Usable Bootstrapping of Secure Ad Hoc Communication Ersin Uzun PARC 1

Outline What is first connect (aka device pairing or bootstrapping secure communication)? Why is it hard to secure? Why usability is important? Methods & standards, and the current state. 2

Secure pairing of personal devices Pairing: bootstrapping the association and the security contexts for subsequent communication. E.g., Pairing a bluetooth phone and a headset Enrolling a phone or PC into a home WLAN 3

4 What devices? Desktops Laptops PDAs Phones MP3 Players Wireless Headsets Cameras Device (e.g., TV) Remotes Access Points FAX-s/Copiers/Printers Sensors? RFIDs? Pacemakers? Dialysis devices?

Setting up a security association (authenticated secure communication) where: no prior context exists (no PKI, common TTPs, key servers, shared secrets, etc.) Ordinary non-expert users Cost-sensitive commodity devices Problem Ohh! I cannot even pair my socks! 5

Wireless channel: susceptible to eavesdropping Lets use K as the secret key Alice Bob OK 6 Encrypted Communication using K

Uups! Lets use K as the secret key Alice Bob OK Eve can decrypt the communication! Eve can impersonate either party! 7 Communication

Also open to active attacks… PK E1 Eve PK A Alice Bob PK E2 PK B Man in the middle attack over Diffie-Hellman key agreement 8

Mechanisms should be intuitive...and work on various devices! SSID? WPA? Passcode! Which E61? 9

… and secure 10

Security and usability coexistence Better usability = insecure? More security = harder to use? 11

Goal: Secure, intuitive, inexpensive methods for secure communication bootstrapping One well-studied approach: using two communication channels Assumption: Peer devices are physically identifiable Two channels: 1. Wireless channel 2. OOB channel: Human perceivable or location-limited Other approaches Based on physical properties of wireless signals Distance-bounding Environmental sensing 12

Some examples (not a complete list!) Various OOB channels Cables Resurrecting Duckling, [Stanajo, et al. IWSP99] Camera, barcodes/LEDs Seeing-is-believing, [McCune, et al. S&P05] SIB revisited, [Saxena, et al. S&P06] GAnGS, [Chen, et al. Mobicom08] SPATE, [Lin, et al. Mobisys09] Speakers and microphones Loud And Clear, [Goodrich, et al. ICDCS06) HAPADEP, [Soriente, et al. ISC08) Other hardware Accelerometers Shake well before use, [Mayrhofer, et al. Pervasive07] Ultrasound, laser transceivers and many others.... Standardization activities Wi-fi protected setup Bluetooth secure pairing Wireless USB association models Location limited channels IrDA: Talking to Strangers, [Balfanz, et al. NDSS02] NFC: Bluetooth specs draft Distance-bounding (e.g., Capkun et al. TMC10), Env. sensing (Krumm et al. Ubicomp07) 13

Where are we now? Proposals are not adapted by manufacturers I still cannot securely pair a Bluetooth handset and a phone in the presence of an active attacker My mother still cannot secure her WLAN at home without my help Emerging scenarios are even more challenging Group pairing Home sensor networks Pairing with personal RFID tags 14

Thanks! 15