Computational Indistinguishability between Quantum States and Its Cryptographic Application

We introduce a computational problem of distinguishing between two specific quantum states as a new cryptographic problem to design a quantum cryptographic scheme that is "secure" against any polynomial-time quantum adversary. Our problem, QSCDff, is to distinguish between two types of random coset states with a hidden permutation over the symmetric group of finite degree. This naturally generalizes the commonly-used distinction problem between two probability distributions in computational cryptography. As our major contribution, we show that QSCDff has three properties of cryptographic interest: (i) QSCDff has a trapdoor; (ii) the average-case hardness of QSCDff coincides with its worst-case hardness; and (iii) QSCDff is computationally at least as hard as the graph automorphism problem in the worst case. These cryptographic properties enable us to construct a quantum public-key cryptosystem, which is likely to withstand any chosen plaintext attack of a polynomial-time quantum adversary. We further discuss a generalization of QSCDff, called QSCDcyc, and introduce a multi-bit encryption scheme that relies on similar cryptographic properties of QSCDcyc.Comment: 24 pages, 2 figures. We improved presentation, and added more detail proofs and follow-up of recent wor

Reexamination of Quantum Bit Commitment: the Possible and the Impossible

Bit commitment protocols whose security is based on the laws of quantum mechanics alone are generally held to be impossible. In this paper we give a strengthened and explicit proof of this result. We extend its scope to a much larger variety of protocols, which may have an arbitrary number of rounds, in which both classical and quantum information is exchanged, and which may include aborts and resets. Moreover, we do not consider the receiver to be bound to a fixed "honest" strategy, so that "anonymous state protocols", which were recently suggested as a possible way to beat the known no-go results are also covered. We show that any concealing protocol allows the sender to find a cheating strategy, which is universal in the sense that it works against any strategy of the receiver. Moreover, if the concealing property holds only approximately, the cheat goes undetected with a high probability, which we explicitly estimate. The proof uses an explicit formalization of general two party protocols, which is applicable to more general situations, and a new estimate about the continuity of the Stinespring dilation of a general quantum channel. The result also provides a natural characterization of protocols that fall outside the standard setting of unlimited available technology, and thus may allow secure bit commitment. We present a new such protocol whose security, perhaps surprisingly, relies on decoherence in the receiver's lab.Comment: v1: 26 pages, 4 eps figures. v2: 31 pages, 5 eps figures; replaced with published version; title changed to comply with puzzling Phys. Rev. regulations; impossibility proof extended to protocols with infinitely many rounds or a continuous communication tree; security proof of decoherence monster protocol expanded; presentation clarifie

Real Life Cryptology

A large number of enciphered documents survived from early modern Hungary. This area was a particularly fertile territory where cryptographic methods proliferated, because a large portion of the population was living in the frontier zone, and participated (or was forced to participate) in the network of the information flow. A quantitative analysis of sixteenth-century to seventeenth-century Hungarian ciphers (300 cipher keys and 1,600 partly or entirely enciphered letters) reveals that besides the dominance of diplomatic use of cryptography, there were many examples of “private” applications too. This book reconstructs the main reasons and goals why historical actors chose to use ciphers in a diplomatic letter, a military order, a diary or a private letter, what they decided to encrypt, and how they perceived the dangers threatening their messages

How Many Glyphs and How Many Scribes? Digital Paleography and the Voynich Manuscript

It can be safely claimed that there is no medieval script that has been seen, analyzed, and debated more than that of the mysterious and as-yet-unread Voynich Manuscript (Beinecke MS 408). For centuries, bibliophiles, linguists, codicologists, art historians, and amateur cryptologists have pored over the manuscript, examining it from every angle, debating every wormhole, arguing over every stain and crease. Some things we know: the invented script is comprised of carefully-written glyphs without precedent or obvious model; forensic material evidence has determined that the parchment, ink, and pigments date from the early 15th century; the provenance trail is nearly unbroken from the seventeenth century to today. But we still don’t know how to read it, in spite of new theories flying across the internet on a near-weekly basis. “Voynichologists” disagree as to some of the most important and basic questions about the manuscript. How many letterforms are there? How many scribes can be identified? Are there ligatures, majuscules, abbreviations, and other scribal conventions? These questions have never been satisfactorily answered. Using digital paleographic methodologies including the Archetype (DigiPal) application and other annotation tools, this project will revisit the paleographic analyses of the Voynich glyphs to propose answers to some of these questions and discuss how these answers open avenues for further research

Venice's secret service: Organising intelligence in the renaissance. Introduction

Venice's Secret Service is the untold and arresting story of the world's earliest centrally-organised state intelligence service. Long before the inception of SIS and the CIA, in the period of the Renaissance, the Republic of Venice had masterminded a remarkable centrally-organised state intelligence organisation that played a pivotal role in the defence of the Venetian empire. Housed in the imposing Doge's Palace and under the direction of the Council of Ten, the notorious governmental committee that acted as Venice's spy chiefs, this 'proto-modern' organisation served prominent intelligence functions including operations (intelligence and covert action), analysis, cryptography and steganography, cryptanalysis, and even the development of lethal substances. Official informants and amateur spies were shipped across Europe, Anatolia, and Northern Africa, conducting Venice's stealthy intelligence operations. Revealing a plethora of secrets, their keepers, and their seekers, Venice's Secret Service explores the social and managerial processes that enabled their existence and that furnished the foundation for an extraordinary intelligence organisation created by one of the early modern world's most cosmopolitan states

SoK: Acoustic Side Channels

We provide a state-of-the-art analysis of acoustic side channels, cover all the significant academic research in the area, discuss their security implications and countermeasures, and identify areas for future research. We also make an attempt to bridge side channels and inverse problems, two fields that appear to be completely isolated from each other but have deep connections.Comment: 16 page