K21 and Automation System Architecture

Matthew Burnsideevent@mit.edu

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

LampCoffeeMaker

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

Devicecommunication Scripting

Event-Based Communication

All messages are passed in the form of events. <STATUS_CHANGE_EVENT, light_bulb=on> <COMMAND_EVENT, play_tape=true>

Layer 1: Device Communication

DeviceWireless

Transceiver

DeviceWireless

Transceiver

DeviceWireless

Transceiver

EthernetCard

WirelessTransceiver

Proxy

Proxy

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

WirelessComm.

WirelessComm. VCR ProxyVCR Proxy

Commands and status

The proxy has an ACL that limits who can control the VCR.

Example:Location-aware Mobile Speaker

Cricket Listener

Cricket Listener

WirelessComm.

WirelessComm.

SpeakerProxy

SpeakerProxy

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

Cricket Listener WirelessWireless

Key21

The proxy has an ACL that limits who else is allowed to know the person’s location.

ProxyProxy

•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

Proxy

Device K21

Proxy

Device

Proxy Farm Proxy Farm

ScriptingProxy

Scripting

ProxyScripting

Play TapeCommand

Example: user wants to play a tape

K21

Proxy

Name Resolution

Play TapeCommand

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/Routing Network

Naming/Routing Network

ProxyProxy

K21

Proxy

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

Cricket Listener

WirelessComm.

WirelessComm.

K21

K21 ProxyK21 Proxy

Secure Communication

1. Device-dependent protocol.

2. Device and Proxy share 128-bit symmetric keys.

3. Communication between device andproxy is encrypted and MAC’d.

4. Sequence numbers used for protection against replay attacks

Location

Proxy-Proxy Security

ProxyScripting

K21

Proxy

Name Resolution Routing

SPKI/SDSIOver SSL/TLS

SPKI/SDSIOver 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?