Paper 2024/328

Attribute-Based Signatures with Advanced Delegation, and Tracing

Abstract

Attribute-based cryptography allows fine-grained control on the use of the private key. In particular, attribute-based signature (ABS) specifies the capabilities of the signer, which can only sign messages associated to a policy that is authorized by his set of attributes. Furthermore, we can expect signature to not leak any information about the identity of the signer. ABS is a useful tool for identity-preserving authentication process which requires granular access-control, and can furthermore be enhanced with additional properties, for example delegation where users are able to manage a set of keys derived from their original one. In this paper, we address delegation of signing keys. Our first delegation works for any subset of the original attributes, which is the intuitive approach of delegation. Furthermore, we also provide another kind of delegation where the delegator can choose a policy at delegation time to produce keys that can sign any message under this specific policy. This last approach to delegation is a direct application of a new version of the indexing technique, which was first introduced by Okamoto and Takashima in order to prove adaptive security in ABS and its counterpart for encryption, ABE. On top of that, we prove that our scheme is compatible with a well studied feature of ABS, traceability, by using an approach based on Linearly-Homomorphic signatures. All our schemes also guarantee the anonymity of the real signer. The unforgeability of our schemes is proven using the SXDH assumption, and our constructions use the Dual Pairing Vector Spaces (DPVS) framework developed by Okamoto and Takashima, which has been widely used for all kind of attribute and functional cryptography mechanisms.