Ernest Y.-Z. Tan
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View article: Incorporating device characterization into security proofs
Incorporating device characterization into security proofs Open
Typical security proofs for quantum key distribution (QKD) rely on having some model for the devices, with the security guarantees implicitly relying on the values of various parameters of the model, such as dark count rates or detector ef…
View article: Analytic Rényi Entropy Bounds for Device-Independent Cryptography
Analytic Rényi Entropy Bounds for Device-Independent Cryptography Open
Device-independent (DI) cryptography represents the highest level of security, enabling cryptographic primitives to be executed safely on uncharacterized devices. Moreover, with successful proof-of-concept demonstrations in randomness expa…
View article: Finite-Size Analysis of Prepare-and-Measure and Decoy-State Quantum Key Distribution via Entropy Accumulation
Finite-Size Analysis of Prepare-and-Measure and Decoy-State Quantum Key Distribution via Entropy Accumulation Open
An important goal in quantum key distribution (QKD) is the task of providing a finite-size security proof without the assumption of collective attacks. For prepare-and-measure QKD, one approach for obtaining such proofs is the generalized …
View article: Finite-Size Analysis of Prepare-and-Measure and Decoy-State Quantum Key Distribution via Entropy Accumulation
Finite-Size Analysis of Prepare-and-Measure and Decoy-State Quantum Key Distribution via Entropy Accumulation Open
An important goal in quantum key distribution (QKD) is the task of providing a finite-size security proof without the assumption of collective attacks. For prepare-and-measure QKD, one approach for obtaining such proofs is the generalized …
View article: QKD security proofs for decoy-state BB84: protocol variations, proof techniques, gaps and limitations
QKD security proofs for decoy-state BB84: protocol variations, proof techniques, gaps and limitations Open
We review the current status of security proofs for practical decoy-state Quantum Key Distribution using the BB84 protocol, focusing on optical implementations with weak coherent pulses and threshold photodetectors. The primary aim of this…
View article: Marginal-constrained entropy accumulation theorem
Marginal-constrained entropy accumulation theorem Open
We derive a novel chain rule for a family of channel conditional entropies, covering von Neumann and sandwiched Rényi entropies. In the process, we show that these channel conditional entropies are equal to their regularized version, and m…
View article: Device-independent uncloneable encryption
Device-independent uncloneable encryption Open
Uncloneable encryption, first introduced by Broadbent and Lord (TQC 2020) is a quantum encryption scheme in which a quantum ciphertext cannot be distributed between two non-communicating parties such that, given access to the decryption ke…
View article: Postselection Technique for Optical Quantum Key Distribution with Improved de Finetti Reductions
Postselection Technique for Optical Quantum Key Distribution with Improved de Finetti Reductions Open
The postselection technique is an important proof technique for proving the security of quantum key distribution protocols against coherent attacks via the uplift of any security proof against independent identically distributed collective…
View article: Bounds on Petz-Rényi Divergences and their Applications for Device-Independent Cryptography
Bounds on Petz-Rényi Divergences and their Applications for Device-Independent Cryptography Open
Variational techniques have been recently developed to find tighter bounds on the von Neumann entropy in a completely device-independent (DI) setting. This, in turn, has led to significantly improved key rates of DI protocols, in both the …
View article: Mutual information chain rules for security proofs robust against device imperfections
Mutual information chain rules for security proofs robust against device imperfections Open
In this work we derive a number of chain rules for mutual information quantities, suitable for analyzing quantum cryptography with imperfect devices that leak additional information to an adversary. First, we derive a chain rule between sm…
View article: Generalized Rényi entropy accumulation theorem and generalized quantum probability estimation
Generalized Rényi entropy accumulation theorem and generalized quantum probability estimation Open
The entropy accumulation theorem, and its subsequent generalized version, is a powerful tool in the security analysis of many device-dependent and device-independent cryptography protocols. However, it has the drawback that the finite-size…
View article: Security proof for variable-length quantum key distribution
Security proof for variable-length quantum key distribution Open
We present a security proof for variable-length QKD in the Renner framework against IID collective attacks. Our proof can be lifted to coherent attacks using the postselection technique. Our first main result is a theorem to convert a sequ…
View article: Entropy bounds for device-independent quantum key distribution with local Bell test
Entropy bounds for device-independent quantum key distribution with local Bell test Open
One of the main challenges in device-independent quantum key distribution (DIQKD) is achieving the required Bell violation over long distances, as the channel losses result in low overall detection efficiencies. Recent works have explored …
View article: Postselection technique for optical Quantum Key Distribution with improved de Finetti reductions
Postselection technique for optical Quantum Key Distribution with improved de Finetti reductions Open
The postselection technique is an important proof technique for proving the security of quantum key distribution protocols against coherent attacks. In this work, we go through multiple steps to rigorously apply the postselection technique…
View article: Security Proof for Variable-Length Quantum Key Distribution
Security Proof for Variable-Length Quantum Key Distribution Open
We present a security proof for variable-length QKD in the Renner framework against IID collective attacks. Our proof can be lifted to coherent attacks using the postselection technique. Our first main result is a theorem to convert a seri…
View article: De Finetti Theorems for Quantum Conditional Probability Distributions with Symmetry
De Finetti Theorems for Quantum Conditional Probability Distributions with Symmetry Open
The aim of device-independent quantum key distribution (DIQKD) is to study protocols that allow the generation of a secret shared key between two parties under minimal assumptions on the devices that produce the key. These devices are mere…
View article: Memory effects in device-dependent and device-independent cryptography
Memory effects in device-dependent and device-independent cryptography Open
In device-independent cryptography, it is known that reuse of devices across multiple protocol instances can introduce a vulnerability against memory attacks. This is an introductory note to highlight that even if we restrict ourselves to …
View article: Composably secure device-independent encryption with certified deletion
Composably secure device-independent encryption with certified deletion Open
We study the task of encryption with certified deletion (ECD) introduced by Broadbent and Islam (2020), but in a device-independent setting: we show that it is possible to achieve this task even when the honest parties do not trust their q…
View article: Security of device-independent quantum key distribution protocols: a review
Security of device-independent quantum key distribution protocols: a review Open
Device-independent quantum key distribution (DI-QKD) is often seen as the ultimate key exchange protocol in terms of security, as it can be performed securely with uncharacterised black-box devices. The advent of DI-QKD closes several loop…
View article: Robustness of implemented device-independent protocols against constrained leakage
Robustness of implemented device-independent protocols against constrained leakage Open
Device-independent (DI) protocols have experienced significant progress in recent years, with a series of demonstrations of DI randomness generation or expansion, as well as DI quantum key distribution. However, existing security proofs fo…
View article: Improved DIQKD protocols with finite-size analysis
Improved DIQKD protocols with finite-size analysis Open
The security of finite-length keys is essential for the implementation of device-independent quantum key distribution (DIQKD). Presently, there are several finite-size DIQKD security proofs, but they are mostly focused on standard DIQKD pr…
View article: Fidelity bounds for device-independent advantage distillation
Fidelity bounds for device-independent advantage distillation Open
It is known that advantage distillation (that is, information reconciliation using two-way communication) improves noise tolerances for quantum key distribution (QKD) setups. Two-way communication is hence also of interest in the device-in…
View article: Quantum Chernoff divergence in advantage distillation for quantum key distribution and device-independent quantum key distribution
Quantum Chernoff divergence in advantage distillation for quantum key distribution and device-independent quantum key distribution Open
Device-independent quantum key distribution (DIQKD) aims to mitigate adversarial exploitation of imperfections in quantum devices, by providing an approach for secret key distillation with modest security assumptions. Advantage distillatio…
View article: Lipschitz continuity of quantum-classical conditional entropies with respect to angular distance and related properties
Lipschitz continuity of quantum-classical conditional entropies with respect to angular distance and related properties Open
We derive a Lipschitz continuity bound for quantum-classical conditional entropies with respect to angular distance, with a Lipschitz constant that is independent of the dimension of the conditioning system. This bound is sharper in some s…
View article: Device-independent uncloneable encryption
Device-independent uncloneable encryption Open
Uncloneable encryption, first introduced by Broadbent and Lord (TQC 2020) is a quantum encryption scheme in which a quantum ciphertext cannot be distributed between two non-communicating parties such that, given access to the decryption ke…
View article: Security of device-independent quantum key distribution protocols: a review
Security of device-independent quantum key distribution protocols: a review Open
Device-independent quantum key distribution (DI-QKD) is often seen as the ultimate key exchange protocol in terms of security, as it can be performed securely with uncharacterised black-box devices. The advent of DI-QKD closes several loop…
View article: A device-independent protocol for XOR oblivious transfer
A device-independent protocol for XOR oblivious transfer Open
Oblivious transfer is a cryptographic primitive where Alice has two bits and Bob wishes to learn some function of them. Ideally, Alice should not learn Bob's desired function choice and Bob should not learn any more than what is logic…
View article: Prospects for device-independent quantum key distribution
Prospects for device-independent quantum key distribution Open
Device-independent quantum key distribution (DIQKD) aims to achieve secure key distribution with only minimal assumptions, by basing its security on the violation of Bell inequalities. While this offers strong security guarantees, it comes…