We address three practical problems of Attribute-Based Encryption (ABE) in this paper: performance, accountabil-ity and privacy. To do so, we present a novel Ciphertext-Policy Attribute-Based Encryption (CP-ABE) approach, which combines white-box accountability, hidden policies and outsourced decryption. In contrast to existing schemes, the proposed construction is not only more flexible, but also efficient enough to be used in more resource-constrained environments. This is because our construction is designed around efficient Type III bilinear maps and relies on a dedicated proxy to perform computationally ex-pensive operations. Furthermore, we provide an implementation of the proposed design. The conducted evaluation demonstrates the practicality of the approach under realistic assumptions.

Blockchains are append-only data structures, meaning their size increases steadily. As of March 2021, new nodes connecting to the Bitcoin blockchain already need to synchronize and validate more than 330 GB of data. Already now, this is an issue for resource-constrained thin clients who lack the required download, storage, or computing capacities to achieve this. In future, this issue will become even more relevant when blockchain technology is applied to new domains like the Internet of Things (IoT). We propose a new blockchain architecture that addresses this issue. Our proposal relies on incremental snapshot blocks that allow new and occasionally used clients to synchronize with the current state of the blockchain efficiently. The snapshot blocks form a second linked blockchain and are secured by the blockchain consensus algorithm. In this paper, we describe the proposed architecture in detail and evaluate its storage-saving potential using the Bitcoin blockchain. The evaluations performed show that our design can reduce the volume of data that needs to be downloaded and stored by up to 98%, thus facilitating secure blockchain-based applications also on resource-constrained thin clients like smartphones, netbooks, or IoT devices.

We present a novel Ciphertext-Policy Attribute-Based Encryption (CP-ABE) scheme, which bridges the gap between highly dynamic (industrial) environments and resource-constrained devices. Our construction combines outsourced-decryption, hidden policies and revocation to cope with the requirements posed by such environments. In contrast to existing schemes, which typically rely on composite order bilinear groups, we present a scheme in prime order groups. The resulting scheme is more efficient as it relies on smaller group orders. We prove our scheme is secure under the Symmetric External Diffie-Hellman (SXDH) assumption. Lastly, we compare our scheme against existing schemes and provide timing results of our software implementation. Our evaluation shows that the proposed scheme is flexible enough for the targeted environment while improving performance by an order of magnitude.