The Round Complexity of Black-Box Post-Quantum Secure Computation
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| Format: | Preprint |
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2025
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| _version_ | 1866909502225252352 |
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| author | Chatterjee, Rohit Liang, Xiao Pandey, Omkant Yamakawa, Takashi |
| author_facet | Chatterjee, Rohit Liang, Xiao Pandey, Omkant Yamakawa, Takashi |
| contents | We study the round complexity of secure multi-party computation (MPC) in the post-quantum regime. Our focus is on the fully black-box setting, where both the construction and security reduction are black-box. Chia, Chung, Liu, and Yamakawa [FOCS'22] demonstrated the infeasibility of achieving standard simulation-based security within constant rounds unless $\mathbf{NP} \subseteq \mathbf{BQP}$. This leaves crucial feasibility questions unresolved. Specifically, it remains unknown whether black-box constructions are achievable within polynomial rounds; also, the existence of constant-round constructions with respect to $ε$-simulation, a relaxed yet useful alternative to standard simulation, remains unestablished.
This work provides positive answers. We introduce the first black-box construction for PQ-MPC in polynomial rounds, from the minimal assumption of post-quantum semi-honest oblivious transfers. In the two-party scenario, our construction requires only $ω(1)$ rounds. These results have already been applied in the oracle separation between classical-communication quantum MPC and $\mathbf{P} = \mathbf{NP}$ in Kretschmer, Qian, and Tal [STOC'25].
As for $ε$-simulation, Chia, Chung, Liang, and Yamakawa [CRYPTO'22] resolved the issue for the two-party setting, leaving the multi-party case open. We complete the picture by presenting the first black-box, constant-round construction in the multi-party setting, instantiable using various standard post-quantum primitives.
En route, we obtain a black-box, constant-round post-quantum commitment achieving a weaker version of 1-many non-malleability, from post-quantum one-way functions. Besides its role in our MPC construction, this commitment also reduces the assumption used in the quantum parallel repetition lower bound by Bostanci, Qian, Spooner, and Yuen [STOC'24]. We anticipate further applications in the future. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2502_13830 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The Round Complexity of Black-Box Post-Quantum Secure Computation Chatterjee, Rohit Liang, Xiao Pandey, Omkant Yamakawa, Takashi Quantum Physics Cryptography and Security We study the round complexity of secure multi-party computation (MPC) in the post-quantum regime. Our focus is on the fully black-box setting, where both the construction and security reduction are black-box. Chia, Chung, Liu, and Yamakawa [FOCS'22] demonstrated the infeasibility of achieving standard simulation-based security within constant rounds unless $\mathbf{NP} \subseteq \mathbf{BQP}$. This leaves crucial feasibility questions unresolved. Specifically, it remains unknown whether black-box constructions are achievable within polynomial rounds; also, the existence of constant-round constructions with respect to $ε$-simulation, a relaxed yet useful alternative to standard simulation, remains unestablished. This work provides positive answers. We introduce the first black-box construction for PQ-MPC in polynomial rounds, from the minimal assumption of post-quantum semi-honest oblivious transfers. In the two-party scenario, our construction requires only $ω(1)$ rounds. These results have already been applied in the oracle separation between classical-communication quantum MPC and $\mathbf{P} = \mathbf{NP}$ in Kretschmer, Qian, and Tal [STOC'25]. As for $ε$-simulation, Chia, Chung, Liang, and Yamakawa [CRYPTO'22] resolved the issue for the two-party setting, leaving the multi-party case open. We complete the picture by presenting the first black-box, constant-round construction in the multi-party setting, instantiable using various standard post-quantum primitives. En route, we obtain a black-box, constant-round post-quantum commitment achieving a weaker version of 1-many non-malleability, from post-quantum one-way functions. Besides its role in our MPC construction, this commitment also reduces the assumption used in the quantum parallel repetition lower bound by Bostanci, Qian, Spooner, and Yuen [STOC'24]. We anticipate further applications in the future. |
| title | The Round Complexity of Black-Box Post-Quantum Secure Computation |
| topic | Quantum Physics Cryptography and Security |
| url | https://arxiv.org/abs/2502.13830 |