INSENS: Intrusion-Tolerant Routing For Wireless Sensor Networks

By: Jing Deng, Richard Han, Shivakant Mishra

Presented by: Daryl Lonnon

INSENS Goals

Define a secure & intrusion-tolerant routing scheme.

A small number of compromised nodes can only effect a small/localized area.

Compromised nodes cannot bring down the entire network.

INSENS: Goals

INSENS: Challenges

Wireless communication is broadcast in nature; adversaries can: Eavesdrop on packets as they cross

the network Tamper with transmitted packets Inject packets to initiate DOS

Challenges (continued) Sensor nodes are highly constrained:

Limited power/lifetime Low-power micro-sensors and actuators Slow embedded processors Limited memory Low bandwidth communication

Distributed in the field in-situ, lacking physical security.

INSENS: Underlying Framework

Large number of resource poor sensor nodes. 10-100 nodes for home monitoring 1000+ nodes for battlefield and

building monitoring Small number of resource rich

base stations.

High Level Design Principles to Achieve Intrusion Tolerance

Securely build redundant routing. Only trusted base stations may

initiate expensive network operations (such as route setup).

Symmetric key encryption performed between base stations and nodes.

High Level Principles (Continued) Base stations perform expensive

operations for nodes (i.e. route table computation).

Secure only common traffic patterns. Base station -> node/aggregator Aggregator/node -> base station

Nodes are static (motionless) after setup.

High Level Principles (Continued)

Novel mechanisms can be used to overcome specific attacks.

Allow for multiple base stations and multiple routes to those base stations.

Threat Model

Adversary can compromise a node, obtaining all information (e.g. keys, routing info), as well as, reprogram a node.

An adversary has a jamming range of d, where d is >= a nodes transmission range, and d << the radius of the complete network.

Threat Model (continued)

An adversary can only hear a node if the node can hear the adversary, the adversary may, however, transmit much further than a node.

An adversary cannot tamper with a base station (without being detected).

INSENS: Basic Protocol

Divided into two separate phases. Route Discover – determines the

topology of the network Data Forwarding – is the normal

operation of the network

INSENS: Basic Protocol Assumptions and Preconditions

Assumption: Communication between nodes is symmetric (if a can hear b, b can hear a).

Preconditions: each node possess: A symmetric key shared with the base

station, which is used to create to derived keys and

A globally known one way hash function F The initial number of a one way hash chain

eK mK

oS

INSENS: Basic Protocol Route Discovery Overview

Base station securely floods a request message.

Nodes send local topology to base station in a feedback message.

Base station sends each node a specific routing update message.

Basic INSENS: Route Request

The base station sends a route request message to each of it’s neighbors.

Each node saves the neighbor that it first received a request from and forwards a modified route request.

Route Request Messages

bsID

),( 0msgKMAC bs

0msg

Base Station

REQ

OHC

oMAC

xID

)||,( 1xxx MACmsgKMAC

xmsg

Node x

REQ

OHC

xMAC

…

Basic INSENS: Feedback Each node waits some amount of

time, listening for neighbors flooding the request message.

After some timeout, each node sends a feedback message to it’s parent.

)),(,(),( xxexxmxxex NBRKEIDFDBKOHCKMACNBRKEIDFDBKyx

nxnxnnnnx MACIDMACIDMACIDNBR ...2211

INSENS: Route Discovery

The base station waits for feedback messages, and uses those neighbor lists to build route tables.

A shortest path algorithm is used to generate the first path between a node and a base station.

INSENS: Route Discovery (Second Path)

The second path is generated first by creating three sets of nodes: N1 are nodes along the path (not

including the base station and target node).

N2 are nodes that are neighbors to node in N1.

N3 are nodes that are neighbors to nodes in N2.

INSENS: Path Formation Remove N3 from the “network”, and

compute shortest path. If a path exists, you have the second path.

Remove N2 from the “network”, and compute the shortest path. If a path exists, you have the second path.

Remove N1 from the “network”, and compute the shortest path. If a path exists you have the second path.

If all fail, you have no second path.

Data Forwarding Tables For each node in a path, add to that

nodes routing table a 3-tuple <destination,source,immediate sender>

After all paths have been calculated, unicast each node it’s table.

If a node detects a message, it searches its table and broadcasts the message if it matches an entry.

Basic INSENS Protocol1. BS floods request message

2. Nodes respond with feedback

3. BS determines shortest path

4. BS builds sets N1, N2 & N3

5. BS determines 2nd shortest path

6. BS sends out routing tables

N1

N2

N3

Limitations of Basic INSENS

Wireless communication is not always symmetric.

Feedback messages can get long. Base station can get overloaded on

large networks. No maintenance of network routing

for failed and/or new nodes.

Enhanced INSENS adds

Bidirectional verification. Secure multi-path multi-base

station routing. Maintenance issues: message loss,

nodes joining and leaving.

Bidirectional Verification Defends against Rushing attacks. Echo-back process to verify neighbor

nodes. Each node uses a temporary global key to

setup pairwise keys with it’s neighbors During the handshake for pairwise keys, it

verifies which nodes are neighbors. Each node, then, unicasts a random cluster

key to all its valid neighbors. REQ messages are broadcast encrypted

and authenticated with the cluster key.

Secure Multi-Path Multi-Base Station Routing Each node uses bi-directional verification to

determine neighbors and setup cluster keys. Each base station floods a request message:

Each node that receives the request, verifies the OHC, replaces id with it’s id and rebroadcasts the message using it’s cluster key.

This constructs multiple secure trees that span the network.

),( bCsS IDOHCKEIDREQ

Maintenance: Local Repair Local repair is used to add new nodes

and fix holes in network. If node u has not received a REQ

message after some time t, it sends an authenticated (with it’s cluster key) message (P REQ).

Nodes that have received a REQ message send an authenticated (with their pair-wise key) affirmative response.

Node u picks a node at random that gave an affirmative response.

Maintenance: Pair-Wise Key Setup with New Nodes Before deleting their global key, old

nodes save off a set of These pairs are used to query a new

node u, to determine if it has the global key.

The new node then queries an existing node by asking for it’s id and computing a key ( (using it’s polynomial share?)) and initiating a challenge response.

),(, RandKERand G

xK

Enhanced INSENS Protocol1. Nodes use global key to find

and setup pair-wise and clusterkeys with neighbors.

2. BS floods request message, which is forwarded on using cluster keys.

3. Nodes note first neighbor to send request to build minimum spanning tree.

Implementation: Basic INSENS

Motes running TinyOS 1.0 with NesC. Base station running Java. RC5 used for encryption. CBC mode of RC5 used to generate

MACs. RC5 over known plain text with result

being next key to generate hash chain.

Implementation: Basic INSENS 36 byte packet fragmentation by dropping

packets with higher sequence numbers. Network setup was dominated by timeout

at sensor nodes.

Performance (Cryptographic) of Enhanced INSENS

Cryptographic storage = 8 x (2n +k +l + 2) where key size is 8 bytes, n neighbors, l random numbers, and k base stations.

4 milliseconds to encrypt a message.

4.2 milliseconds to verify hash chain and 136 bytes overhead.

Effectiveness of Multipath Routing 2000 nodes, each node averaging

16 neighbors. Enhanced INSENS with 4 base

stations Basic INSENS with 2 paths Single path routing.

Jamming range = activity range; enhance was 3 times better, basic was 2 times better.

Effectiveness of Multi-Path Routing Jamming range = 2 x activity range;

Enhance was 2 times better, basic was about equal to single path.

Jamming range = 3 x activity range; Enhance was about 1.5 times better, basic was equal to single path.

Versus rushing attacks, echo back almost completely eliminated blocked nodes.