K21 and Automation System Architecture Matthew Burnside MIT Laboratory for Computer Science January 8, 2002 Jointly with: Dwaine Clarke, Todd Mills, Ali Tariq

Overview Problem Naïve Solution Our Solution 3 Layers 2 Protocols Device-Proxy protocol Proxy-Proxy protocol

Problem Description Camera Lamp Coffee Maker Printer ? How to interconnect securely?

Security Goals Identification and authentication of resources What is this thing, and is it really what it says it is? E.g., printers, light bulbs, speakers, coffee makers, etc. Secure communication with resources E.g., I don’t want anyone to know I am watching “Jerry Springer” Provide usage/access permissions Access Control Lists (ACLs) for most resources

The Naïve Solution Each device has a public key/private key pair. Communication to the device is encoded with its public key – And signed with private key of initiator Each transaction goes through a server Servers maintain ACLs for each device. – Centralized, secure server handles all the traffic

Issues to Remember Devices are dumb. – No public-key crypto on a light bulb. Centralization is not necessarily a good idea – Problems with scalability and fault tolerance. – Makes ACL maintenance difficult.

Three layers Modular architecture – Layers can be implemented differently without affecting others Our System Security Routing and Naming Device communication Scripting

Event-Based Communication All messages are passed in the form of events.

Layer 1: Device Communication Device Wireless Transceiver Device Wireless Transceiver Device Wireless Transceiver Ethernet Card Wireless Transceiver Proxy A device may also contain a Cricket listener. UDP/IP One proxy for every device. Each device may have a unique interface to its proxy. Gateway

Proxy Software representation of the device. Translates device actions into events other proxies can interpret (and vice versa). Device security handled here; proxy runs on a trusted computer.

Example: Information Appliance Wireless Comm. Wireless Comm. VCR Proxy Commands and status The proxy has an ACL that limits who can control the VCR.

Example: Location-aware Mobile Speaker Cricket Listener Wireless Comm. Wireless Comm. Speaker Proxy Speaker Proxy Speaker can behave differently based on its location (which is only known to its proxy). Location and audio data

Example: Badge (Key21) Device Cricket Listener Wireless Key21 The proxy has an ACL that limits who else is allowed to know the person’s location. Proxy A repository for someone’s cryptographic key Has understanding of Location Wireless communication (explained later on)

Automation Scripts Each proxy can run multiple scripts. Each script generates new events based on input events. For example: – `Matt has walked into the room’  Turn on light – `It’s 6am and it’s a workday’  Turn on the coffee machine

Layer 2: Routing/Naming Network Routing/Naming Network Proxy K21 ProxyDevice K21 ProxyDevice Proxy Farm Scripting Proxy Scripting

Proxy Scripting Play Tape Command Example: user wants to play a tape K21Proxy Name Resolution Play Tape Command Routing

Naming Distributed network of name resolvers/routers INS-style names: – [id=spk03 [loc=ne43-226] [devtype=speaker]] – [id=* [loc=ne43-226] [devtype=speaker]] – [id=* [loc=ne43-226] [devtype=*]]

Layer 3: Proxy-Based Security Naming/Routin g Network Proxy K21Proxy Device-to-Proxy Security Protocol Proxy-to-Proxy Security Protocol Device-to-Proxy Security Protocol Proxy-to-Proxy Security Protocol The two protocol architecture allows for simple devices to have a simple protocol, and complex devices to have a sophisticated protocol.

Device-Proxy Security Cricket Listener Wireless Comm. Wireless Comm. K21 K21 Proxy Secure Communication 1.Device-dependent protocol. 2.Device and Proxy share 128-bit symmetric keys. 3.Communication between device and proxy is encrypted and MAC’d. 4.Sequence numbers used for protection against replay attacks Location

Proxy-Proxy Security Proxy Scripting K21Proxy Name ResolutionRouting SPKI/SDSI Over SSL/TLS SPKI/SDSI Over SSL/TLS All proxies talk to each other with the same protocol.

Status System design completed and largely implemented. Being evaluated in terms of performance and scalability Ongoing work: Security issues with anonymous computation and/or minimally-trusted computers

Questions?