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Creative Commons Attribution 4.0 International license (CC BY 4.0)
When quoting this document, please refer to the following
DOI: 10.4230/LIPIcs.CCC.2022.23
URN: urn:nbn:de:0030-drops-165852
URL: http://dagstuhl.sunsite.rwth-aachen.de/volltexte/2022/16585/
Chen, Lijie ;
Li, Jiatu ;
Yang, Tianqi
Extremely Efficient Constructions of Hash Functions, with Applications to Hardness Magnification and PRFs
Abstract
In a recent work, Fan, Li, and Yang (STOC 2022) constructed a family of almost-universal hash functions such that each function in the family is computable by (2n + o(n))-gate circuits of fan-in 2 over the B₂ basis. Applying this family, they established the existence of pseudorandom functions computable by circuits of the same complexity, under the standard assumption that OWFs exist. However, a major disadvantage of the hash family construction by Fan, Li, and Yang (STOC 2022) is that it requires a seed length of poly(n), which limits its potential applications.
We address this issue by giving an improved construction of almost-universal hash functions with seed length polylog(n), such that each function in the family is computable with POLYLOGTIME-uniform (2n + o(n))-gate circuits. Our new construction has the following applications in both complexity theory and cryptography.
- (Hardness magnification). Let α : ℕ → ℕ be any function such that α(n) ≤ log n / log log n. We show that if there is an n^{α(n)}-sparse NP language that does not have probabilistic circuits of 2n + O(n/log log n) gates, then we have (1) NTIME[2ⁿ] ⊈ SIZE[2^{n^{1/5}}] and (2) NP ⊈ SIZE[n^k] for every constant k. Complementing this magnification phenomenon, we present an O(n)-sparse language in P which requires probabilistic circuits of size at least 2n - 2. This is the first result in hardness magnification showing that even a sub-linear additive improvement on known circuit size lower bounds would imply NEXP ⊄ P_{/poly}.
Following Chen, Jin, and Williams (STOC 2020), we also establish a sharp threshold for explicit obstructions: we give an explict obstruction against (2n-2)-size circuits, and prove that a sub-linear additive improvement on the circuit size would imply (1) DTIME[2ⁿ] ⊈ SIZE[2^{n^{1/5}}] and (2) P ⊈ SIZE[n^k] for every constant k.
- (Extremely efficient construction of pseudorandom functions). Assuming that one of integer factoring, decisional Diffie-Hellman, or ring learning-with-errors is sub-exponentially hard, we show the existence of pseudorandom functions computable by POLYLOGTIME-uniform AC⁰[2] circuits with 2n + o(n) wires, with key length polylog(n). We also show that PRFs computable by POLYLOGTIME-uniform B₂ circuits of 2n + o(n) gates follows from the existence of sub-exponentially secure one-way functions.
BibTeX - Entry
@InProceedings{chen_et_al:LIPIcs.CCC.2022.23,
author = {Chen, Lijie and Li, Jiatu and Yang, Tianqi},
title = {{Extremely Efficient Constructions of Hash Functions, with Applications to Hardness Magnification and PRFs}},
booktitle = {37th Computational Complexity Conference (CCC 2022)},
pages = {23:1--23:37},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-241-9},
ISSN = {1868-8969},
year = {2022},
volume = {234},
editor = {Lovett, Shachar},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/opus/volltexte/2022/16585},
URN = {urn:nbn:de:0030-drops-165852},
doi = {10.4230/LIPIcs.CCC.2022.23},
annote = {Keywords: Almost universal hash functions, hardness magnification, pseudorandom functions}
}
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Keywords: |
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Almost universal hash functions, hardness magnification, pseudorandom functions |
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Collection: |
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37th Computational Complexity Conference (CCC 2022) |
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Issue Date: |
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2022 |
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Date of publication: |
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11.07.2022 |
