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Low cost Radio Frequency IDentification (RFID) tags are increasingly being deployed in various practical applications these days. Security analysis of the way these tags are used in an application is a must for successful adoption of the RFID technology. Depending on the requirements of the particular application, security demands on these tags cover some or all of the aspects such as privacy, untraceability and authentication. As a result of increasing deployment of RFID tags, many works on RFID protocols and their security analysis have appeared in the literature in the past few years. Although most protocol proposals also provide some justification for the claimed security properties of these protocols, independent third party evaluation has often revealed weaknesses in these protocols. In this work, we present a third party security evaluation of a recently proposed Lightweight Mutual Authentication Protocol (LMAP ++). Mutual authentication protocols are an important class of protocols for RFID applications. In these protocols, the reader and the tag of an RFID system run an interactive game to authenticate themselves to each other. In this work, we present traceability and desynchronization attacks against the protocol LMAP ++. First we show that LMAP ++ does not satisfy the security notion of traceability as defined in the model proposed by Jules and Weis. Using the ideas of this traceability attack, next we show that LMAP ++ also suffers from a desynchronization attack. The presented attacks have low complexities and high success probabilities. To the best of our knowledge, this the first attack on the LMAP ++ protocol. © 2011 ICITST.

World University root node

Department of Computer Science & Engineering

2011 International Conference for Internet Technology and Secured Transactions, ICITST 2011

Security analysis of LMAP ++, an RFID authentication protocol

Many RFID protocols use cryptographic hash functions for their security. The resource constrained nature of RFID systems forces the use of light weight cryptographic algorithms. Tav-128 is one such 128-bit light weight hash function proposed by Peris-Lopez et al. for a low-cost RFID tag authentication protocol. Apart from some statistical tests for randomness by the designers themselves, Tav-128 has not undergone any other thorough security analysis. Based on these tests, the designers claimed that Tav-128 does not posses any trivial weaknesses. In this article, we carry out the first third party security analysis of Tav-128 and show that this hash function is neither collision resistant nor second preimage resistant. Firstly, we show a practical collision attack on Tav-128 having a complexity of 237 calls to the compression function and produce message pairs of arbitrary length which produce the same hash value under this hash function. We then show a second preimage attack on Tav-128 which succeeds with a complexity of 262 calls to the compression function. Finally, we study the constituent functions of Tav-128 and show that the concatenation of nonlinear functions A and B produces a 64-bit permutation from 32-bit messages. This could be a useful light weight primitive for future RFID protocols. © 2010 Springer-Verlag Berlin Heidelberg.

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

Cryptanalysis of Tav-128 hash function

We perform a combinatorial analysis of the SHA-2 compression function. This analysis explains in a unified way the recent attacks against reduced round SHA-2. We start with a general class of local collisions and show that the previously used local collision by Nikolić and Biryukov (NB) and Sanadhya and Sarkar (SS) are special cases. The study also clarifies several advantages of the SS local collision over the NB local collision. Deterministic constructions of up to 22-round SHA-2 collisions are described using the SS local collision and up to 21-round SHA-2 collisions are described using the NB local collision. For 23 and 24-round SHA-2, we describe a general strategy and then apply the SS local collision to this strategy. The resulting attacks are faster than those proposed by Indesteege et al using the NB local collision. We provide colliding message pairs for 22, 23 and 24-round SHA-2. Although these attacks improve upon the existing reduced round SHA-256 attacks, they do not threaten the security of the full SHA-2 family. 1 © 2009 Springer Science + Business Media, LLC.

Cryptography and Communications

A combinatorial analysis of recent attacks on step reduced SHA-2 family

In this work, we study several properties of the SHA-2 design which have been utilized in recent collision attacks against reduced round SHA-2. Small modifications to the SHA-2 design are suggested to thwart these attacks. The modified round function provides the same resistance to linearization attacks as the original SHA-2 round function, but, provides better resistance to non-linear attacks. Our next contribution is to introduce the general idea of "multiple feed-forward" for the construction of cryptographic hash functions. This can provide increased resistance to the Chabaud-Joux type "perturbation-correction" collision attacks. The idea of feed-forward is taken further by introducing the idea of feed-forward across message blocks leading to resistance against generic multi-collision attacks. The net effect of the suggested changes to the SHA-2 design has insignificant impact on the efficiency of computing the digest. Copyright 2009 ACM.

Proceedings of the 4th International Symposium on ACM Symposium on Information, Computer and Communications Security, ASIACCS'09

A new hash family obtained by modifying the SHA-2 family

Most of the attacks against (reduced) SHA-2 family in literature have used local collisions which are valid for linearized version of SHA-2 hash functions. Recently, at FSE '08, an attack against reduced round SHA-256 was presented by Nikolić and Biryukov which used a local collision which is valid for the actual SHA-256 function. It is a 9-step local collision which starts by introducing a modular difference of 1 in the two messages. It succeeds with probability roughly 1/3. We build on the work of Nikolić and Biryukov and provide a generalized nonlinear local collision which accepts an arbitrary initial message difference. This local collision succeeds with probability 1. Using this local collision we present attacks against 18-step SHA-256 and 18-step SHA-512 with arbitrary initial difference. Both of these attacks succeed with probability 1. We then present special cases of our local collision and show two different differential paths for attacking 20-step SHA-256 and 20-step SHA-512. One of these paths is the same as presented by Nikolić and Biryukov while the other one is a new differential path. Messages following both these differential paths can be found with probability 1. This improves on the previous result where the success probability of 20-step attack was 1/3. Finally, we present two differential paths for 21-step collisions for SHA-256 and SHA-512, one of which is a new path. The success probabilities of these paths for SHA-256 are roughly 2-∈15 and 2-∈17 which improve on the 21-step attack having probability 2-∈19 reported earlier. We show examples of message pairs following all the presented differential paths for up to 21-step collisions in SHA-256. We also show first real examples of colliding message pairs for up to 20-step reduced SHA-512. © 2008 Springer-Verlag Berlin Heidelberg.

Non-linear reduced round attacks against SHA-2 Hash family

Recently, at FSE '08, Nikolić and Biryukov introduced a new technique for analyzing SHA-2 round function. Building on their work, but using other differential paths, we construct two different deterministic attacks against 21-step SHA-2 hash family. Since the attacks are deterministic, they are actually combinatorial constructions of collisions. There are six free words in our first construction. This gives exactly 2192 different collisions for 21-step SHA-256 and exactly 2384 different collisions for 21-step SHA-512. The second construction has five free words. The best previous result, due to Nikolić and Biryukov, for finding collisions for 21-step SHA-256 holds with probability 2-∈19. No results on 21-step SHA-512 are previously known. Further, we provide evidence that the Nikolić-Biryukov differential path is unlikely to yield 21-step collisions for SHA-512. © 2008 Springer-Verlag Berlin Heidelberg.

Deterministic constructions of 21-step collisions for the SHA-2 hash family

The SHA-256 hash function has started getting attention recently by the cryptanalysis community due to the various weaknesses found in its predecessors such as MD4, MD5, SHA-0 and SHA-1. We make two contributions in this work. First we describe message modification techniques and use them to obtain an algorithm to generate message pairs which collide for the actual SHA-256 reduced to 18 steps. Our second contribution is to present differential paths for 19, 20, 21, 22 and 23 steps of SHA-256. We construct parity check equations in a novel way to find these characteristics. Further, the 19-step differential path presented here is constructed by using only 15 local collisions, as against the previously known 19-step near collision differential path which consists of interleaving of 23 local collisions. Our 19-step differential path can also be seen as a single local collision at the message word level. We use a linearized local collision in this work. These results do not cause any threat to the security of the SHA-256 hash function. © 2008 Springer-Verlag Berlin Heidelberg.

Attacking reduced round SHA-256

In this work, we provide new and improved attacks against 22, 23 and 24-step SHA-2 family using a local collision given by Sanadhya and Sarkar (SS) at ACISP '08. The success probability of our 22-step attack is 1 for both SHA-256 and SHA-512. The computational efforts for the 23-step and 24-step SHA-256 attacks are respectively 211.5 and 228.5 calls to the corresponding step reduced SHA-256. The corresponding values for the 23 and 24-step SHA-512 attack are respectively 216.5 and 232.5 calls. Using a look-up table having 232 (resp. 264) entries the computational effort for finding 24-step SHA-256 (resp. SHA-512) collisions can be reduced to 215.5 (resp. 222.5) calls. We exhibit colliding message pairs for 22, 23 and 24-step SHA-256 and SHA-512. This is the first time that a colliding message pair for 24-step SHA-512 is provided. The previous work on 23 and 24-step SHA-2 attacks is due to Indesteege et al. and utilizes the local collision presented by Nikolić and Biryukov (NB) at FSE '08. The reported computational efforts are 218 and 228.5 for 23 and 24-step SHA-256 respectively and 2 43.9 and 253 for 23 and 24-step SHA-512. The previous 23 and 24-step attacks first constructed a pseudo-collision and later converted it into a collision for the reduced round SHA-2 family. We show that this two step procedure is unnecessary. Although these attacks improve upon the existing reduced round SHA-2 attacks, they do not threaten the security of the full SHA-2 family. © 2008 Springer Berlin Heidelberg.

New collision attacks against up to 24-step SHA-2

Although a fuzzy rule based system offers interpretability, its application in gene expression data analysis becomes difficult due to the very high dimensional nature of the data. Here we propose an interesting scheme of combining fuzzy modeling with neural networks for designing fuzzy rule based classifiers for gene expression data analysis. A neural system is used for selecting a set of informative genes. Considering only these selected set of genes, we cluster the expression data with a fuzzy clustering algorithm. Each cluster is then converted into a fuzzy if-then rule, which models an area in the input space. These rules are tuned using a gradient descent technique to improve the classification performance. The rule base is tested on a leukemia data set containing two classes and it is found to produce good results. We propose some simple criteria to simplify membership functions and the rules. Our rule extraction scheme can be automated. Unlike other classifiers, it produces human interpretable rules which are not expected to give poor generalization because fuzzy rules do not respond to areas not represented by the training data. The last two properties are very important for problems like diagnosis of cancer. © 2008 - IOS Press.

Journal of Intelligent and Fuzzy Systems

Deriving meaningful rules from gene expression data for classification

Hydrophobicity is probably the most important property of amino acid that is being often exploited o predict protein folds. There are many amino acid hydrophobicity scales available in the literature. Here we propose two computational approaches based on self-organizing map (SOM) and fuzzy clustering to find some consensus scales. Although SOM and fuzzy clustering produce centroids, we propose new schemes to compute more effective representative scales that exploit the properties of SOM and fuzzy memberships. To demonstrate the utility of the new scales, we apply them to predict the protein folds of a benchmark data set using neural networks. Our experiments show that it is possible to generate useful scales with better utility compared to some existing scales. There can be other applications of the proposed scales. © Dynamic Publishers, Inc.

Neural, Parallel and Scientific Computations

Computation of consensus hydrophobicity scales with self-organizing maps and fuzzy clustering along with applications to protein fold prediction

The starting point for collision attacks on practical hash functions is a local collision. In this paper, we make a systematic study of local collisions for the SHA-2 family. The possible linear approximations of the constituent Boolean functions are considered and certain impossible conditions for such approximations are identified. Based on appropriate approximations, we describe a general method for finding local collisions. Applying this method, we obtain several local collisions and compute the probabilities of the various differential paths. Previously, only one local collision due to Gilbert-Handschuh was known. We point out two impossible conditions in the GH local collision and provide an example of an impossible differential path for linearized SHA-2 using this local collision. Sixteen new local collisions are obtained none of which have any impossible conditions. The probabilities of these local collisions are a little less than the GH local collision. On the other hand, the absence of impossible conditions may make them more suitable for (reduced round) collision search attacks on the SHA-2 family. © Springer-Verlag Berlin Heidelberg 2007.

New local collisions for the SHA-2 hash family

In this work, an accurate method for real time assessment of tool wear in face milling based on the cutting force signals using support vector machine learning is presented. New combinations of signal processing techniques are used to extract relevant signal features, which are robust against random process variations, external chance disturbances and presence of outliers, from the acquired data. Relationship between the extracted features and the observed values of tool wear is built using the support vector regression technique. This machine learning algorithm is accurate and robust for estimation of complex and non-linear relationship among the process variables. Grid search method is adopted to select the optimum model parameters. The developed models are validated on unseen testing data for their predicting capabilities. Significant results are obtained using the proposed method for both laboratory and industrial data.

Proceedings of the IEEE International Conference on Industrial Technology

Support vector regression based tool wear assessment in face milling

Many attempts have been made to analyze gene expression data. Typical goals of such analysis include discovery of subclasses, designing predictors/classifiers for diseases, identifying marker genes, and trying to get a deeper understanding of underlying biological process. Success of each of these tasks strongly depends on the features used to solve the problem. The high dimensional nature of expression profiles makes the task very difficult. Consequently, many researchers have used some feature selection criteria to reduce the dimensionality of the problem. These approaches are off-line in nature, as feature selection is done in a separate phase from the system design phase. These approaches ignore the fact that utility of features depends on both the problem that is solved and the tool that is used to solve the problem. We here propose to use a novel neural scheme that picks up the necessary features on-line when the system learns the classification task. Because it considers all the features at one go, it does not miss any subtle combination of these features. We demonstrate the effectiveness of our on-line feature selection (OFS) scheme to distinguish between acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) cancer expression data set. Our scheme could identify only five genes that can produce results as good as or even better than what is reported in the literature on this data set. It identifies an important marker gene that alone has a very good discriminating power. This analysis method is quite general in nature and can be effectively used in other areas of bioinformatics. © 2006 Wiley Periodicals, Inc.