  Attribute-Based Encryption (ABE) is an emerging cryptographic technique that
allows one to embed a fine-grained access control mechanism into encrypted
data. In this paper we propose a novel ABE scheme called SEA-BREW (Scalable and
Efficient Abe with Broadcast REvocation for Wireless networks), which is suited
for Internet of Things (IoT) and Industrial IoT (IIoT) applications. In
contrast to state-of-the-art ABE schemes, ours is capable of securely
performing key revocations with a single short broadcast message, instead of a
number of unicast messages that is linear with the number of nodes. This is
desirable for low-bitrate Wireless Sensor and Actuator Networks (WSANs) which
often are the heart of (I)IoT systems. In SEA-BREW, sensors, actuators, and
users can exchange encrypted data via a cloud server, or directly via wireless
if they belong to the same WSAN. We formally prove that our scheme is secure
also in case of an untrusted cloud server that colludes with a set of users,
under the generic bilinear group model. We show by simulations that our scheme
requires a constant computational overhead on the cloud server with respect to
the complexity of the access control policies. This is in contrast to
state-of-the-art solutions, which require instead a linear computational
overhead.
