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Lecture 12 Mobile Networks: Security in Wireless LANs and Mobile Networks

Wireless Networks and Mobile Systems. Lecture 12 Mobile Networks: Security in Wireless LANs and Mobile Networks. Lecture Objectives. Introduce security vulnerabilities and defenses Describe security functions in Basic mechanisms WiFi Protected Access (WPA) IEEE 802.11i

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Lecture 12 Mobile Networks: Security in Wireless LANs and Mobile Networks

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  1. Wireless Networks and Mobile Systems Lecture 12Mobile Networks: Security inWireless LANs and Mobile Networks

  2. Lecture Objectives • Introduce security vulnerabilities and defenses • Describe security functions in • Basic mechanisms • WiFi Protected Access (WPA) • IEEE 802.11i • Describe some other security issues Mobile Networks: Security in Wireless LANs and Mobile Networks 2

  3. References • J. F. Kurose and K. W. Ross, Computer Networking: A Top-Down Approach Featuring the Internet, 2nd ed., Addison Wesley, 2003, Chapter 7. • T. Karygiannis and L. Owens, “Wireless Network Security: 802.11, Bluetooth, and Handheld Devices,” NIST Special Publication 800-48, Nov. 2002. • http://csrc.nist.gov/publications/nistpubs/800-48/NIST_SP_800-48.pdf • WiFi Protected Access (WPA) • http://www.wi-fi.org/OpenSection/protected_access.asp Mobile Networks: Security in Wireless LANs and Mobile Networks 3

  4. Agenda • Security vulnerabilities and objectives • Security mechanisms • Basic security features in IEEE 802.11 • Improving WLAN security • Augmenting WLAN security • Other security issues Mobile Networks: Security in Wireless LANs and Mobile Networks 4

  5. Wireless Magnifies Exposure Vulnerability • Information going across the wireless link is exposed to anyone within radio range • RF may extend beyond a room or a building • Infrared limited to a room • Traditional wireline networks benefit from physical security • Access to the wire is required to gain information • Switched networks further reduce exposure Sniffing is easy Mobile Networks: Security in Wireless LANs and Mobile Networks 5

  6. Mobility Makes it Difficult toEstablish Trust • A mobile user must connect to a network component (e.g., an access point) that is physically hidden • Problem on both home and foreign networks • Mobility on foreign networks -- service providers are unknown and, perhaps, not trusted • Access points • Foreign agents • DHCP servers Is this my AP? Mobile Networks: Security in Wireless LANs and Mobile Networks 6

  7. Lack of Infrastructure • Lack of security infrastructure • Authentication servers • Certificate authorities • Unknown nodes providing service • Intermediate nodes for ad hoc routing Can intermediatenode be trusted? Mobile Networks: Security in Wireless LANs and Mobile Networks 7

  8. System Design Issues • Mobile form factor • Desire low power consumption • Minimize computation • Minimize network communication • Constrained by low processing capabilities • Constrained by limited link capacity • Need cryptographic and other security-related algorithms to be simple • Need to minimize communications overhead for security protocols Mobile Networks: Security in Wireless LANs and Mobile Networks 8

  9. Secure Communications (1) • Privacy or confidentiality • The intended recipients know what was being sent but unintended parties cannot determine what was sent • Requires some form of encryption and decryption • Encryption at the sender • Decryption at the receiver using a public or private (secret) key to decode the encrypted information • Authentication • Confirms the identity of the other party in the communication • Assures that • The claimed sender is the actual sender • The claimed receiver is the actual receiver Mobile Networks: Security in Wireless LANs and Mobile Networks 9

  10. Secure Communications (2) • Message integrity and non-repudiation • Data integrity – data is transmitted from source to destination without undetected alteration • Non-repudiation – prove that a received message came from a claimed sender • Availability and access control • Ensures availability of resources for the intended users • Controls access to resource Mobile Networks: Security in Wireless LANs and Mobile Networks 10

  11. Link Versus End-to-End Security • End-to-end security • Provided by network (e.g., IPsec), transport (e.g., SSL), and/or application layer (e.g., application-specific) • Link security • Provided by link layer (e.g., IEEE 802.11 WEP, WPA, or IEEE 802.11i) End-to-End Security Link Security Mobile Networks: Security in Wireless LANs and Mobile Networks 11

  12. Security Objectives (1) • Major concerns at the link layer • Authentication (but, related to access control) • Privacy • Integrity • Major concerns at the network layer (e.g., IPsec) • Authentication • Privacy • Integrity Mobile Networks: Security in Wireless LANs and Mobile Networks 12

  13. Security Mechanisms (2) • Security mechanisms at the transport layer (e.g., SSL) and in applications may deal with all objectives • Authentication • Privacy • Integrity • Access control Mobile Networks: Security in Wireless LANs and Mobile Networks 13

  14. Agenda • Security vulnerabilities and objectives • Security mechanisms • Basic security features in IEEE 802.11 • Improving WLAN security • Augmenting WLAN security • Other security issues Mobile Networks: Security in Wireless LANs and Mobile Networks 14

  15. Cryptography • Symmetric (private) key cryptography • Sender and receiver keys are identical (KA = KB) • Asymmetric (public) key cryptography • Sender (encryption) key (KA) is public • Receiver (decryption) key (KB KA) is private Plaintext KA Ciphertext KB Plaintext Encryption Decryption Mobile Networks: Security in Wireless LANs and Mobile Networks 15

  16. Public Key Cryptography • Unlike a private key system, one can publish the key for encryption in a public key encryption system KB+ Public key Private key Plaintext Ciphertext KB- Plaintext Encryption Decryption m KB+(m) m = KB-(KB+(m)) Mobile Networks: Security in Wireless LANs and Mobile Networks 16

  17. Authentication withPrivate Key Cryptography • Authentication can be implemented with symmetric (private) key cryptography A B Claim “A” Generate aone-time “nonce” R encrypt decrypt K(R)  R Mobile Networks: Security in Wireless LANs and Mobile Networks 17

  18. Authentication withPublic Key Cryptography • Use of public key avoids shared key problem • Vulnerable to “man-in-the-middle” attack A B Claim “A” KA+: A’s public key KA-: A’s private key R KA-(R) Sender must have used private key of A, so it is A Key Request KA+  Compute KA+(KA-(R)) = R Mobile Networks: Security in Wireless LANs and Mobile Networks 18

  19. Agenda • Security vulnerabilities and objectives • Security mechanisms • Basic security features in IEEE 802.11 • Authentication • Privacy • Improving WLAN security • Augmenting WLAN security • Other security issues Mobile Networks: Security in Wireless LANs and Mobile Networks 19

  20. IEEE 802.11 Security • Security was not thoroughly addressed in the original IEEE 802.11 standard • Based on Wired Equivalent Privacy (WEP) • Objective is to not compromise security when compared to a standard wired LAN (e.g., Ethernet) – but what does this really mean? • Evolution • Long-term: IEEE 802.11i • Short-term: WiFi Protected Access (WPA) Mobile Networks: Security in Wireless LANs and Mobile Networks 20

  21. IEEE 802.11: Authentication (1) • IEEE 802.11 supports two authentication schemes • Open system “authentication” • Shared key authentication • Authentication management frames used in a transaction to establish authentication • Authentication algorithm number • Authentication transaction sequence number • Status code • Deauthentication management frame sent to terminate an association • Reason code Mobile Networks: Security in Wireless LANs and Mobile Networks 21

  22. IEEE 802.11: Authentication (2) • Open system “authentication” is really just a placeholder for systems that do not wish to implement true authentication • One station asserts its identity • The other station responds with success • Shared key authentication • Both stations must have a copy of a WEP key • Station proves identity by encrypting and returning challenge text • 128-bit challenge text based on RC4 stream cipher • Shared key authentication only authenticates the station to the AP, not the AP to the station! Mobile Networks: Security in Wireless LANs and Mobile Networks 22

  23. IEEE 802.11: Shared Key Authentication • Uses private key authentication scheme shown earlier STA AP identity assertion 128-bitone-time nonce identity assertion/challenge text Encrypted using shared WEP key encrypted text Decrypted using shared WEP key success/failure Mobile Networks: Security in Wireless LANs and Mobile Networks 23

  24. IEEE 802.11: Deauthentication • A station can terminate an authentication association with another station by sending that station a deauthentication frame • Contains just a reason code, e.g., sending station is leaving the BSS or ESS Mobile Networks: Security in Wireless LANs and Mobile Networks 24

  25. IEEE 802.11: Privacy • Based on Wired Equivalent Privacy (WEP) • MAC at sender encrypts frame body of data frames • Headers and non-data frames are not encrypted • Does not protect against data analysis attacks • MAC at receiver decrypts and passes data to higher level protocol • Uses RC4 symmetric stream cipher • Same key at sender and receiver • Can be applied to variable length data • Key distribution not addressed in standard Mobile Networks: Security in Wireless LANs and Mobile Networks 25

  26. WEP Data Encryption • Host/AP share 40-bit symmetric key • Semi-permanent WEP key • May be longer (e.g., 128 bits) • Host appends 24-bit initialization vector (IV) for each frame to create a 64-bit key • 152-bit key with 128-bit WEP key • The 64-bit key is used to generate a stream of keys, kiIV , using RC4 private key stream cipher algorithm • Key kiIV is used to encrypt byte i, di, in the frame • ci = di XOR kiIV (XOR is exclusive-or) • Initialization vector (IV) and the encrypted bytes, ci, are sent in the frame Mobile Networks: Security in Wireless LANs and Mobile Networks 26

  27. WEP Encryption at the Sender KS Key Sequence Generator KS = shared WEP key IV … … k1IV k2IV kNIV kN+1IV kN+4IV … … d1 d2 dN crc1 crc4 Supports integrity      … … c1 c2 cN cN+1 cN+4 802.11Header IV WEP-encrypted data and CRC Mobile Networks: Security in Wireless LANs and Mobile Networks 27

  28. WEP Encryption Vulnerability • Initialization vectors are 24 bits in length and a new one is used each frame, so IVs are eventually reused • IVs are transmitted in plaintext, so IV reuse can be detected just by packet sniffing • Attack • An intruder causes a host to encrypt known plaintext, d1, d2, d3,… • The intruder sees ci = di XOR kiIV • The intruder knows ci and di, so it can compute kiIV • The intruder knows encrypting key sequence k1IV, k2IV, k3IV, k4IV, … • The next time that the same IV is used, the intruder can decrypt Mobile Networks: Security in Wireless LANs and Mobile Networks 28

  29. IEEE 802.11: Security Weaknesses (1) • WEP encryption is flawed, affecting privacy and authentication • Static WEP keys leave encryption vulnerable • Initialization vectors sent in the clear • Generation of IVs may be weak • Not specified in the standard • All NICs from a vendor may generate the same sequence of IVs or the IV may be a fixed value • Exposed IV (revealing part of key) plus weakness of RC4 make WEP vulnerable to analysis • Can be broken for a busy network by a contemporary personal computer – about 10 hours for sniffing and a few seconds to “guess” the key Mobile Networks: Security in Wireless LANs and Mobile Networks 29

  30. IEEE 802.11: Security Weaknesses (2) • Integrity check based on CRC • Relatively weak compared to a hash or message authentication scheme • Introduces vulnerabilities for certain kinds of attacks • Unilateral challenge-response used for authentication vulnerable to “man-in-the-middle” attack • Asymmetric authentication • Station cannot authenticate AP • Key management is not addressed by the standard • Very complex task, especially for a large network Mobile Networks: Security in Wireless LANs and Mobile Networks 30

  31. IEEE 802.11: Security Weaknesses (3) • “Out-of-the-box” default is usually no security • Ease of deployment and ease of operation for users • Lots of WLANs with no security configured! Mobile Networks: Security in Wireless LANs and Mobile Networks 31

  32. Agenda • Security vulnerabilities and objectives • Security mechanisms • Basic security features in IEEE 802.11 • Improving WLAN security • Augmenting WLAN security • Other security issues Mobile Networks: Security in Wireless LANs and Mobile Networks 32

  33. Improving IEEE 802.11 Security • RSA Security’s Fast Packet Rekeying • WiFi Alliance’s WiFi Protected Access (WPA) • IEEE 802.11 Technical Group i (IEEE 802.11i) Mobile Networks: Security in Wireless LANs and Mobile Networks 33

  34. Fast Packet Rekeying • Generates a unique key to encrypt each network packet on the WLAN • Hashing technique used to rapidly generates per packet keys • The IEEE 802.11 group has approved fast packet rekeying as a fix for WEP security weaknesses Mobile Networks: Security in Wireless LANs and Mobile Networks 34

  35. WiFi Protected Access • WiFi Protected Access (WPA) is intended as a near-term solution to the IEEE 802.11 security problem • Software-only updates – requires update to AP firmware and NIC driver • A subset of the more extensive IEEE 802.11i techniques • Based on two main functions • 802.1x port-based access control • Temporal Key Integrity Protocol (TKIP) Mobile Networks: Security in Wireless LANs and Mobile Networks 35

  36. IEEE 802.1x Port-Based Access Control • Allows use of upper-layer authentication protocols • AP and station can authenticate each other • Integrates with IETF’s Extensible Authentication Protocol (EAP) • See RFC 2284 • Authentication can be… • On the AP • Use a backend server, e.g., with RADIUS • Allows use of session keys • 802.1x keys can be changed each session • Standard WEP keys are semi-permanent Mobile Networks: Security in Wireless LANs and Mobile Networks 36

  37. Temporal Key Integrity Protocol • Extends the initialization vector (IV) space beyond 24 bits • Uses key construction for each packet • Improves cryptographic integrity check beyond CRC used in WEP • Supports key derivation and distribution Mobile Networks: Security in Wireless LANs and Mobile Networks 37

  38. IEEE 802.11i • IEEE 802.11i also known as Robust Security Network (RSN) • Longer-term solution (but should be available very soon) • Requires hardware replacements for APs and NICs • Superset of WPA – includes… • IEEE 802.1x port-based access control • Temporal Key Integrity Protocol (TKIP) • Includes support for Advanced Encryption Standard (AES) for confidentiality and integrity Mobile Networks: Security in Wireless LANs and Mobile Networks 38

  39. Advanced Encryption Standard • The Advanced Encryption Standard (AES) is published by NIST as the successor to Data Encryption Standard (DES) • Operation • 128-byte blocks of data (cleartext) • 128-, 192-, or 256-bit symmetric keys • NIST estimates that a machine that can break 56-bit DES key in 1 second would take about 149 trillion years to crack a 128-bit AES key (unless someone is very lucky) Mobile Networks: Security in Wireless LANs and Mobile Networks 39

  40. Agenda • Security vulnerabilities and objectives • Security mechanisms • Basic security features in IEEE 802.11 • Improving WLAN security • Augmenting WLAN security • Other security issues Mobile Networks: Security in Wireless LANs and Mobile Networks 40

  41. Mitigating Risk* • Management countermeasures • For example, standardizing AP settings and controlling use of WLANs within an organization • Operational countermeasures • For example, controlling coverage area of APs • Technical countermeasures • Access point configuration • Firmware and software updates • Personal firewalls • Intrusion detection systems (IDS) • Maximizing WEP key length • Security audits • Virtual private networks *Karygiannis and Owens, 2002 Mobile Networks: Security in Wireless LANs and Mobile Networks 41

  42. Virtual Private Networks • Using a VPN (e.g., based on IPsec) above the WLAN provides the security present in the environment of the VPN server VPN Tunnel Link Security VPNServer Mobile Networks: Security in Wireless LANs and Mobile Networks 42

  43. Agenda • Security vulnerabilities and objectives • Security mechanisms • Basic security features in IEEE 802.11 • Improving WLAN security • Augmenting WLAN security • Other security issues Mobile Networks: Security in Wireless LANs and Mobile Networks 43

  44. Bluetooth • While generally more secure than IEEE 802.11, there are vulnerabilities • More information… • C. T. Hager and S. F. Midkiff, “Demonstrating Vulnerabilities in Bluetooth Security,” IEEE Global Telecommunications Conference (GLOBECOM), Vol. 3, Dec. 1-5, 2003, pp. 1420-1424. • C. T. Hager and S. F. Midkiff, “An Analysis of Bluetooth Security Vulnerabilities,” IEEE Wireless Communications and Networking Conference, Vol. 3, March 16-20, 2003, pp. 1825-1831. Mobile Networks: Security in Wireless LANs and Mobile Networks 44

  45. Mobile Networks • Security vulnerabilities in Mobile IP • Rogue Foreign Agents • Impersonating a Home Agent • Impersonating a Mobile Host to redirect traffic • Reducing security to enable Mobile IP – router at foreign network • Security vulnerabilities in mobile ad hoc networks (MANETs) • Generating faulty routing information • Snooping on relayed traffic • Refusing to route • Power-oriented attacks Mobile Networks: Security in Wireless LANs and Mobile Networks 45

  46. Summary • Examined the basic objectives of security and fundamental approaches to cryptography and authentication • IEEE 802.11 security features (which are flawed) • Authentication • Privacy and integrity • Solutions to IEEE 802.11’s security problems • WiFi Protected Access (WPA) • IEEE 802.11i – Robust Security Network (RSN) • Higher layer security methods can also address WLAN security problems • Other security issues in wireless and mobile systems Mobile Networks: Security in Wireless LANs and Mobile Networks 46

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