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Junqing Gong

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4 papers

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TCS Journal 2024 Journal Article

Fine-grained polynomial functional encryption

Ziqi Zhu
Junqing Gong
Yuyu Wang
Haifeng Qian

In this work, we present fine-grained secure polynomial functional encryption (PFE) for degree d ≥ 1 over a field F: a ciphertext encrypts x ∈ F n, a key is associated with a degree-d polynomial P and decryption recovers P ( x ) ∈ F. Fine-grained cryptographic primitives are secure against a resources bounded class of adversaries and computed by honest users with less resources than adversaries. In this paper, we construct the fine-grained PFE in these two fine-grained settings: (1) NC 1 PFE: Based on the worst-case assumption NC 1 ⊊ ⊕ L / poly, we construct public-key polynomial functional encryption and achieve (i) selective simulation-based security and (ii) static function-hiding against adversary in NC 1 where all honest algorithms are computable in AC 0 [ 2 ] and ciphertext sizes are O ( n ). (2) AC 0 PFE: We construct a private-key polynomial functional encryption achieve unconditionally selective simulation-based security against adversary in AC 0 where all honest algorithms are computable in AC 0 and ciphertext sizes are O ( n ).

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TCS Journal 2024 Journal Article

Improved unbounded inner-product functional encryption

Minghao Yang
Junqing Gong
Haifeng Qian

In this paper, we propose an unbounded inner-product functional encryption (unbounded IPFE) scheme with semi-adaptive simulation-based security. Compared with the previous semi-adaptive secure scheme proposed by Tomida and Takashima [Asiacrypt18], our scheme enjoys about 28% shorter ciphertext and about 43% shorter secret key. Technically, we start with a bounded separable one-key IPFE scheme. In the separable one-key IPFE scheme, the public key and ciphertext can be divided into some vectors. At the same time, we develop a new transformation from a bounded separable one-key IPFE scheme towards an unbounded IPFE scheme. Finally, we give a concrete instantiation with the bounded separable one-key IPFE scheme and the transformation.

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TCS Journal 2024 Journal Article

Updatable searchable symmetric encryption: Definitions and constructions

Xiwen Wang
Kai Zhang
Junqing Gong
Shi-Feng Sun
Jianting Ning

Searchable symmetric encryption (SSE) allows a client to search over encrypted data. To address the real threat of key compromise in practice, this work initiates the study of key rotation for SSE and introduces the notion of updatable SSE (USSE). In USSE, a client can issue a single update token that permits the server to convert existing encrypted data from the old key to the new key. In particular, • we formalize the syntax of USSE and define the security model that captures the inference of key, search token, update token and encrypted data with bi-/uni-/no-directional key updates and bi-/uni-directional encrypted data updates. • we present a USSE scheme that supports conjunctive queries with sub-linear complexity, and prove its security with no-directional key update and bi-directional encrypted data update. We also give extensions for concerning different key/encrypted data updates. • we implement our USSE schemes and evaluate the performance with real-world dataset, which illustrates that our schemes achieve practically acceptable computational overhead and communication cost. Technically, our formalization of USSE is inspired by updatable encryption (UE); our USSE schemes are obtained by a semi-generic transformation from Cash et al. 's SSE and UE. The transformation itself only relies on DL and DBDH assumptions. We believe that the transformation is of independent interest and applicable to other scenarios where the SSE systems follow the structure of Cash et al. 's work.

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TCS Journal 2023 Journal Article

Bounded-collusion decentralized ABE with sublinear parameters

Jun Zhao
Minghao Yang
Junqing Gong
Kai Zhang
Haifeng Qian

In this paper, we propose a decentralized ABE scheme against bounded collusion which means the number of users in the system is a-prior bounded. The scheme enjoys public key and ciphertext of sublinear sizes in the number of users in the system while all prior constructions require linear sizes. Besides, our scheme achieves semi-adaptive security under bilateral k-Lin assumption and SXDH assumption in a pairing group. Keep the same as the previous constructions, the scheme supports monotone span program as a policy and does not rely on the random oracle. Technically, we follow Wang et al. 's “linear secret sharing scheme (LSSS) + inner-product functional encryption (IPFE)” paradigm [PKC'19] and use (an extended variant of) functional encryption for quadratic functions (QFE) in the place of IPFE. By this, we encrypt with sublinear-size random coins and later expand them to linear-size entropy for security proof. Roughly, the use of QFE requires bilateral k-Lin assumption while the entropy expansion relies on SXDH.

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