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Cryptography and Network Security 1 CS549: Cryptography and Network Security © by Xiang-Yang Li Department of Computer Science, IIT
Cryptography and Network Security 1
CS549:Cryptography and Network Security
© by Xiang-Yang Li
Department of Computer Science, IIT
Cryptography and Network Security 2
Notice©This lecture note (Cryptography and Network Security) is prepared by
Xiang-Yang Li. This lecture note has benefited from numerous textbooks and online materials. Especially the “Cryptography and Network Security” 2nd edition by William Stallings and the “Cryptography: Theory and Practice” by Douglas Stinson.
You may not modify, publish, or sell, reproduce, create derivative works from, distribute, perform, display, or in any way exploit any of the content, in whole or in part, except as otherwise expressly permitted by the author.
The author has used his best efforts in preparing this lecture note. The author makes no warranty of any kind, expressed or implied, with regard to the programs, protocols contained in this lecture note. The author shall not be liable in any event for incidental or consequential damages in connection with, or arising out of, the furnishing, performance, or use of these.
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Cryptography & Network Security
Wireless LAN SecurityRoad to 802.11i
Xiangyang Li
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ContentsIntroductionProblem: 802.11b Not Secure!Wired Equivalent Privacy – WEPTypes of Attacks802.11b Proposed Solutions802.1XWi-Fi Protected Access (WPA)802.11i: The SolutionConclusion
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Introduction
Popular in offices, homes and public spaces (airport, coffee shop)Most popular: 802.11b
Example: Yahoo! DSL Wireless KitTheoretical max @ 11MbpsOperate at 2.4GHz bandDSSS/FSSS modulation – similar to CDMA phones
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Introduction
Standards: IEEE 802.11 Series802.11b – 11Mbps @ 2.4GHz802.11a – 54Mbps @ 5.7GHz band802.11g – 54Mbps @ 2.4GHz band802.1X – security add-on802.11i – high security
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Problem: 802.11b Not Secure!
“No inherent security”Wired Wireless media change was the objective
Wired Equivalent Privacy (WEP)The only “security” built into 802.11Uses RC4 Stream Cipher – in a bad wayVulnerable to several types of attacks
Sometimes not even turned ON
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Wired Equivalent Privacy – WEP
RC4 stream cipherDesigned by Ron Rivest for RSA SecurityVery simple
Initialization Vector (IV)Shared Key
The issue is in the way RC4 is usedIV (24 bits) reuse and fixed keyEarly versions used 40-bit key128-bit mode effectively uses 104 bits
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Wired Equivalent Privacy – WEP
RC4 Key Stream Encryption (source: http://mason.gmu.edu/~gharm/wireless.html)
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Types of Attacks
AttacksConfidentialityIntegrityAvailability
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Types of Attacks
Attacks on ConfidentialityTraffic AnalysisPassive Eavesdropping
Very easy to doActive EavesdroppingUnauthorized Access
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Types of Attacks
Attacks on Confidentiality and/or Integrity
Man-In-The-MiddleAttacks on Integrity
Session HijackingReplay
Attacks on AvailabilityDenial of Service
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802.11b Proposed Solutions
Virtual Private NetworkClosed Network
Through the use of SSIDEthernet MAC address control listsReplace RC4 with block cipherDon’t reuse IVAutomatic Key Assignment
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802.1X: Interim Solution
Port-based authenticationNot specific to wireless networks
Authentication serversRADIUS
Client authenticationEAP
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802.1X Problems
802.1X still has problemsExtensible Authentication Protocol (EAP)
One-way authenticationAttacks
Man-in-MiddleSession Hijacking
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802.1X Proposed Solutions
Per-packet authenticity and integrityLots of overhead
Authenticity and integrity of EAPOL messagesTwo-way authentication
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Wi-Fi Protected Access (WPA)
Addresses issues with WEPKey management
TKIPKey expansion
Message Integrity CheckSoftware upgrade onlyCompatible with 802.1XCompatible with 802.11i
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802.11i
Finalized: June, 2004Robust Security NetworkWi-Fi Alliance: WPA2Improvements made
Authentication enhancedKey Management createdData Transfer security enhanced
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802.11i - Authentication
Authentication ServerTwo-way authentication
Prevents man-in-the-middle attacksMaster Key (MK)Pairwise Master Key (PMK)
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802.11i – Key Management
Key TypesPairwise Transient KeyKey Confirmation KeyKey Encryption KeyGroup Transient KeyTemporal Key
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802.11i – Key Management
Source: http://csrc.nist.gov/wireless/S10_802.11i%20Overview-jw1.pdf
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802.11i – Data Transfer
CCMPLong term solution – mandatory for 802.11i complianceLatest AES encryptionRequires hardware upgrades
WRAPProvided for early vendor support
TKIPCarried over from WPA
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802.11i – Additional Enhancements
Pre-authenticationRoaming clients
Client ValidationPassword-to-key mappingsRandom number generation
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Conclusion
Basic 802.11b (with WEP)Massive security holesEasily attacked
802.1XGood interim solutionAllows use of existing hardwareCan still be attacked
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Conclusion
Wi-Fi Protected AccessAllows use of existing hardwareCompatible with 802.1XCompatible with 802.11i
802.11iMay require hardware upgradesVery secureNothing is ever guaranteed
