Efficient Fuzzy Private Set Intersection from Secret-shared OPRF
Pith reviewed 2026-05-10 11:07 UTC · model grok-4.3
The pith
Fuzzy private set intersection for Lp distances achieves linear complexity using an oblivious programmable PRF with secret-shared outputs and a logarithmic prefix technique.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We propose efficient FPSI protocols for Lp distance metrics primarily leveraging significantly cheaper symmetric-key operations. Our protocols achieve linear communication and computation complexity in the set sizes m,n, the dimension d, and the distance threshold δ. Our core building block is an oblivious programmable PRF with secret-shared outputs, which may be of independent interest. Furthermore, we incorporate a prefix technique that reduces the dependence on the distance threshold δ to logarithmic, which is particularly suitable for large δ. We implement our FPSI protocols and compare them with state-of-the-art constructions, demonstrating speedups of 12~145× in running time and a 3~8×
What carries the argument
An oblivious programmable PRF with secret-shared outputs, which lets one party program the function obliviously while both parties receive additive shares of the PRF values so that only matching elements under the distance threshold can be identified without extra leakage.
Load-bearing premise
The oblivious programmable PRF with secret-shared outputs can be built efficiently and proven secure under standard assumptions, and the prefix technique does not introduce new leakage.
What would settle it
A re-implementation of the protocols on the same benchmarks that fails to show at least a 9× speedup in running time or a 3× reduction in communication compared to the cited prior works would falsify the efficiency claims.
Figures
read the original abstract
Private set intersection (PSI) enables a sender holding a set $Q$ of size $m$ and a receiver holding a set $W$ of size $n$ to securely compute the intersection $Q \cap W$. Fuzzy PSI (FPSI) is a PSI variant where the receiver learns the items $q \in Q$ for which there exists some $w \in W$ satisfying $\mathsf{dist}(q, w) \le \delta$ under a given distance metric. Although several FPSI works are proposed for $L_{p}$ distance metrics with $p \in [1, \infty]$, they either heavily rely on expensive homomorphic encryptions, or incur undesirable complexity, e.g., exponential to the element dimension, both of which lead to poor practical efficiency. In this work, we propose efficient FPSI protocols for $L_{p \in [1, \infty]}$ distance metrics, primarily leveraging significantly cheaper symmetric-key operations. Our protocols achieve linear communication and computation complexity in the set sizes $m,n$, the dimension $d$, and the distance threshold $\delta$. Our core building block is an oblivious programmable PRF with secret-shared outputs, which may be of independent interest. Furthermore, we incorporate a prefix technique that reduces the dependence on the distance threshold $\delta$ to logarithmic, which is particularly suitable for large $\delta$. We implement our FPSI protocols and compare them with state-of-the-art constructions. Experimental results demonstrate that our protocols consistently and significantly outperform existing works across all settings. Specifically, our protocols achieve a speedup of $12{\sim}145\times$ in running time and a reduction of $3{\sim}8\times$ in communication cost compared to Gao et al.~(ASIACRYPT'24) and a speedup of $9{\sim}80\times$ in running time and a reduction of $5{\sim}19\times$ in communication cost compared to Dang et al.~(CCS'25).
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes efficient fuzzy private set intersection (FPSI) protocols for L_p distance metrics (p ∈ [1, ∞]) that achieve linear communication and computation complexity in the set sizes m, n, dimension d, and logarithmic dependence on the distance threshold δ. The core innovation is an oblivious programmable PRF with secret-shared outputs, augmented by a prefix technique; the protocols rely primarily on symmetric-key operations rather than homomorphic encryption. Implementation results claim speedups of 12–145× and communication reductions of 3–8× versus Gao et al. (ASIACRYPT’24), and 9–80× speedups with 5–19× communication savings versus Dang et al. (CCS’25).
Significance. If the security reductions for the new OPRF primitive and prefix technique hold under standard assumptions, the work would constitute a meaningful practical advance in FPSI by replacing expensive public-key operations with cheaper symmetric primitives while retaining linear scaling. The experimental comparisons supply concrete evidence of improvement and the new primitive may have independent utility; these are clear strengths.
major comments (2)
- [§4] §4 (OPRF construction): the security definition and reduction for the oblivious programmable PRF with secret-shared outputs must explicitly show that sharing the outputs introduces no additional leakage beyond the intended functionality and preserves both obliviousness and programmability; this is load-bearing for the end-to-end FPSI security claim.
- [§5.2] §5.2 (prefix technique): the argument that the prefix method reduces δ dependence to O(log δ) while preserving security for arbitrary L_p metrics must rule out hidden exponential factors or p-specific failures; the current sketch leaves open whether the reduction is metric-independent.
minor comments (2)
- [Table 1] Table 1 and experimental setup: clarify the exact parameter ranges (m, n, d, δ, p) over which the 12–145× and 9–80× speedups were measured, and whether they include all overheads such as setup.
- [§2] Notation: the distinction between the receiver’s set W and the sender’s set Q is clear in the abstract but should be restated at the start of the protocol description for readability.
Simulated Author's Rebuttal
We thank the referee for the careful and constructive review. The two major comments identify areas where the security arguments can be strengthened with additional detail. We will incorporate expanded proofs and lemmas in the revised manuscript to address both points explicitly.
read point-by-point responses
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Referee: [§4] §4 (OPRF construction): the security definition and reduction for the oblivious programmable PRF with secret-shared outputs must explicitly show that sharing the outputs introduces no additional leakage beyond the intended functionality and preserves both obliviousness and programmability; this is load-bearing for the end-to-end FPSI security claim.
Authors: We agree that greater explicitness is warranted. In the revised manuscript we will augment Section 4 with a formal security definition for the secret-shared OPRF that models output sharing via additive secret sharing over a finite field. We will prove via a sequence of hybrids that the sharing introduces no leakage beyond the ideal functionality: each share is uniformly random and independent of the input given the output, so the receiver’s view is simulatable. The reduction will establish that both obliviousness (the receiver learns nothing about unprogrammed points) and programmability (the sender can set function values without revealing the key) are preserved, reducing directly to the security of the underlying OPRF under standard assumptions (random-oracle or PRF security). This will be stated as a standalone theorem before the FPSI composition. revision: yes
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Referee: [§5.2] §5.2 (prefix technique): the argument that the prefix method reduces δ dependence to O(log δ) while preserving security for arbitrary L_p metrics must rule out hidden exponential factors or p-specific failures; the current sketch leaves open whether the reduction is metric-independent.
Authors: We thank the referee for highlighting the need for a tighter argument. The prefix technique is applied to the binary representation of the computed distance value and is therefore independent of the concrete L_p metric; the metric only affects the black-box distance oracle. In the revision we will add a formal lemma in Section 5.2 showing that the technique incurs exactly O(log δ) OPRF invocations with no hidden exponential factors in δ or d. The security reduction will be metric-agnostic: the simulator uses the ideal FPSI functionality to answer prefix queries, and the view is indistinguishable regardless of p because only the comparison outcome (distance ≤ δ) is revealed. We will explicitly rule out p-specific failures by noting that the reduction never relies on properties unique to any particular p. revision: yes
Circularity Check
No significant circularity; construction builds on standard primitives with independent security claims.
full rationale
The paper introduces an oblivious programmable PRF with secret-shared outputs as a core building block (positioned as potentially of independent interest) and a prefix technique for logarithmic dependence on δ. These are presented as new constructions under standard assumptions, with linear complexity claims and empirical speedups derived from implementation comparisons rather than by definition or self-citation reduction. No equations or steps reduce the target results to fitted inputs or prior self-citations by construction. The derivation chain remains self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
axioms (1)
- standard math The security of the underlying OPRF and secret sharing primitives holds under standard assumptions.
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Figure 17: Functionality of MUX
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Ifp= 1: •List p :={(ID wi ∥k∥σ∥w σ,i,k,h,0∥|w ∗ − wi,k|)}i∈[n],k∈[d],σ∈[0,1],h∈[µ], where w∗ :=UpBound(w σ,i,k,h)ifσ= 0and w∗ :=LowBound(w σ,i,k,h)otherwise
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Ifp= 2: •Forh∈[µ],Sparsess S h =s S h,1∥sS h,2 ∈F 2 andR parsess R h =s R h,1∥sR h,2 ∈F 2. •Forh∈[µ], i∈[1, p],SandRinvokeF Mult where Sinputse h andRinputss R h,1.Sreceivesm S h and Rreceivesm R h . •Forh∈[µ],Scomputesd S h :=e 2 h + 2eh ·s S h,1 + 2mS h +s S h,2 andd R h := 2mR h +s R h,2. 5)Soutputs{d S h }h∈[µ] andRoutputs{d R h }h∈[µ]. Figure 20: Pro...
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Forj∈[m], k∈[d],Scomputes{q j,k,h}h∈[µ] := AllPrefix(qj,k, µ). 4)SandRinvoke functionalityF so-OPPRF, whereRinputsList p andSinputs {IDqj ∥k∥σ∥q j,k,h}σ∈[0,1],j∈[m],k∈[d],h∈[µ] .Sreceives {eS σ,j,k,h∥vS σ,j,k,h}σ∈[0,1],j∈[m],k∈[d],h∈[µ] andR receives{e R σ,j,k,h∥vR σ,j,k,h}σ∈[0,1],j∈[m],k∈[d],h∈[µ]
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Forσ∈[0,1], j∈[m], k∈[d], h∈[µ],SandR invoke functionalityF B2A, whereSinputsv S σ,j,k,h and Rinputsv R σ,j,k,h.Sreceivess S σ,j,k,h andRreceives sR σ,j,k,h
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Forσ∈[0,1], j∈[m], k∈[d],SandRinvoke ΠgetDistancep, whereSinputs({s S σ,j,k,h}h∈[µ], qj,k, σ), Rinputs{s R σ,j,k,h}h∈[µ].Sreceives{d S σ,j,k,h}h∈[µ] and Rreceives{d R σ,j,k,h}h∈[µ]
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Forj∈[m], k∈[d],SandRinvokeF EQSel, where Sinputs{e S σ,j,k,h, dS σ,j,k,h}σ∈[0,1],h∈[µ] andRinputs {eR σ,j,k,h, dR σ,j,k,h}σ∈[0,1],h∈[µ].Sreceivesr S j,k andR receivesr R j,k
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Forj∈[m],Scomputesr S j := P k∈[d]rS j,k, andR computesr R j :=P k∈[d]rR j,k
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Forj∈[m],SandRinvoke functionalityF Interval, whereSinputsr S j andRinputsr R j .Rreceivesb j := 1(rS j +r R j ≤δ p)
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Forj∈[m],RandSinvoke functionalityF OT, where Rinputsb j andSinputs(⊥, q j).Rreceives OT outputs zj. 11)RoutputsZ:={z j |b j = 1forj∈[m]}. Figure 21: Protocol of fuzzy PSI with prefix optimization forL p distance. |t|p fort∈[−δ, δ], i∈[n], k∈[d].Sim R appends ({rR j,k}j∈[m],k∈[d] ,O F )to the view. 3)Sim R randomly samples{d R j,k}j∈[m],k∈[d] and appends ...
work page 1901
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The paper provides a valuable step forward in the estab- lished field of Fuzzy-PSI. It significantly improves the performance of a known construction by contributing a new primitive - an OPPRF with secret shared outputs - which may be of independent interest
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