IEEE 802.15.4 security

The IEEE 802.15.4 standard includes security provisions in the form of encryption and authentication. The architect has flexibility in the security of the network based on cost, performance, security, and power. The different security suites are listed in the following table. 

AES-based encryption uses a block cipher with a counter mode. The AES-CBC-MAC provides authentication-only protection, and the AES-CCM mode provides the full suite of encryption and authentication. The 802.15.4 radios provide an access control list (ACL) to control which security suite and keys to use. Devices can store up to 255 ACL entries. 

The MAC layer also computes "freshness checks" between successive repetitions to ensure old frames or old data is no longer considered valid and will stop those frames from proceeding up the stack. 

Each 802.15.4 transceiver must manage its own ACL and populate it with a list of "trusted neighbors" along with the security policies. The ACL includes the address of the node cleared to communicate with, the particular security suite to use (AES-CTR, AES-CCM-xx, AES-CBC-MAC-xx), the key for the AES algorithm, and the last initial vector (IV) and replay counter. The table below lists the various 802.15.4 security modes and features.

 

Symmetric cryptography relies on both endpoints using the same key. Keys can be managed at a network level using a shared network key. This is a simple approach where all nodes possess the same key but are at risk of insider attacks. A pairwise keying scheme could be used where unique keys are shared between each pair of nodes. This mode adds overhead, especially for networks where there is a high fan out from nodes to neighbors. Group keying is another option. In this mode, a single key is shared among a set of nodes and is used for any two nodes of the group. Groups are based on device similarities, geographies, and so on. Finally, a hybrid approach is possible, combining any of the three schemes mentioned.