On Non-Monotonicity of the Success Probability in Linear Cryptanalysis

Like any other cryptanalytic attack, the success rate of a linear attack is expected to improve as more data becomes available. Bogdanov and Tischhauser (FSE 2013) made the rather surprising claim that the success rate of a linear attack may go down with increasing plaintext amount, after an optimal point. They supported this claim with experimental evidence by an attack on SmallPresent-20. Different explanations have been given to explain this surprising phenomenon. In this note, we give quantitative values regarding when this phenomenon can be observed. We conclude that it should not be an issue for attacks in practice except for those with a tiny bias

MILP-aided Cryptanalysis of the FUTURE Block Cipher

FUTURE is a recently proposed, lightweight block cipher. It has an AES-like, SP-based, 10-round encryption function, where, unlike most other lightweight constructions, the diffusion layer is based on an MDS matrix. Despite its relative complexity, it has a remarkable hardware performance due to careful design decisions. In this paper, we conducted a MILP-based analysis of the cipher, where we incorporated exact probabilities rather than just the number of active S-boxes into the model. Through the MILP analysis, we were able to find differential and linear distinguishers for up to 5 rounds of FUTURE, extending the known distinguishers of the cipher by one round

On Hierarchical Threshold Secret Sharing

Recently, two novel schemes have been proposed for hierarchical threshold secret sharing, one based on Birkoff interpolation and another based on bivariate Lagrange interpolation. In this short paper, we propose a much simpler solution for this problem

Generic Construction of Trace and Revoke Schemes

Broadcast encryption (BE) is a cryptographic primitive that allows a broadcaster to encrypt digital content to a privileged set of users and in this way prevent revoked users from accessing the content. In BE schemes, a group of users, called traitor s may leak their keys and enable an adversary to receive the content. Such malicious users can be detected through traitor tracing (TT) schemes. The ultimate goal in a content distribution system would be combining traitor tracing and broadcast encryption (resulting in a trace and revoke system) so that any receiver key found to be compromised in a tracing process would be revoked from future transmissions. In this paper, we propose a generic method to transform a broadcast encryption scheme into a trace and revoke scheme. This transformation involves the utilization of a fingerprinting code over the underlying BE transmission. While fingerprinting codes have been used for constructing traitor tracing schemes in the past, their usage has various shortcomings such as the increase of the public key size with a linear factor in the length of the code. Instead, we propose a novel way to apply fingerprinting codes that allows for efficient parameters while retaining the traceability property. Our approach is based on a new property of fingerprinting codes we introduce, called public samplability. We have instantiated our generic transformation with the BE schemes of [4, 13, 20] something that enables us to produce trace and revoke schemes with novel properties. Specifically, we show (i) a trace and revoke scheme with constant private key size and short ciphertext size, (ii) the first ID-based trace and revoke scheme, (iii) the first publicly traceable scheme with constant private key size and (iv) the first trace and revoke scheme against pirate rebroadcasting attack in the public key setting

Non-invasive diagnostic tests for Helicobacter pylori infection

BACKGROUND: Helicobacter pylori (H pylori) infection has been implicated in a number of malignancies and non-malignant conditions including peptic ulcers, non-ulcer dyspepsia, recurrent peptic ulcer bleeding, unexplained iron deficiency anaemia, idiopathic thrombocytopaenia purpura, and colorectal adenomas. The confirmatory diagnosis of H pylori is by endoscopic biopsy, followed by histopathological examination using haemotoxylin and eosin (H & E) stain or special stains such as Giemsa stain and Warthin-Starry stain. Special stains are more accurate than H & E stain. There is significant uncertainty about the diagnostic accuracy of non-invasive tests for diagnosis of H pylori. OBJECTIVES: To compare the diagnostic accuracy of urea breath test, serology, and stool antigen test, used alone or in combination, for diagnosis of H pylori infection in symptomatic and asymptomatic people, so that eradication therapy for H pylori can be started. SEARCH METHODS: We searched MEDLINE, Embase, the Science Citation Index and the National Institute for Health Research Health Technology Assessment Database on 4 March 2016. We screened references in the included studies to identify additional studies. We also conducted citation searches of relevant studies, most recently on 4 December 2016. We did not restrict studies by language or publication status, or whether data were collected prospectively or retrospectively. SELECTION CRITERIA: We included diagnostic accuracy studies that evaluated at least one of the index tests (urea breath test using isotopes such as13C or14C, serology and stool antigen test) against the reference standard (histopathological examination using H & E stain, special stains or immunohistochemical stain) in people suspected of having H pylori infection. DATA COLLECTION AND ANALYSIS: Two review authors independently screened the references to identify relevant studies and independently extracted data. We assessed the methodological quality of studies using the QUADAS-2 tool. We performed meta-analysis by using the hierarchical summary receiver operating characteristic (HSROC) model to estimate and compare SROC curves. Where appropriate, we used bivariate or univariate logistic regression models to estimate summary sensitivities and specificities. MAIN RESULTS: We included 101 studies involving 11,003 participants, of which 5839 participants (53.1%) had H pylori infection. The prevalence of H pylori infection in the studies ranged from 15.2% to 94.7%, with a median prevalence of 53.7% (interquartile range 42.0% to 66.5%). Most of the studies (57%) included participants with dyspepsia and 53 studies excluded participants who recently had proton pump inhibitors or antibiotics.There was at least an unclear risk of bias or unclear applicability concern for each study.Of the 101 studies, 15 compared the accuracy of two index tests and two studies compared the accuracy of three index tests. Thirty-four studies (4242 participants) evaluated serology; 29 studies (2988 participants) evaluated stool antigen test; 34 studies (3139 participants) evaluated urea breath test-13C; 21 studies (1810 participants) evaluated urea breath test-14C; and two studies (127 participants) evaluated urea breath test but did not report the isotope used. The thresholds used to define test positivity and the staining techniques used for histopathological examination (reference standard) varied between studies. Due to sparse data for each threshold reported, it was not possible to identify the best threshold for each test.Using data from 99 studies in an indirect test comparison, there was statistical evidence of a difference in diagnostic accuracy between urea breath test-13C, urea breath test-14C, serology and stool antigen test (P = 0.024). The diagnostic odds ratios for urea breath test-13C, urea breath test-14C, serology, and stool antigen test were 153 (95% confidence interval (CI) 73.7 to 316), 105 (95% CI 74.0 to 150), 47.4 (95% CI 25.5 to 88.1) and 45.1 (95% CI 24.2 to 84.1). The sensitivity (95% CI) estimated at a fixed specificity of 0.90 (median from studies across the four tests), was 0.94 (95% CI 0.89 to 0.97) for urea breath test-13C, 0.92 (95% CI 0.89 to 0.94) for urea breath test-14C, 0.84 (95% CI 0.74 to 0.91) for serology, and 0.83 (95% CI 0.73 to 0.90) for stool antigen test. This implies that on average, given a specificity of 0.90 and prevalence of 53.7% (median specificity and prevalence in the studies), out of 1000 people tested for H pylori infection, there will be 46 false positives (people without H pylori infection who will be diagnosed as having H pylori infection). In this hypothetical cohort, urea breath test-13C, urea breath test-14C, serology, and stool antigen test will give 30 (95% CI 15 to 58), 42 (95% CI 30 to 58), 86 (95% CI 50 to 140), and 89 (95% CI 52 to 146) false negatives respectively (people with H pylori infection for whom the diagnosis of H pylori will be missed).Direct comparisons were based on few head-to-head studies. The ratios of diagnostic odds ratios (DORs) were 0.68 (95% CI 0.12 to 3.70; P = 0.56) for urea breath test-13C versus serology (seven studies), and 0.88 (95% CI 0.14 to 5.56; P = 0.84) for urea breath test-13C versus stool antigen test (seven studies). The 95% CIs of these estimates overlap with those of the ratios of DORs from the indirect comparison. Data were limited or unavailable for meta-analysis of other direct comparisons. AUTHORS' CONCLUSIONS: In people without a history of gastrectomy and those who have not recently had antibiotics or proton ,pump inhibitors, urea breath tests had high diagnostic accuracy while serology and stool antigen tests were less accurate for diagnosis of Helicobacter pylori infection.This is based on an indirect test comparison (with potential for bias due to confounding), as evidence from direct comparisons was limited or unavailable. The thresholds used for these tests were highly variable and we were unable to identify specific thresholds that might be useful in clinical practice.We need further comparative studies of high methodological quality to obtain more reliable evidence of relative accuracy between the tests. Such studies should be conducted prospectively in a representative spectrum of participants and clearly reported to ensure low risk of bias. Most importantly, studies should prespecify and clearly report thresholds used, and should avoid inappropriate exclusions

Use and outcomes of amplatz renal dilator for treatment of urethral strictures

ABSTRACT Introduction Urethral stricture disease is still a major problem in men. Many procedures are available for the treatment of urethral strictures; urethral dilatation is one of the oldest. The blind dilatation of urethral strictures may be a difficult and potentially dangerous procedure. The purpose of this study was to describe safe urethral dilatation using amplatz renal dilator and to report outcomes. Materials and Methods From 2010 to 2014, a total of 26 men with primary urethral strictures were managed by urethral dilatation using amplatz renal dilators. The parameters analyzed included presentation of patients, retrograde urethrography (RGU) findings, pre-and postoperative maximum flow rate (Qmax) on uroflowmetry (UF) and post-void residual urine (PVR). Patients were followed-up at 1.6 and 12 months. The technique described in this paper enables such strictures to be safely dilated after endoscopic placement of a suitable guidewire and stylet over which amplatz renal dilators are introduced. Results The mean age of the patients was 57.6 (35–72) years. The median stricture length was 0.82 (0.6–1.5)cm. Pre-operative uroflowmetry showed Qmax of 7.00 (4–12) mL/sec and ultrasonography showed PVR of 75.00 (45–195)mL. Postoperatively, Qmax improved to 18.00 (15–22)mL/sec (p<0.001) at 1 month, 17.00 (13–21)mL/sec (p<0.001) at 6 months and 15.00 (12–17)mL/sec (p<0.001) at 12 months. The post-operative PVR values were 22.50 (10–60)mL (p<0.001), 30.00 (10–70)mL (p<0.001) and 30.00 (10–70) mL (p<0.001) at 1.6 12 months, respectively. The median procedure time was 15.00 (12–22) minutes. None of the patients had a recurrence during a 12-month period of follow-up. Conclusion Urethral dilatation with amplatz renal dilators avoids the risks associated with blind dilatation techniques. This tecnique is a safe, easy, well-tolerated and cost-effective alternative for treatment of urethral strictures

Reputation-Based Trust Management for P2P Networks

The open and anonymous nature of a P2P network makes it an ideal medium for attackers to spread malicious content. In this paper, we describe a reputationbased trust management protocol for P2P networks where users rate the reliability of parties they deal with, and share this information with their peers. The protocol helps establishing trust among good peers as well as identifying the malicious ones