain Service (5) C  V: Ticketv || Authenticatorc (6) V  C: EKc,v[TS5 +1]

  21. Overview of Kerberos

  22. Kerberos Realms • a Kerberos environment consists of: • a Kerberos server • a number of clients, all registered with server • application servers, sharing keys with server • this is termed a realm • typically a single administrative domain • if have multiple realms, their Kerberos servers must share keys and trust

  23. Request for Service in Another Realm

  24. Difference Between Version 4 and 5 • Encryption system dependence (V.4 DES) • Internet protocol dependence • Message byte ordering • Ticket lifetime • Authentication forwarding • Interrealm authentication

  25. Kerberos Encryption Techniques

  26. PCBC Mode

  27. Kerberos - in practice • Currently have two Kerberos versions: • 4 : restricted to a single realm • 5 : allows inter-realm authentication, in beta test • Kerberos v5 is an Internet standard • specified in RFC1510, and used by many utilities • To use Kerberos: • need to have a KDC on your network • need to have Kerberised applications running on all participating systems • major problem - US export restrictions • Kerberos cannot be directly distributed outside the US in source format (& binary versions must obscure crypto routine entry points and have no encryption) • else crypto libraries must be reimplemented locally

  28. X.509 Authentication Service • Distributed set of servers that maintains a database about users. • Each certificate contains the public key of a user and is signed with the private key of a CA. • Is used in S/MIME, IP Security, SSL/TLS and SET. • RSA is recommended to use.

  29. X.509 Formats

  30. Typical Digital Signature Approach

  31. Obtaining a User’s Certificate • Characteristics of certificates generated by CA: • Any user with access to the public key of the CA can recover the user public key that was certified. • No part other than the CA can modify the certificate without this being detected.

  32. CA Hierarchy • if both users share a common CA then they are assumed to know its public key • otherwise CA's must form a hierarchy • use certificates linking members of hierarchy to validate other CA's • each CA has certificates for clients (forward) and parent (backward) • each client trusts parents certificates • enable verification of any certificate from one CA by users of all other CAs in hierarchy

  33. X.509 CA Hierarchy

  34. Revocation of Certificates • Reasons for revocation: • The users secret key is assumed to be compromised. • The user is no longer certified by this CA. • The CA’s certificate is assumed to be compromised.

  35. Authentication Procedures • X.509 includes three alternative authentication procedures: • One-Way Authentication • Two-Way Authentication • Three-Way Authentication • all use public-key signatures

  36. One-Way Authentication • 1 message ( A->B) used to establish • the identity of A and that message is from A • message was intended for B • integrity & originality of message • message must include timestamp, nonce, B's identity and is signed by A • may include additional info for B • eg session key

  37. Two-Way Authentication • 2 messages (A->B, B->A) which also establishes in addition: • the identity of B and that reply is from B • that reply is intended for A • integrity & originality of reply • reply includes original nonce from A, also timestamp and nonce from B • may include additional info for A

  38. Three-Way Authentication • 3 messages (A->B, B->A, A->B) which enables above authentication without synchronized clocks • has reply from A back to B containing signed copy of nonce from B • means that timestamps need not be checked or relied upon

  39. Authentication Procedures

  40. X.509 Version 3 • has been recognised that additional information is needed in a certificate • email/URL, policy details, usage constraints • rather than explicitly naming new fields defined a general extension method • extensions consist of: • extension identifier • criticality indicator • extension value

  41. Certificate Extensions • key and policy information • convey info about subject & issuer keys, plus indicators of certificate policy • certificate subject and issuer attributes • support alternative names, in alternative formats for certificate subject and/or issuer • certificate path constraints • allow constraints on use of certificates by other CA’s

  42. Recommended Reading and WEB Sites • www.whatis.com (search for kerberos) • Bryant, W. Designing an Authentication System: A Dialogue in Four Scenes. http://web.mit.edu/kerberos/www/dialogue.html • Kohl, J.; Neuman, B. “The Evolotion of the Kerberos Authentication Service” http://web.mit.edu/kerberos/www/papers.html • http://www.isi.edu/gost/info/kerberos/

More Related