1. Improving Wireless Privacy with an Identifier-Free Link Layer Protocol Ben Greenstein et.al. MobiSys’08 Presented by Seo Bon Keun

2.  Wired Equivalent Privacy (WEP) Original IEEE 802.11 Encryption : Stream cipher RC4 Integrity : CRC-32 checksum Authentication : Open System / Shared Key Can be cracked within minutes  Deprecated IPSec/SSL tunneling can be used  Wi-Fi Protected Access (WPA) IEEE 802.11i Encryption : CCMP(AES-based) Mode : PSK / EAP IEEE 802.11 and privacy

3.  With MAC address Identify : Who are using networks Location : Who are there? Threat model Eavesdropper Alice (MAC:A) Bob (MAC:B) Charley (MAC:C) Bob (MAC:B) Coffee shop Office

4.  With the pattern of packets Threat model Eavesdropper He may type password ‘please’ He may browse stock pages He may see U-Tube movie clips He may speak in English He is now running Outlook

5.  Attack Inventorying Tracking Profiling  Solution : remove linkability Threat model Eavesdropper Who’s sending packets to whom?

6.  Pseudonym Change MAC addresses each session or when idle Packets can be linked while a MAC address is used Possible solution Eavesdropper Alice (MAC:A) Bob (MAC:B) Charley (MAC:C) Bob (MAC:D) Coffee shop Office Charley (MAC:E) A new guy starts using network! He may be Bob. A new guy starts using network! He may be Bob.

7.  Method s = {A, B, T} header = ElGamal(s, PublicKey B ) Body is encrypted using WPA  Advantage Eavesdropper cannot decipher packet header  Disadvantage Every packets should be deciphered Performance drops! Straw Man

8. Solution : SlyFi ClientAP 802.11 Probe request Probe reply Authentication request Authentication reply Association request Association reply Data Acknowledgements ClientAP SlyFi Tryst(probe req.) Tryst(probe rep.) Tryst(auth. req.) Tryst(auth. rep.) Shroud(assoc. req.) Shroud(Data) Shroud(Acks) Shroud(assoc. rep.) Discovery & Binding Data Transport

9.  Infrequent communication!  Long-term unlinkability Two packets sent on different time period(I), cannot be linked to  A, B knows and T 0  Temporary address for time T  Generate random key k p SlyFi - Tryst Tryst Header Tryst Body

10.  Connected Communication Has starting key for the communication! Create unlinkable addresses for every packets  A, B knows  Per-packet unlinkable addresses SlyFi - Shroud Shroud Header Shroud Body

11.  Tryst Clock skew Create addresses from T i-k to T i+k Forward security Compute new key for each day  Shroud Packet loss Create w consecutive addresses  Coexistence SlyFi can coexist with 802.11 devices SlyFi – Additionals

12.  Link setup time Performance evaluation

13.  Data transport performance Performance evaluation

14.  Identifier free 802.11 link layer protocol  Tries to achieve higher level of privacy protection without losing performance  Comparable to IEEE 802.11w Increase the security of the management frames Conclusion

15. Q&A