Designing attribute-based systems supporting highly expressive access policies has been
one of the principal focus of research in attribute-based cryptography. While attribute-based encryption
(ABE) enables fine-grained access control over encrypted data in a multi-user environment,
attribute-based signature (ABS) provides a powerful tool for preserving signer anonymity. Attributebased
signcryption (ABSC), on the other hand, is a combination of ABE and ABS into a unified
cost-effective primitive. In this paper, we start by presenting a key-policy ABE supporting general
polynomial-size circuit realizable decryption policies and featuring compactness. More specifically,
our ABE construction exhibits short ciphertexts and shorter decryption keys compared to existing
similar works. We then proceed to design a key-policy ABSC scheme which enjoys several interesting
properties that were never achievable before. It supports arbitrary polynomial-size circuits, thereby
handles highly sophisticated control over signing and decryption rights. Besides, it generates short
ciphertext as well. Our ABE construction employs multilinear map of level $n + l + 1$, while that
used for our ABSC scheme has level $n + n' + l + 1$, where $n$, $n'$, and $l$ represent respectively the
input length of decryption policy circuits, input size of signing policy circuits, and depth of both
kinds of circuits. Selective security of our constructions are proven in the standard model under the
Multilinear Decisional Diffie-Hellman and Multilinear Computational Diffie-Hellman assumptions
which are standard complexity assumptions in the multilinear map setting. Our key-policy constructions
can be converted to the corresponding ciphertext-policy variants achieving short ciphertext by
utilizing the technique of universal circuits.
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