2 Search Results for "Broadbent, Christopher H."

Document

DOI: 10.4230/LIPIcs.ITCS.2025.7

Simultaneous Haar Indistinguishability with Applications to Unclonable Cryptography

Authors: Prabhanjan Ananth, Fatih Kaleoglu, and Henry Yuen

Published in: LIPIcs, Volume 325, 16th Innovations in Theoretical Computer Science Conference (ITCS 2025)

Abstract

We study a novel question about nonlocal quantum state discrimination: how well can non-communicating - but entangled - players distinguish between different distributions over quantum states? We call this task simultaneous state indistinguishability. Our main technical result is to show that the players cannot distinguish between each player receiving independently-chosen Haar random states versus all players receiving the same Haar random state. We show that this question has implications to unclonable cryptography, which leverages the no-cloning principle to build cryptographic primitives that are classically impossible to achieve. Understanding the feasibility of unclonable encryption, one of the key unclonable primitives, satisfying indistinguishability security in the plain model has been a major open question in the area. So far, the existing constructions of unclonable encryption are either in the quantum random oracle model or are based on new conjectures. We leverage our main result to present the first construction of unclonable encryption satisfying indistinguishability security, with quantum decryption keys, in the plain model. We also show other implications to single-decryptor encryption and leakage-resilient secret sharing. These applications present evidence that simultaneous Haar indistinguishability could be useful in quantum cryptography.

Cite as

Prabhanjan Ananth, Fatih Kaleoglu, and Henry Yuen. Simultaneous Haar Indistinguishability with Applications to Unclonable Cryptography. In 16th Innovations in Theoretical Computer Science Conference (ITCS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 325, pp. 7:1-7:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{ananth_et_al:LIPIcs.ITCS.2025.7,
  author =	{Ananth, Prabhanjan and Kaleoglu, Fatih and Yuen, Henry},
  title =	{{Simultaneous Haar Indistinguishability with Applications to Unclonable Cryptography}},
  booktitle =	{16th Innovations in Theoretical Computer Science Conference (ITCS 2025)},
  pages =	{7:1--7:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-361-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{325},
  editor =	{Meka, Raghu},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2025.7},
  URN =		{urn:nbn:de:0030-drops-226352},
  doi =		{10.4230/LIPIcs.ITCS.2025.7},
  annote =	{Keywords: Quantum, Haar, unclonable encryption}
}

Document

DOI: 10.4230/LIPIcs.STACS.2012.589

The Limits of Decidability for First Order Logic on CPDA Graphs

Authors: Christopher H. Broadbent

Published in: LIPIcs, Volume 14, 29th International Symposium on Theoretical Aspects of Computer Science (STACS 2012)

Abstract

Higher-order pushdown automata (n-PDA) are abstract machines equipped with a nested 'stack of stacks of stacks'. Collapsible pushdown automata (n-CPDA) extend these devices by adding `links' to the stack and are equi-expressive for tree generation with simply typed lambda-Y terms. Whilst the configuration graphs of HOPDA are well understood, relatively little is known about the CPDA graphs. The order-2 CPDA graphs already have undecidable MSO theories but it was only recently shown by Kartzow [Kartzow 2010] that first-order logic is decidable at the second level. In this paper we show the surprising result that first-order logic ceases to be decidable at order-3 and above. We delimit the fragments of the decision problem to which our undecidability result applies in terms of quantifer alternation and the orders of CPDA links used. Additionally we exhibit a natural sub-hierarchy enjoying limited decidability.

Cite as

Christopher H. Broadbent. The Limits of Decidability for First Order Logic on CPDA Graphs. In 29th International Symposium on Theoretical Aspects of Computer Science (STACS 2012). Leibniz International Proceedings in Informatics (LIPIcs), Volume 14, pp. 589-600, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2012)

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@InProceedings{broadbent:LIPIcs.STACS.2012.589,
  author =	{Broadbent, Christopher H.},
  title =	{{The Limits of Decidability for First Order Logic on CPDA Graphs}},
  booktitle =	{29th International Symposium on Theoretical Aspects of Computer Science (STACS 2012)},
  pages =	{589--600},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-35-4},
  ISSN =	{1868-8969},
  year =	{2012},
  volume =	{14},
  editor =	{D\"{u}rr, Christoph and Wilke, Thomas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2012.589},
  URN =		{urn:nbn:de:0030-drops-34334},
  doi =		{10.4230/LIPIcs.STACS.2012.589},
  annote =	{Keywords: Collapsible Pushdown Automata, First Order Logic, Logical Reflection}
}

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2 Search Results for "Broadbent, Christopher H."

Simultaneous Haar Indistinguishability with Applications to Unclonable Cryptography

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The Limits of Decidability for First Order Logic on CPDA Graphs

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