Universally-composable privacy amplification from causality constraints

Using Hash-Based Signatures to Bootstrap Quantum Key Distribution

Quantum Key Distribution is a secret distribution technique that requires an authenticated channel. This channel is usually created on top of an un-authenticated communication medium using unconditionally secure Message Authentication Codes (MAC) and an initial common secret. We examine the consequences of replacing this MAC algorithm by a cryptographic hash-based signature algorithm, like the Lamport algorithm. We show that provided one-way functions exist, the Lamport algorithm or its variants can be instantiated in a secure way in the Universally Composable sense, and can therefore be plugg…

将不定因果序过程映射为时空中的可组合量子协议

Mapping indefinite causal order processes to composable quantum protocols in a spacetime

本研究将不定因果序过程（QC-QC）映射为时空中的因果盒，证明其可细粒度化为具有明确因果顺序的量子操作，从而恢复物理实验的可组合性，并强调相对论因果性与Fock空间的作用。

General Security Definition and Composability for Quantum & Classical Protocols

We generalize the universally composable definition of Canetti to the Quantum World. The basic idea is the same as in the classical world. The main contribution is that we unfold the result in a new model which is well adapted to quantum protocols. We also simplify some aspects of the classical case. In particular, the case of protocols with an arbitrary number of layers of sub-protocols is naturally covered in the proposed model.

Lightweight authentication for quantum key distribution

Quantum key distribution (QKD) enables unconditionally secure communication between distinct parties using a quantum channel and an authentic public channel. Reducing the portion of quantum-generated secret keys, that is consumed during the authentication procedure, is of significant importance for improving the performance of QKD systems. In the present work, we develop a lightweight authentication protocol for QKD based on a `ping-pong' scheme of authenticity check for QKD. An important feature of this scheme is that the only one authentication tag is generated and transmitted during each of…

What does the operator algebra of quantum statistics tell us about the objective causes of observable effects?

Quantum physics can only make statistical predictions about possible measurement outcomes, and these predictions originate from an operator algebra that is fundamentally different from the conventional definition of probability as a subjective lack of information regarding the physical reality of the system. In the present paper, I explore how the operator formalism accommodates the vast number of possible states and measurements by characterizing its essential function as a description of causality relations between initial conditions and subsequent observations. It is shown that any complete…

Full security of quantum key distribution from no-signaling constraints

We analyze a cryptographic protocol for generating a distributed secret key from correlations that violate a Bell inequality by a sufficient amount, and prove its security against eavesdroppers, constrained only by the assumption that any information accessible to them must be compatible with the non-signaling principle. The claim holds with respect to the state-of-the-art security definition used in cryptography, known as universally-composable security. The non-signaling assumption only refers to the statistics of measurement outcomes depending on the choices of measurements; hence security …

Simplified BB84 quantum key distribution secure against coherent attacks

Decoy-state quantum key distribution (QKD) has convincingly been shown the core solution to secure key exchange. While standard BB84 protocol needs to prepare and measure all states of two complementary bases, which seriously restricts its real life applications in photonic integration and high speed system. Fortunately, a simplified BB84, only sending and receiving three states, achieves the same asymptotic secret key rate compared with standard BB84 under coherent attacks. In this work, by skillfully exploiting uncertainty relation for smooth entropies, we provide the finite-key security bou…

Experimental quantum key distribution with source flaws

Decoy-state quantum key distribution (QKD) is a standard technique in current quantum cryptographic implementations. Unfortunately, existing experiments have two important drawbacks: the state preparation is assumed to be perfect without errors and the employed security proofs do not fully consider the finite-key effects for general attacks. These two drawbacks mean that existing experiments are not guaranteed to be secure in practice. Here, we perform an experiment that for the first time shows secure QKD with imperfect state preparations over long distances and achieves rigorous finite-key s…

相干单向量子密钥分发的有限密钥分析

Finite-Key Analysis for Coherent One-Way Quantum Key Distribution

本文在通用可组合框架内对COW-QKD变体进行严格的有限密钥安全分析，结合量子剩余哈希引理与Kato不等式推导密钥率公式，确保了对相干攻击的安全性并提升了密钥率，证实了其实际应用的可行性。

Practical post-processing for quantum-key-distribution experiments

Quantum key distribution (QKD) promises unconditionally secure key generation between two distant parties by wisely exploiting properties of quantum mechanics. In QKD, experimental measurements on quantum states are transformed to a secret key and this has to be done in accordance with a security proof. Unfortunately, many theoretical proofs are not readily implementable in experiments and do not consider all practical issues. Therefore, in order to bridge this "practical gap", we integrate a few existing theoretical results together with new developments, in effect producing a simple and comp…

Quantum one-time tables for unconditionally secure qubit-commitment

The commodity-based cryptography is an alternative approach to realize conventionally impossible cryptographic primitives such as unconditionally secure bit-commitment by consuming pre-established correlation between distrustful participants. A unit of such classical correlation is known as the one-time table (OTT). In this paper, we introduce a new example besides quantum key distribution in which quantum correlation is useful for cryptography. We propose a scheme for unconditionally secure qubit-commitment, a quantum cryptographic primitive forbidden by the recently proven no-masking theorem…

分布式对称密钥建立：一种可扩展的量子安全密钥分发协议

Distributed Symmetric Key Establishment: a Scalable Quantum-Safe Key Distribution Protocol

本文提出分布式对称密钥建立协议DSKE，通过秘密共享实现可扩展的量子安全密钥分发，在通用可组合安全框架下证明其信息论安全性与鲁棒性，并展示了在多种真实环境中的实现，为应对量子计算威胁提供了一种经济高效的解决方案。

Dirac equation with ultraviolet cutoff and quantum walk

The weak convergence theorems of the one- and two-dimensional simple quantum walks, SQW$^{(d)}, d=1,2$, show a striking contrast to the classical counterparts, the simple random walks, SRW$^{(d)}$. The limit distributions have novel structures such that they are inverted-bell shaped and the supports of them are bounded. In the present paper we claim that these properties of the SQW$^{(d)}$ can be explained by the theory of relativistic quantum mechanics. We show that the Dirac equation with a proper ultraviolet cutoff can provide a quantum walk model in three dimensions, where the walker has a…