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4,228 results · page 168 of 177
Donald Beaver, Joan Feigenbaum, Victor Shoup
No abstract is available for this record.
Tatsuaki Okamoto, Kazuo Ohta
No abstract is available for this record.
André Chailloux, Iordanis Kerenidis
In quantum zero knowledge, the assumption was made that the verifier is only using unitary operations. Under this assumption, many nice properties have been shown about quantum zero knowledge, including the fact that Honest-Verifier Quantum Statistical Zero Knowledge ($HVQSZK$) is equal to Cheating-Verifier Quantum Statistical Zero Knowledge ($QSZK$) (see ~\cite{Wat02,Wat06}). In this paper, we study what happens when we allow an honest verifier to flip some coins in addition to using unitary operations. Flipping a coin is a non-unitary operation but doesn\'t seem at first to enhance the cheating possibilities of the verifier since a classical honest verifier can flip coins. In this setting, we show an unexpected result: any classical Interactive Proof has an Honest-Verifier Quantum Statistical Zero Knowledge proof with coins. Note that in the classical case, honest verifier $SZK$ is no more powerful than $SZK$ and hence it is not believed to contain even $NP$. On the other hand, in the case of cheating verifiers, we show that Quantum Statistical Zero Knowledge where the verifier applies any non-unitary operation is equal to Quantum Zero-Knowledge where the verifier uses only unitaries. One can think of our results in two complementary ways. If we would like to use the honest verifier model as a means to study the general model by taking advantage of their equivalence, then it is imperative to use the unitary definition without coins, since with the general one this equivalence is most probably not true. On the other hand, if we would like to use quantum zero knowledge protocols in a cryptographic scenario where the honest-but-curious model is sufficient, then adding the unitary constraint severely decreases the power of quantum zero knowledge protocols.
Atsushi Takahashi
<!-- *** Custom HTML *** --> We associate to a regular system of weights a weighted projective line over an algebraically closed field of characteristic zero in two different ways. One is defined as a quotient stack via a hypersurface singularity for a regular system of weights and the other is defined via the signature of the same regular system of weights. The main result in this paper is that if a regular system of weights is of dual type then these two weighted projective lines have equivalent abelian categories of coherent sheaves. As a corollary, we can show that the triangulated categories of the graded singularity associated to a regular system of weights has a full exceptional collection, which is expected from homological mirror symmetries. The main theorem of this paper will be generalized to more general one, to the case when a regular system of weights is of genus zero, which will be given in [5]. Since we need more detailed study of regular systems of weights and some knowledge of algebraic geometry of Deligne–Mumford stacks there, the author write a part of the result in this paper to which another simple proof based on the idea by Geigle–Lenzing [2] can be applied.
Mike Burmester, Fred Piper, Yvo Desmedt, Michael J. Walker
No abstract is available for this record.
Gilles Brassard, Claude Crépeau
No abstract is available for this record.
Tatsuaki Okamoto, Kazuo Ohta
No abstract is available for this record.
Moti Yung
No abstract is available for this record.
Mihir Bellare, Silvio Micali
No abstract is available for this record.
Joan Boyar, René Peralta
No abstract is available for this record.
Yacov Yacobi, Zahava Shmuely
No abstract is available for this record.
Adi Shamir
No abstract is available for this record.
Mihir Bellare, Shafi Goldwasser
No abstract is available for this record.
Jens Groth, Steve Lu
No abstract is available for this record.
NAHUM A. FREEDBERG
In the differential diagnosis of supraventricular tachycardia, pacing maneuvers or observation rarely provide a diagnosis when used individually.1 The introduction of transcatheter therapy for cardiac arrhythmia transforms electrophysiology from an exclusive, scholarly, almost Talmudic, field to an interventional goal-oriented field where successful elimination of the arrhythmia by “burning” often serves as “proof” of the arrhythmia mechanism (Learning by Burning). In a series of papers by Callans et al.2–4 published in this Journal, the term “learning while burning” was coined, emphasizing that in contrast to the goal oriented approach, ablation procedure is indeed a powerful tool for understanding the interplay between anatomical substrate and the pathophysiology of clinical arrhythmia. The authors in the present Journal article5 put a new twist on that concept by utilizing junctional beats induced during ablation procedure of AV nodal slow pathway modification to gain a new insight to the differential diagnosis of atrioventricular node reentry tachycardia (AVNRT) versus junctional tachycardia (JT). The authors should be applauded for a meticulous execution of the study protocol and a rigorous validation of their findings that showed convincingly that the mean H-A during JT is shorter than the mean H-A during AVNRT and that the mean delta H-A (defined as retrograde H-A during ventricular pacing minus H-A during tachycardia) is negative during AVNRT, as opposed to positive during JT. In the study design, both AVNRT and JT were induced in each patient. When these measurements were compared on an individual basis (meaning that every patient's measurements during AVNRT were compared with his or her own measurements during JT controlling for variability between patients), these findings hold true in most patients (see Figs. 2 and 3). How can we explain these finding based on our present knowledge about the electrophysiological properties of these arrhythmias? AVNRT is the most common cause of supraventricular tachycardia in patients referred for electrophysiological study (EPS).1 The “common,”“typical,”“slow-fast” type is present in over 80% of all cases of AVNRT.6 In a simplistic model, AVNRT results from reentry involving two anatomically distinct AV node structures7,8 (i.e., “slow” and “fast” pathways). In “slow-fast” AVNRT, the reentry circuit consists of anterograde conduction through the slow pathway and retrograde conduction by the fast pathway with the earliest retrograde atrial activation in the “fast pathway region” at the apex of the triangle of Koch, recorded on the His-bundle electrogram from the right septum.9,10 Unfortunately, life is not that simple: the three-dimensional anatomy and cytoarchitecture of the AV junction is complex11,12 and the exact location of the atrionodal connections and slow and fast pathways are still controversial. Although several elegant models based on functional characteristics of different areas of the compact AV node and surrounding structures were proposed to explain dual-AV node physiology, the sheer bulk of the literature on the subject and the ongoing debate attest that none of them is proven.13,14 In as many as 40% of the patients with AVNRT, there are multiple AV nodal pathways.15 Even in patients with typical AVNRT, recording with close-spaced electrodes in the His, coronary sinus (CS), and the slow-pathway areas has shown that there is heterogeneity of the retrograde fast pathway conduction pattern.16 Recording of the His bundle potential from the right and left sides of the septum has shown that the earliest retrograde atrial activation during AVNRT is most often recorded on the left side of the septum.17 Thus, it is not surprising that there is a considerable variability in H-A intervals in patients with typical AVNRT, making it difficult at times to differentiate between typical AVNRT and other arrhythmias (including JT) based on H-A interval alone. According to the slow-fast pathway model, the retrograde atrial activation sequence during right ventricular pacing at the tachycardia cycle length, immediately after typical AVNRT, propagates retogradely from the His bundle through the lower common pathway to the fast pathway, and should be similar to the activation sequence during typical AVNRT. Retrograde H-A interval during ventricular pacing (H-Ap; measured from the end of the most proximal His potential to earliest A) is the sum of retrograde conduction time of the lower common pathway and the retrograde fast pathway. The H-A of typical AVNRT (H-At) according to this model is retrograde conduction time of the fast pathway minus anterograde conduction time of the lower common pathway. The difference between H-Ap and H-At (so called delta H-A) equals retrograde plus anterograde conduction time of the lower common pathway13 (assuming that the retrograde fast pathway conduction time is identical during pacing and AVNRT). A positive delta HA suggests that a lower common pathway is present. A negative delta HA, which, in fact, was found in the present study5 and by others,18 cannot be explained by this simple model. Although there are several explanations for this phenomenon, including difference in conduction velocity, activation path,19 and a combination thereof,13 a negative delta HA probably reflects a very short or an absent lower common pathway. Automatic JT as described by Coumel20 is a rare arrhythmia seen mainly in the pediatric population21 and postcardiac surgery21,22 and very rarely in adults.23 In the few cases studied, abnormal automaticity within or in close proximity to the His bundle was found.24–26 JT is frequently seen during radio frequency ablation using the AV node modification by slow pathway approach. In fact, the presence of JT is associated with successful slow pathway ablation.27,28 The pathophysiology of JT during ablation is thought to be enhanced automaticity due to heating of the tissue29,30 or local release of norepinephrine.31 Studies in pig and rabbit heart models have shown that heating in a discrete area located in the middle of the triangle of Koch that was located in close proximity to the compact AV node induced JT. In that area, no slow pathway potential was seen and it was distant from the site of earliest retrograde atrial activation. There was a large variation between individual animals regarding the location of these sites.30 In canine blood-perfused atrioventricular node preparations, JT was induced by heating anterior to the CS os with the earliest retrograde atrial activation site at the His-potential recording site or in the middle of Koch's triangle. After interruption of the posterior input to the AV node, atrial activation during JT spread from the low posterior to the high anterior septum.29 In humans, VA block during junctional ectopy is a harbinger of AV block in patients undergoing RF ablation of the slow pathway,27 suggesting that the retrograde atrial activation during JT may involve the His area or the common lower pathway. However, in that same paper, the authors observed that “VA conduction should be expected during the junctional ectopy that accompanies slow pathway ablation, even when there is poor VA conduction during baseline ventricular pacing,” and that the AV block was proximal to the His.27 These astute observations suggest that the site of VA conduction during JT is proximal to site of VA block during ventricular pacing. Wagshal et al.32 reported that higher temperature lesions simultaneously abolish all slow pathway activity as well as the focus of JT, which suggests that the JT source is located or triggered by slow pathway tissue. In a study by Lee et al.,33 atrial activation sequences were assessed by comparing H-A interval (measured at the high right atrium) during various forms of AVNRT and JT induced by ablation. In 27 patients with slow-fast AVNRT, H-A during JT was shorter than during AVNRT: 58 ± 24 msec compared with 68 ± 21 msec, respectively (P < 0.01). In the present study,5 a similar trend in mean H-A interval was observed: 35 msec versus 54 msec during JT and AVNRT, respectively. These findings call into question the concept that JT seen during RF ablation originates or has an exit point near the His area as described in the rare “de novo” automatic JT.24 Obviously, if a junctional beat originates near the His, distally to a common pathway, the H-A interval during JT will be longer than H-A interval during AVNRT that has a more proximal turn-around point to the fast pathway. In that situation, one would expect near-zero delta H-A in JT and positive delta H-A in AVNRT—in contrast to the finding of present5 and other33 studies. Studies in animal models and high resolution mapping in humans have demonstrated several mechanisms that can account for the shorter H-A interval during JT compared with AVNRT: changes in activation sequences that may cause direct activation of the atria, compact AV node,29 anisotropic spread from one more AV nodal transitional zone,34 fibers connecting to the fast pathway,35 or fibers connecting the slow pathway ablation area directly to the fast pathway in a more proximal location.33 Local heating may cause an increase in conduction velocity due to a direct effect30 or adrenergic stimulation. A recent study in a canine complete AV block model has shown that the application of RF energy caused a shift from the distal portion of the AV junctional area to a more proximal one. This enhanced junctional automaticity was suppressed by esmolol but not affected by atropine.31 In conclusion, differential diagnosis of a short RP tachycardia can be challenging. The paper by Srivathsan et al.5 adds a valuable new technique regarding the diagnosis of JT versus AVNRT, as well as provides insight into the electrophysiological mechanism of this fascinating and elusive arrhythmia. Further research is needed to ascertain whether these findings can be extended to the clinical forms of JT. Acknowledgment: The author would like to thank Dr. Shaul Atar for critical review of the manuscript.
Éric Filiol
This paper presents a protocol aiming at proving that an encryption system contains structural weaknesses without disclosing any information on those weaknesses. A verifier can check in a polynomial time that a given property of the cipher system output has been effectively realized. This property has been chosen by the prover in such a way that it cannot been achieved by known attacks or exhaustive search but only if the prover indeed knows some undisclosed weaknesses that may effectively endanger the cryptosystem security. This protocol has been denoted zero-knowledge-like proof of cryptanalysis. In this paper, we apply this protocol to the Bluetooth core encryption algorithm E0, used in many mobile environments and thus we suggest that its security can seriously be put into question.
Charles Rackoff, Daniel Simón
No abstract is available for this record.
Toshiya Itoh, Yuji Ohta, Hiroki Shizuya
No abstract is available for this record.
Jens Groth, Rafail Ostrovsky
No abstract is available for this record.
Kazuo Ohta, Tatsuaki Okamoto, Atsushi Fujioka
No abstract is available for this record.
Ivan Damgård
No abstract is available for this record.
Ivan Damgård
No abstract is available for this record.
Tatsuaki Okamoto, David Chaum, Kazuo Ohta
No abstract is available for this record.
Iftach Haitner, Omer Reingold
Interactive hashing, introduced by Naor, Ostrovsky, Venkatesan, and Yung (J. Cryptol. 11(2):87–108, 1998 ), plays an important role in many cryptographic protocols. In particular, interactive hashing is a major component in all known constructions of statistically hiding commitment schemes and of statistical zero-knowledge arguments based on general one-way permutations/functions. Interactive hashing with respect to a one-way function f is a two-party protocol that enables a sender who knows y = f ( x ) to transfer a random hash z = h ( y ) to a receiver such that the sender is committed to y : the sender cannot come up with x and x ′ such that f ( x )≠ f ( x ′), but h ( f ( x ))= h ( f ( x ′))= z . Specifically, if f is a permutation and h is a two-to-one hash function, then the receiver does not learn which of the two preimages { y , y ′}= h −1 ( z ) is the one the sender can invert with respect to f . This paper reexamines the notion of interactive hashing, and proves the security of a variant of the Naor et al. protocol, which yields a more versatile interactive hashing theorem. When applying our new proof to (an equivalent variant of) the Naor et al. protocol, we get an alternative proof for this protocol that seems simpler and more intuitive than the original one, and achieves better parameters (in terms of how security preserving the reduction is).