International Association for Cryptologic Research

International Association
for Cryptologic Research


Attribute-Based Multi-Input FE (and more) for Attribute-Weighted Sums

Shweta Agrawal , IIT Madras
Junichi Tomida , NTT Social Informatics Laboratories
Anshu Yadav , IIT Madras
DOI: 10.1007/978-3-031-38551-3_15 (login may be required)
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Presentation: Slides
Conference: CRYPTO 2023
Abstract: Recently, Abdalla, Gong and Wee (Crypto 2020) provided the first functional encryption scheme for attribute-weighted sums (AWS), where encryption takes as input $N$ (unbounded) attribute-value pairs $\Set{x_i, z_i}_{i \in [N]}$ where $x_i$ is public and $z_i$ is private, the secret key is associated with an arithmetic branching programs $f$, and decryption returns the weighted sum ${\sum}_{{i \in [N]}} f(x_i)^\top z_i$, leaking no additional information about the $z_i$'s. We extend FE for AWS to the significantly more challenging multi-party setting and provide the first construction for {\it attribute-based} multi-input FE (MIFE) supporting AWS. For $i \in [n]$, encryptor $i$ can choose an attribute $y_i$ together with AWS input $\Set{x_{i,j}, z_{i,j}}$ where $j \in [N_i]$ and $N_i$ is unbounded, the key generator can choose an access control policy $g_i$ along with its AWS function $h_i$ for each $i \in [n]$, and the decryptor can compute $$\sum_{i \in [n]} \sum_{j \in [N_{i}]}h_{i}(x_{i,j})^\top z_{i,j} \text{ iff } g_{i}(y_{i}) =0 \text{ for all } i \in [n]$$ Previously, the only known attribute based MIFE was for the inner product functionality (Abdalla \etal~Asiacrypt 2020), where additionally, $y_i$ had to be fixed during setup and must remain the same for all ciphertexts in a given slot. Our attribute based MIFE implies the notion of multi-input attribute based encryption (MIABE) recently studied by Agrawal, Yadav and Yamada (Crypto 2022) and Francati, Friolo, Malavolta and Venturi (Eurocrypt 2023), for a conjunction of predicates represented as arithmetic branching programs (ABP). Along the way, we also provide the first constructions of multi-client FE (MCFE) and dynamic decentralized FE (DDFE) for the AWS functionality. Previously, the best known MCFE and DDFE schemes were for inner products (Chotard \etal~ePrint 2018, Abdalla, Benhamouda and Gay, Asiacrypt 2019, and Chotard \etal~Crypto 2020).
  title={Attribute-Based Multi-Input FE (and more) for Attribute-Weighted Sums},
  author={Shweta Agrawal and Junichi Tomida and Anshu Yadav},