Cited by 234Cryptographic Implementations and SecurityQuantum Computing Algorithms and ArchitectureQuantum Information and Cryptography

The DOI matches its Crossref record; 50 of the 50 references it cites were found in a registry or an index; none of the 32 sources its claims cite is checked for support yet.

Implementing Grover Oracles for Quantum Key Search on AES and LowMC

Open access
Jaques, Samuel, Naehrig, Michael, Roetteler, Martin, Virdia, Fernando·2020·Lecture Notes in Computer Science

Abstract

Grover’s search algorithm gives a quantum attack against block ciphers by searching for a key that matches a small number of plaintext-ciphertext pairs. This attack uses \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$O(\sqrt{N})$$\end{document}O(N) calls to the cipher to search a key space of size N. Previous work in the specific case of AES derived the full gate cost by analyzing quantum circuits for the cipher, but focused on minimizing the number of qubits. In contrast, we study the cost of quantum key search attacks under a depth restriction and introduce techniques that reduce the oracle depth, even if it requires more qubits. As cases in point, we design quantum circuits for the block ciphers AES and LowMC. Our circuits give a lower overall attack cost in both the gate count and depth-times-width cost models. In NIST’s post-quantum cryptography standardization process, security categories are defined based on the concrete cost of quantum key search against AES. We present new, lower cost estimates for each category, so our work has immediate implications for the security assessment of post-quantum cryptography. As part of this work, we release Q# implementations of the full Grover oracle for AES-128, -192, -256 and for the three LowMC instantiations used in Picnic, including unit tests and code to reproduce our quantum resource estimates. To the best of our knowledge, these are the first two such full implementations and automatic resource estimations.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

The paper presents Q# implementations of full Grover oracles for AES-128/192/256 and the three LowMC instances used in Picnic, optimizing for depth under NIST’s MAXDEPTH rather than qubit width. It reports lower gate and depth-times-width costs than prior AES circuits and derives new, lower NIST security-category estimates, with an 11–13 bit gate-cost reduction.

Key findings

  • The authors release Q# implementations of the full Grover oracle for AES-128, -192, -256 and for the three LowMC instantiations used in Picnic, including unit tests and code to reproduce resource estimates; they state these are the first two such full implementations and automatic resource estimations.
  • Under a depth restriction, inner parallelization and depth-optimized circuits reduce costs: for AES-128 key search without a depth limit, G-cost is 1.34·2^83 gates and DW-cost is 1.75·2^86 qubit-cycles; with MAXDEPTH = 2^40, G-cost rises to 1.07·2^117 and DW-cost to 1.76·2^120, while with MAXDEPTH = 2^64, G-cost is 1.07·2^93.
  • For NIST categories, the paper reports a consistent gate-cost reduction of 11–13 bits: e.g. category 1 (AES-128) at MAXDEPTH = 2^40 is 1.07·2^117 versus NIST’s 2^130, and at MAXDEPTH = 2^64 is 1.07·2^93 versus 2^106; category 3 at 2^40 is 1.09·2^181 versus 2^193; category 5 at 2^40 is 1.39·2^245 versus 2^258. The exception is category 1 with MAXDEPTH = 2^96, where this work gives 1.34·2^83 versus NIST’s 2^74.
  • LowMC L1 can be broken with G-cost 1.25·2^123 in depth MAXDEPTH = 2^40, while the original NIST category 1 bound requires a scheme not to be broken by an attack using less than 2^130 gates; despite LowMC’s lower T-gate count, its large CNOT count leads to higher G-cost and DW-cost than AES when all gates are counted.

Methods

  • Design: Q# circuits for AES and LowMC using Clifford+T gates, AND gates, PLU decompositions for linear maps, in-place AES key expansion, and Maximov’s MixColumn; resource estimates are obtained automatically from the Q# compiler, with unit tests against Python/PyCryptodome and the LowMC C++ reference.
  • Grover analysis: key search uses r plaintext-ciphertext pairs, with spurious-key probabilities derived under pseudo-random permutation/function heuristics; under MAXDEPTH, the paper uses inner parallelization by dividing the key space and evaluates G-cost and depth-times-width (DW-cost) metrics.
  • Data/sample: AES-128/192/256 and the three LowMC parameter sets (128, 192, 256) used in Picnic; the main analysis is resource estimation from the Q# implementations and comparison to prior work and NIST formulas.

Limitations

  • Stated: the paper ignores layout and communication costs, assumes full parallelism and free rewiring, and notes that the Q# compiler cannot optimize small circuit variations; measurement-based gate counts are probabilistic because PRNG seeding is unsupported.
  • Stated: the LowMC implementation uses the original LowMC design and is suboptimal, and the authors defer a final conclusion on relative LowMC-vs-AES security until LowMC circuits are optimized to a similar extent.
  • Evident from the text: resource estimates depend on the specific Q# compiler/QDK versions and assumptions, and the security-category implications rely on heuristic block-cipher assumptions and chosen MAXDEPTH values rather than a modeled physical fault-tolerant architecture.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1007/978-3-030-45724-2_10

Cites

50 of 50 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Figures

Fig. 1 Alternative circuits implementing the same linear transformation M : F 4 2 → F 4 2 , by using the two strategies described in § 3.3. Both are direct implementations, and could potentially be reduced in size by automatic means as in [MSR + 19], [MSC + 19], [GKMR14] and [ZC19], or manually. Figure 1b is wider and has a larger gate count, but is shallower, than Figure 1c.
Fig. 1 Alternative circuits implementing the same linear transformation M : F 4 2 → F 4 2 , by using the two strategies described in § 3.3. Both are direct implementations, and could potentially be reduced in size by automatic means as in [MSR + 19], [MSC + 19], [GKMR14] and [ZC19], or manually. Figure 1b is wider and has a larger gate count, but is shallower, than Figure 1c.From the PDF
Fig. 2 In-place AES key expansion for AES-128, AES-192, and AES-256, deriving the i th set of N k round key words from the ( i -1) th set. Each | k j 〉 i represents the j th word of | k 〉 i . SubByte takes the input state on the top wire, and returns the output on the bottom wire, while ↕ SubByte takes inputs on the bottom wire, and returns outputs on the top. Dashed lines indicate that the corresponding wire is not used in the ↕ SubByte operation. RC represents the round constant addition, which is implemented by applying X gates as appropriate.
Fig. 2 In-place AES key expansion for AES-128, AES-192, and AES-256, deriving the i th set of N k round key words from the ( i -1) th set. Each | k j 〉 i represents the j th word of | k 〉 i . SubByte takes the input state on the top wire, and returns the output on the bottom wire, while ↕ SubByte takes inputs on the bottom wire, and returns outputs on the top. Dashed lines indicate that the corresponding wire is not used in the ↕ SubByte operation. RC represents the round constant addition, which is implemented by applying X gates as appropriate.From the PDF
(b) AES-192 operation.
(b) AES-192 operation.From the PDF
(a) AES-256 operation.
(a) AES-256 operation.From the PDF
Image 5
From the PDF
Fig. 6 Grover oracle construction from AES using two message-ciphertext pairs. FwAES represents the ForwardAES operator described in § 4.6. The middle operator '=' compares the output of AES with the provided ciphertexts and flips the target qubit if they are equal.
Fig. 6 Grover oracle construction from AES using two message-ciphertext pairs. FwAES represents the ForwardAES operator described in § 4.6. The middle operator '=' compares the output of AES with the provided ciphertexts and flips the target qubit if they are equal.From the PDF
Fig. 7 AND gate design used in our circuit. We notice that in (b), the measurement returns a classical bit b and leaves the original qubit in the state | b 〉 .
Fig. 7 AND gate design used in our circuit. We notice that in (b), the measurement returns a classical bit b and leaves the original qubit in the state | b 〉 .From the PDF
Fig. 8 Dummy S-box design, that tries to forcefully avoid non-parallel calls to the S-box to be partially executed at the same time.
Fig. 8 Dummy S-box design, that tries to forcefully avoid non-parallel calls to the S-box to be partially executed at the same time.From the PDF

Verification

Claims the paper makes

34 Own interpretation · 34 No basis given · 25 Own result · 23 Sources not found · 2 Not checked yet · 2 Own method

  • It may state two separate claims as one. 44
  • The quote only partly states this claim. 1
  • Probably not a substantial claim. 19
60 of 60
  • The authors state this as an assumption.

    Under a fixed key K, the map m -> C_K(m) is a pseudo-random permutation; under a fixed message block m, the map K -> C_K(m) is a pseudo-random function.

    “We assume that under a fixed key K , the map { 0 , 1 } n →{ 0 , 1 } n , m ↦→ C K ( m ) is a pseudo-random permutation; and under a fixed message block m , the map { 0 , 1 } k → { 0 , 1 } n , K ↦→ C K ( m ) is a pseudo-random function.”
  • The authors state this as an assumption.

    Any quantum adversary is bounded by a constraint on its total depth for running a quantum circuit.

    “In this work, we assume that any quantum adversary is bounded by a constraint on its total depth for running a quantum circuit.”
  • The authors state this as an assumption.

    MAXDEPTH constitutes a hard upper bound on the total depth of a quantum attack, including possible repetitions of a Grover instance.

    “We do assume that MAXDEPTH constitutes a hard upper bound on the total depth of a quantum attack, including possible repetitions of a Grover instance.”
  • The authors state this as an assumption.

    The overall attack strategy is guaranteed to return a solution with high probability close to 1 within the given depth bound.

    “We consider it reasonable to expect that the overall attack strategy is guaranteed to return a solution with high probability close to 1 within the given depth bound.”
  • The authors state this as an assumption.

    Full parallelism holds: a quantum circuit can apply any number of gates simultaneously so long as these gates act on disjoint sets of qubits.

    “We make the standard assumption of full parallelism , meaning that a quantum circuit can apply any number of gates simultaneously so long as these gates act on disjoint sets of qubits [BBG + 13,GR03].”
  • The authors state this as an assumption.

    Layout and communication costs for the Grover oracle circuit are ignored.

    “We ignore all concerns of layout and communication costs for the Grover oracle circuit.”
  • The authors state this as an assumption.

    Parallelization of Grover's algorithm uses inner parallelization via splitting up the search space.

    “This necessarily means that we must include parallelization, which we assume to use inner parallelization via splitting up the search space, see § 2.3.”
    “Imposing a depth limit forces the parallelization of Grover's algorithm, which we assume uses inner parallelization, see § 2.3.”
7 of 7

Citations

Cites

Show all 48 references

Cited by

Sorted by citations

See all 234

Metadata

Authors
Jaques, S., Naehrig, M., Roetteler, M., & Virdia, F.
Affiliations
  • University of Oxford (GB)
  • Microsoft (United States) (US)
  • Royal Holloway University of London (GB)
Corresponding author
  • Jaques, Samuel
  • Naehrig, Michael
Venue
Lecture Notes in Computer Science
Published
2020
Pages
280-310
ISSN
  • 0302-9743 (ISSN-L)
  • 1611-3349
OpenAlex
W2979004593
Cited by
234
References
48
Citations by year
2026: 27 · 2025: 36 · 2024: 47 · 2023: 38 · 2022: 33 · 2021: 31 · 2020: 19
FWCI
11.54
Type
conference paper
Language
en
Open access
Locations
  • Lecture notes in computer science (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • arXiv (Cornell University)
Funders
  • Microsoft Research
  • Government of the United Kingdom
  • University of Oxford
  • Engineering and Physical Sciences Research Council (EP/P009301/1)
  • Royal Holloway, University of London (EP/P009301/1)
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Cryptographic Implementations and Security
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Computing Algorithms and Architecture
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Information and Cryptography
Keywords
Grover's algorithm, AES, block cipher, quantum circuit design, circuit depth, gate count, post-quantum cryptography, picnics, quantum resource estimation

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

A language model drew the claims from the paper on 2026-10-23, under version 3 of the claim definition (model deepseek-v4.1-flash, prompt extract-v3).

A second model labelled each claim on 2026-10-23 (model jev-1.13-20260917, definition revision gold-guideline-v0.2).

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

Are you an author, or do you see a problem with this page? Request a review