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Impersonation Attacks Fred Piper

Impersonation Attacks Fred Piper. Information Security Group Royal Holloway, University of London Egham, Surrey TW20 0EX. Codes & Ciphers Ltd 12 Duncan Road Richmond, Surrey TW9 2JD. Outline. Information security User recognition Use of passwords/PINs/cryptogrphic keys

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Impersonation Attacks Fred Piper

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  1. Impersonation Attacks Fred Piper Information Security Group Royal Holloway, University of London Egham, Surrey TW20 0EX Codes & Ciphers Ltd 12 Duncan Road Richmond, Surrey TW9 2JD

  2. Outline • Information security • User recognition • Use of passwords/PINs/cryptogrphic keys • Use of ‘tokens’ • Phishing • Protection against man-in-the-middle attacks • Multi factor or multi channel? • The use of mobile phones as a ‘token’ for user recognition? Crete - 2007

  3. What is Information Security? Some features include: • Confidentiality • Protecting information from unauthorised disclosure • Integrity • Protecting information from unauthorised modification, and ensuring that information can be relied upon and is accurate and complete • Availability • Ensuring information is available to authorised users when they need it Crete - 2007

  4. Defences and Attacks Defences: • Introduce security mechanism to protect data • Technical • Procedural • Contractual • Introduce strong authentication mechanism Attacks: • Break the technical security mechanism • Impersonate an authorised entity by breaking procedural mechanism Crete - 2007

  5. User Recognition (1) 3 factors: • Something you know (Password/PIN/Cryptographic Key) • Something you own (Token) • Personal characteristic (Biometrics) NOTE: Usually one-way authentication Tokens and biometrics often require ‘readers’ ‘Danger’ of false ‘readers’ Cost issues Crete - 2007

  6. User Recognition (2) • Many systems rely on more than 1 factor • For multi-factor systems compromise of 1 factor should not enable impersonation • The PIN/magnetic stripe card for ATM networks is an example of a 2-factor system where each individual factor is ‘weak’ Crete - 2007

  7. Something You Know • Password • PIN • Cryptographic key Obvious observations: • A PIN is a password with limited alphabet • A cryptographic key may be regarded as a (secret) password which the user may use but probably not know • Policies for the management of PINs and Passwords are inconsistent Crete - 2007

  8. Password Policy It is often recommended that: • Users should adopt a large alphabet (at least alpha- numeric with upper and lower case letters) • Passwords should be long (at least 8 characters?) • Passwords should be randomly generated • Passwords should be different for each system • Passwords should be changed frequently • Passwords should not be written down Crete - 2007

  9. PINs • Personal identification number • Usually 4 digits (sometimes 6) • Reason: users will not be able to remember longer PINs! NOTE: This is inconsistent with general password policy. Undoubtedly a weak password Crete - 2007

  10. Cryptographic Keys • It is the use of a cryptographic key, rather than revealing its value, that identifies a user Crete - 2007

  11. Key establishment channel (secure) Cipher System Cryptogram c Decryption Key Encryption Key Message m Message m Decryption Algorithm Encryption Algorithm Interceptor Crete - 2007

  12. Two Types of Cipher System • Conventional or Symmetric • Decryption Key easily obtained from Encryption Key • Public or Asymmetric • Computationally infeasible to determine Decryption Key from Encryption Key Crete - 2007

  13. Keys as Identifiers • Asymmetric System • Use of the private key acts as an identifier to ‘everyone’ • Symmetric System • Use of a key identifies users only to those (trusted) people who share that key NOTE: If an asymmetric system is used, an impersonator may either 1. obtain the use of the user’s private key 2. substitute their public key for that of the user Crete - 2007

  14. Authentication Using Smart Tokens • Static Password Tokens • Owner authenticates himself to token • Token identified owner to system • Dynamic Password Tokens • Token generates new password • (Owner activates token with PIN) • Owner enters ID plus dynamic password • System knows which dynamic password to accept • Challenge-Response Tokens • System generates challenges • Owner activates token with PIN and enters challenge • Token generates response (probably challenge encrypted with key that is unique to token) • System knows which response to accept Crete - 2007

  15. Dynamic Passwords User’s password changes frequently (possibly at each log-in) Change influenced by at least one of: • Secret information known to user • Intelligent device which is unique to user Crete - 2007

  16. Challenge/Response for Dynamic Password Given an unpredictable challenge, user’s token produces a response which is: • Appropriate to the challenge • Dependent on a user’s token • Dependent on user’s knowledge Crete - 2007

  17. The Challenge / Response Principle for hand-held token USER HOST Challenge PIN-Controlled Random number Key A Key A Response = ? Y/N A - encrypt or OWF Crete - 2007

  18. Impersonation Attacks • 1-way authentication • Steal and/or copy token • Guess or ‘observe’ password/PIN/cryptographic key • Con the user into divulging password/PIN eg phishing • Gain access to device using key • 2-way authentication • Man-in-the-middle Crete - 2007

  19. Phishing Attacks (1) • Social engineering • Attacker discovers secret ‘information known’ • Banking customers have been ‘prime’ targets via email messages and fake websites Crete - 2007

  20. Phishing Attacks (2) Countermeasures • User education/awareness • Use of 2 or 3 factor systems so that compromise of 1 factor has limited impact Crete - 2007

  21. Identification over the Internet • Many applications use 2-factor systems that allow ‘card not present’ transactions • Effectively a physical token is replaced by a virtual token which is nothing more than a card number • This is a 1-factor system • In Singapore the FA mandates use of genuine 2-factor authentication • In UK banks are starting to issue customers with Chip and PIN ‘readers’ Crete - 2007

  22. Phishing • Browsers starting to try to detect fake websites • Google Safe Browsing for Firefox browser • Microsoft’s Internet Explorer 7 • Anti-Phishing War Group (APWG) • Forum to discuss phishing issues and share best practices • www.antiphishing.org Crete - 2007

  23. Phishing Attacks Summary • Enable attacks to discover secret ‘information known’ • ‘Best’ countermeasure is user education/awareness • Effectiveness of attack decreases for 2 or 3 factor systems • Use of conventional 2 or 3 factors often expensive and needs special hardware • Introduction of ‘one-time’ PINs such as ITANs for some German e-banking systems helps Crete - 2007

  24. D-H Man-in-the-Middle Attack B A A’s public key F’s public key F’s public key B’s public key Fraudster F The Fraudster has agreed keys with both A and B Aand B believe they have agreed a common key Crete - 2007

  25. Protection Against Man-in-the-Middle Attack • Rely on TTP to establish key management infrastructure (eg PKI) • Use second (independent) communications channel to confirm key between A and B (Over) Simple Example: • D-H protocol establishes 1024 shared bits • AES key is 128 bits from agreed positions • Users exchange different 32-bit sequences from the 1024 bits over second (possibly insecure) channel Crete - 2007

  26. OOB (Out of Band) Authentication Requirement • A user claims an identity over a computer network • Host wants to use a second channel to confirm it is the genuine user • Neither party is willing to pay for ‘extra hardware’ Crete - 2007

  27. Use of Two Channels • Prior to PK crypto, most cryptographic systems needed a second (secure) channel for initial key establishment • One motivation for introduction of PK crypto Crete - 2007

  28. OOB Communications • Symmetric cryptography • Use secure second channel to enable secure communications over an insecure primary channel • Authentication • Use second (possibly insecure) channel to confirm that the communications over the primary channel are secure NOTE: In this context an insecure channel is one where interception is possible. Crete - 2007

  29. Communications How does ‘token’ communicate with host: • One channel or two channel system? • One-way or two-way authentication? • What is the interface? • The user? • A reader that is part of the network? • Other? Crete - 2007

  30. Mobile Phones • There is a move towards systems where the mobile phone is ‘something you own’ • No reader required • No extra cost (in the sense that most people have them) • Use their own channel • Security implications? Crete - 2007

  31. Question • Are there situations where using the mobile phone as a token in a 2-factor system and using a second communication channel can decrease the chance of successful impersonation attacks? Crete - 2007

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