TinySec: A Link Layer Security Architecture for Wireless Sensor Networks

Given the resource constraints of a typical sensor network, the temptation to forego network security must be considerable. Yet wireless networks are particularly vulnerable to network attacks. TinySec attempts to build a link layer security protocol that is, on the one hand, light-weight and easy to use enough that it will actually be deployed, and on the other hand, actually secure (cf 802.11 WEP).

Because the energy cost of transmission is high, TinySec can't afford the packet overheads of typical link layer security protocols like IPsec or TLS. But by observing that the practical bandwidth of a sensor network is relatively low, TinySec can make strong security guarantees with smaller-than-usual signatures. Also, since the transmission cost drowns out the CPU cost of encryption, TinySec can afford to use standard encryption protocols.

TinySec has been integrated into TinyOS and is fairly easy to deploy. Empirical testing reveals that the cost of security is exactly the ratio of TinySec packet size to TinyOS packet size (1 byte overhead for authenticated packets, 5 bytes for encrypted, due to the IV).

Class discussion

• TinySec seems to do a good job with link layer security, but on its own it may not be enough for real security. Key distribution is important for mitigating the damage of compromised nodes, and a challenging problem in its own right.
• The two priority scheduler introduced to reduce latency on cryptographic tasks seems a little hackish, and may have unintended effects on other tasks.

Interesting links

• Designing an Authentication System: a Dialogue in Four Scenes
• (In)Security of the WEP algorithm
• Bruce Schneier's Crypto-Gram newsletter