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Mobile Security - Wireless hacking

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Mobile Security - Wireless hacking

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Mobile Security - Wireless hacking

  1. 1. COEN 350 Mobile Security
  2. 2. Wireless Security  Wireless offers additional challenges:  Physical media can easily be sniffed.  War Driving  Legal?  U.S. federal computer crime statute, Title 18 U.S.C. 1030,  Crime to knowingly access a computer used in interstate or foreign communication "without authorization" and obtain any information from the computer.  Crime to access a computer without authorization with "intent to defraud" to obtain "anything of value."  But not if "the object of the fraud and the thing obtained consists only of the use of the computer and the value of such use is not more than $ 5,000 in any 1-year period."
  3. 3. Wireless Security  Wireless offers additional challenges:  Physical media can easily be sniffed.  Mobile computing needs to preserve battery power.  Calculations cost more on a mobile platform.  Especially important for sensor networks
  4. 4. Wireless Security: Attackers Perspective  Knowing the Threat  Targets of opportunity  Goal is  Internet access.  Easy pickings.  Targeted attacks  Targets assets valuable enough.  Internal attackers  Most Dangerous  Can open an unintentional security hole
  5. 5. COEN 351 E-Commerce Security  E-Commerce Security Course Homepage  Lecture Notes
  6. 6. IEEE 802.11  Wired Equivalent Privacy (WEP) Protocol  Based on a shared secret k.  Distributed out of band.  Uses CRC for internal integrity protection.  Uses RC4 to encrypt network traffic.
  7. 7. WEP Protocol
  8. 8. WEP Protocol  Confidentiality  Original packet is first check-summed.  Checksum and data form the payload.  Transmitting device creates a 24-bit random initialization vector IV.  IV and shared key are used to encrypt with RC4
  9. 9. WEP Protocol  RC4  Generates a pseudo-random stream of bytes (keystream)  Based on a secret internal state  Permutation S of all 256 possible bytes  Two index pointers  Plaintext is XORed with keystream
  10. 10. WEP Protocol  RC4  Key Scheduling Algorithm (KSA)  Initializes S based on a key for i from 0 to 255 S[i] := i j := 0 for i from 0 to 255 j := (j + S[i] + key[i mod keylength]) mod 256 swap(S[i],S[j])
  11. 11. WEP Protocol  RC4  Pseudo-Random Generation Algorithm (PRGA)  Generates pseudo-random byte stream i := 0 j := 0 while GeneratingOutput: i := (i + 1) mod 256 j := (j + S[i]) mod 256 swap(S[i],S[j]) output S[(S[i] + S[j]) mod 256]
  12. 12. WEP Protocol  RC4  Known weaknesses  Keystream slightly biased  Fluhrer & McGrew attack can distinguish keystream from random stream given a GB of input.  Fluhrer, Mantin, Shamir: statistics for output of the first few bytes of output keystream are non-random, leaking information about key.
  13. 13. WEP Protocol  Authentication  Station associating with access point needs to authenticate itself.  Both exchange the type of authentication that is accepted.  Open: Just identification between station and AP  Shared Secret: Participants send nonces to each other, encrypt the nonce using WEP (and the shared secret key), and verify the other’s response.
  14. 14. WEP has no key management  Everyone allowed to have access to a wireless network has the same key.  Anyone with the key can read ALL traffic.
  15. 15. WEP: RC4  RC4 uses the key and the IV to produce a stream of pseudo-random bytes.  Calculates cipher text from plaintext by XORing the pseudo-random stream with the plain-text.
  16. 16. WEP: RC4
  17. 17. WEP: Attacks on RC4  Dictionary Attack  Build database:  224 different IVs  Build a database of 224 streams of MTU bytes (2,312 B) for each different IV.  Takes < 40 GB storage.  XOR two entries with the same IV.  Result are the two plaintexts XORed.  Natural language text has enough redundancy to decrypt the XOR of two text streams.
  18. 18. WEP: Attacks on RC4  Dictionary Attack  Many packages can be completely or partially guessed.  XORing guessed plaintext and captured cipher gives pseudo-random byte stream for a given IV.  Some implementations reset IVs poorly.  This simplifies dictionary attacks.
  19. 19. WEP: Attacks on RC4  Injection Attack  Attacker creates packets on the wireless connection.  Attacker XORs plaintext and cipher.  Builds Pseudo-Random Stream database indexed by IV.
  20. 20. RC4 Fluhrer, Mantin, Shamir Attack  First few bits of several thousand messages reveals key.  Based on an analysis of the RC4 code.  Originally kept secret, but later leaked on the internet.
  21. 21. RC4 Fluhrer, Mantin, Shamir Attack  Key Scheduling Algorithm  Sets up RC4 state array S  S is a permutation of 0, 1, … 255  Output generator uses S to create a pseudo-random sequence.  First byte of output is given by S[S[1]+S[S[1]]].  First byte depends on  {S[1], S[S[1], S[S[1]+S[S[1]]}
  22. 22. RC4 Fluhrer, Mantin, Shamir Attack  Key Scheduling Algorithm  First byte of plain text package is part of the SNAP header  0xAA for IP and ARP packages  0xFF or 0xE0 for IPX  Guessing the first byte is trivial  Some IVs are vulnerable: “resolved”  (KeyByte+3, 0xFF, *)  Plus some more  Easy to test whether an IV is vulnerable.  Search for vulnerable IVs.  They leak key bytes probabilistically.  Large number of packets does it.
  23. 23. RC4 Fluhrer, Mantin, Shamir Attack  Optimization needs about 5,000,000 to 1,000,000 packages.  Counter-measures:  Change key frequently.  Change IV counters to avoid bad IVs.
  24. 24. WEP Message Modification  WEP uses CRC code to ascertain integrity of messages.  CRC code is linear:  CRC(x ⊕ y) = CRC(x) ⊕ CRC(y).  Attacker knows plaintext M and desired modification ∆ for target plaintext M’ = M ⊕ ∆.  Attacker want to substitute X = P⊕(M,CRC(M)) for P⊕(M’,CRC(M’)).  Attacker sends X⊕(∆,CRC(∆)) = P⊕(M,CRC(M)) ⊕(∆,CRC(∆)) = P⊕(M’,CRC(M’))
  25. 25. Wireless Insecurity Problems  WiFi card software allows users to change the MAC address.
  26. 26. Wireless Security  Casual user, low yield traffic  WEP is good enough.  Enterprise, Commercial  Combine WEP with higher order security  SSH  VPN  IPSec
  27. 27. WPA  Created by WiFi Alliance  Certification started April 2003  Uses 802.1X authentication server  Distributed different keys to each user.  Can also be used in “pre-shared key” (PSK) mode  Every user uses the same passphrase.  Called WPA Personal
  28. 28. IEEE 802.1X http://www.linux.com/howtos/8021X-HOWTO/index.shtml  Standard for port- based authentication.  Uses a third-party authentication server such as Radius
  29. 29. WPA  Protocol changes over WEP  CRC is replaced by “Michael” MIC.  MIC now includes a frame counter, preventing replay attacks.  Payload bit flipping is now impossible.  Data encryption still uses RC4, but now  Prevents key recovery attacks on WEP by using  128b Key  48b Initialization vector  Temporal Key Integrity Protocol (TKIP) changes key dynamically.
  30. 30. TKIP  Temporal Key Integrity Protocol  Ensures that every data packet has its own encryption key.
  31. 31. 802.11i  Uses AES instead of RC4.  Subset published as WPA2  Uses 802.1X authentication
  32. 32. Protocol Layers  WEP  Privacy only.  Very elementary security.  WPA  Temporal Key Exchange Protocol  Fixes WEP that scrambles keys between packages and adds a secure message check.  AES: Advanced Encryption Standard  802.11i  Military grade encryption, replaces DES  802.1X  General purpose and extensible framework for authentication users and generating / distributing keys.  Simple Secure Network (SSN)  Recipe for authentication based on 802.1X
  33. 33. COEN 351 E-Commerce Security  E-Commerce Security Course Homepage  Lecture Notes

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