Paper 2022/569

TinyABE: Unrestricted Ciphertext-Policy Attribute-Based Encryption for Embedded Devices and Low-Quality Networks

Marloes Venema and Greg Alpár

Abstract

Ciphertext-policy attribute-based encryption (CP-ABE) has attracted much interest from the practical community to enforce access control in distributed settings such as the Internet of Things (IoT). In such settings, encryption devices are often constrained, having small memories and little computational power, and the associated networks are lossy. To optimize both the ciphertext sizes and the encryption speed is therefore paramount. In addition, the master public key needs to be small enough to fit in the encryption device's memory. At the same time, the scheme needs to be expressive enough to support common access control models. Currently, however, the state of the art incurs undesirable efficiency trade-offs. Existing schemes often have linear ciphertexts, and consequently, the ciphertexts may be too large and encryption may be too slow. In contrast, schemes with small ciphertexts have extremely large master public keys, and are generally computationally inefficient. In this work, we propose TinyABE: a novel CP-ABE scheme that is expressive and can be configured to be efficient enough for settings with embedded devices and low-quality networks. In particular, we demonstrate that our scheme can be configured such that the ciphertexts are small, encryption is fast and the master public key is small enough to fit in memory. From a theoretical standpoint, the new scheme and its security proof are non-trivial generalizations of the expressive scheme with constant-size ciphertexts by Agrawal and Chase (TCC'16, Eurocrypt'17) and its proof to the unbounded setting. By using techniques of Rouselakis and Waters (CCS'13), we remove the restrictions that the Agrawal-Chase scheme imposes on the keys and ciphertexts, making it thus more flexible. In this way, TinyABE is especially suitable for IoT.