Welcome to the resource topic for 2022/215
Title:
Multi-Client Functional Encryption with Fine-Grained Access Control
Authors: Ky Nguyen, Duong Hieu Phan, David Pointcheval
Abstract:Multi-Client Functional Encryption (\mathsf{MCFE}) has been considered as an important primitive for making functional encryption useful in practice. It covers the ability to compute joint function over data from multiple parties similar to Multi-Input Functional Encryption (\mathsf{MIFE}) but it handles information leakage better than \mathsf{MIFE}. Both the \mathsf{MCFE} and \mathsf{MIFE} primitives are aimed at applications in multi-user settings where decryption can be correctly output for legitimate users only. In such a setting, the problem of dealing with access control in a fine-grained manner is particularly relevant. In this paper, we introduce a framework for \mathsf{MCFE} with fine-grained access control and propose constructions for both single-client and multi-client settings, with selective and adaptive security. The only known work that combines functional encryption in multi-user setting with access control was proposed by Abdalla \mathit{et al.} (Asiacrypt '20), which relies on a generic transformation from the single-client schemes to obtain \mathsf{MIFE} schemes that suffer a quadratic factor of n (where n denotes the number of clients) in the ciphertext size. We present a {duplicate-and-compress} technique to transform the single-client scheme and obtain a \mathsf{MCFE} with fine-grained access control scheme with only a linear factor of n in the ciphertext size. Our final scheme thus outperforms the Abdalla \mathit{et al.}'s scheme by a factor n, while \mathsf{MCFE} is more difficult to achieve than \mathsf{MIFE} (one can obtain \mathsf{MIFE} from \mathsf{MCFE} by making all the labels in \mathsf{MCFE} a fixed public constant).
ePrint: https://eprint.iacr.org/2022/215
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