Cryptanalysis of a Markov Chain Based User Authentication Scheme

Session key agreement protocol using smart card is extremely popular in client-server environment for secure communication. Remote user authentication protocol plays a crucial role in our daily life such as e-banking, bill-pay, online games, e-recharge, wireless sensor network, medical system, ubiquitous devices etc. Recently, Djellali et al. proposed a session key agreement protocol using smart card for ubiquitous devices. The main focus of this paper is to analyze security pitfalls of smart card and password based user authentication scheme. We have carefully reviewed Djellali et al.\u27s scheme and found that the same scheme suffers from several security weaknesses such as off-line password guessing attack, privileged insider attack. Moreover, we demonstrated that the Djellali et al.\u27s scheme does not provide proper security protection on the secret key of the server and presents inefficient password change phase

Rotational Cryptanalysis on MAC Algorithm Chaskey

In this paper we analyse the algorithm Chaskey - a lightweight MAC algorithm for 32-bit micro controllers - with respect to rotational cryptanalysis. We perform a related-key attack over Chaskey and find a distinguisher by using rotational probabilities. Having a message $m$ we can forge and present a valid tag for some message under a related key with probability $2^{-57}$ for 8 rounds and $2^{-86}$ for all 12 rounds of the permutation for keys in a defined weak-key class. This attack can be extended to full key recovery with complexity $2^{120}$ for the full number of rounds. To our knowledge this is the first published attack targeting all 12 rounds of the algorithm. Additionally, we generalize the Markov theory with respect to a relation between two plaintexts and not their difference and apply it for rotational pairs

A Study on Masquerade Detection

In modern computer systems, usernames and passwords have been by far the most common forms of authentication. A security system relying only on password protection is defenseless when the passwords of legitimate users are compromised. A masquerader can impersonate a legitimate user by using a compromised password. An intrusion detection system (IDS) can provide an additional level of protection for a security system by inspecting user behavior. In terms of detection techniques, there are two types of IDSs: signature-based detection and anomaly-based detection. An anomaly-based intrusion detection technique consists of two steps: 1) creating a normal behavior model for legitimate users during the training process, 2) analyzing user behavior against the model during the detection process. In this project, we concentrate on masquerade detection, a specific type of anomaly-based IDS. We have first explored suitable techniques to build a normal behavior model for masquerade detection. After studying two existing modeling techniques, N-gram frequency and hidden Markov models (HMMs), we have developed a novel approach based on profile hidden Markov models (PHMMs). Then we have analyzed these three approaches using the classical Schonlau data set. To find the best detection results, we have also conducted sensitivity analysis on the modeling parameters. However, we have found that our proposed PHMMs do not outperform the corresponding HMMs. We conjectured that Schonlau data set lacked the position information required by the PHMMs. To verify this conjecture, we have also generated several data sets with position information. Our experimental results show that when there is no sufficient training data, the PHMMs yield considerably better detection results than the iv corresponding HMMs since the generated position information is significantly helpful for the PHMMs

MergeMAC:A MAC for Authentication with Strict Time Constraints and Limited Bandwidth

This paper presents MergeMAC, a MAC that is particularly suitable for environments with strict time requirements and extremely limited bandwidth. MergeMAC computes the MAC by splitting the message into two parts. We use a pseudorandom function (PRF) to map messages to random bit strings and then merge them with a very efficient keyless function. The advantage of this approach is that the outputs of the PRF can be cached for frequently needed message parts. We demonstrate the merits of MergeMAC for authenticating messages on the CAN bus where bandwidth is extremely limited and caching can be used to recover parts of the message counter instead of transmitting it. We recommend an instantiation of the merging function MERGE and analyze the security of our construction. Requirements for a merging function are formally defined and the resulting EUF-CMA security of MergeMAC is proven

Group theory in cryptography

This paper is a guide for the pure mathematician who would like to know more about cryptography based on group theory. The paper gives a brief overview of the subject, and provides pointers to good textbooks, key research papers and recent survey papers in the area.Comment: 25 pages References updated, and a few extra references added. Minor typographical changes. To appear in Proceedings of Groups St Andrews 2009 in Bath, U