Nishant Doshi

Hidden access structure ciphertext policy attribute based encryption with constant length ciphertext

In Cipher text Policy Attribute Based Encryption (CP-ABE) scheme, a user is able to decrypt the cipher text only if the pre-specified access structure (also called ciphertext policy) in the ciphertext, matches the attributes defined in the secret key. However, the limitation of the scheme is that the receivers anonymity is sacrificed as the access structure of the ciphertext reveals the same. The obvious solution to this problem as proposed by proposed by Nishide et al, is to hide ciphertext-policy (hidden access structure). However, although this solution uses reasonably computable decryption policies, it generates the ciphertext of size that is at least, linearly varying with the number of attributes. It also requires additional pairing operations during decryption. We attempt to overcome these limitations in the proposed scheme viz. Ciphertext Policy Attribute Based Encryption with Constant Length (CP-ABE-CL). In our scheme, the ciphertext and secret key remain constant in length, irrespective of the number of attributes chosen. In addition, the decryption algorithm requires fewer and fixed number of pairing operations. Our scheme works for a threshold case: the number of attributes (excluding wildcard attributes) in a policy must be a subset of attributes in a secret key. The proposed scheme supports the positive, negative and wildcard attributes in policy.

Fully secure ciphertext policy attribute-based encryption with constant length ciphertext and faster decryption

In PKC 2010, Herranz et al. proposed the first fully threshold ciphertext policy attribute-based encryption CP-ABE scheme with constant length ciphertext. However, their scheme is selectively secure with respect to the chosen plaintext attack. They have left three open problems for CP-ABE with constant ciphertext length, that is, Security against the Chosen Ciphertext Attacks, Security Reduction to a better mathematical problem and to make the scheme Fully Secure. Indeed, in ACISP 2012, Ge et al. proposed the solutions to the first two problems but left their proposed scheme selective secure. This makes their scheme weaker because it is secure only for a particular policy. With an aim to propose a fully secure constant ciphertext length CP-ABE scheme, in this paper, we discuss our attempts at extending the approach of Lewko et al. in EUROCRYPT 2010. The scheme that we propose here allows any subset of attributes of the secret key as a part of the ciphertext policy. Copyright

Constant ciphertext length in multi-authority Ciphertext Policy Attribute Based Encryption

In Ciphertext Policy Attribute Based Encryption (CP-ABE)a previously defined association between the attributes of a user and the ciphertext associated with these attributes is exploited to determine the secret key of the user. However, for a user with multiple attributes, the length of the key depends on the number of attributes. The existing methods that use reasonably computable decryption policies produce the ciphertext of size at least linearly varying with the number of attributes. In this paper, we propose two schemes. One scheme is of variable length based on Bethencourt et al. construction. In second scheme, the ciphertext remains constant in length, irrespective of the number of attributes. It works for a threshold case: the number of attributes in a policy must be a subset of attributes in a secret key. The security of scheme is based on Decisional Bilinear Diffie-Hellman (DBDH) problem.

An analytical study of biometric based remote user authentication schemes using smart cards

Abstract In this digital era, any two entities can exchange messages, irrespective of their physical distance, via an authentication scheme on the Internet. A biometric identity is one of the unique parameters of each human being. A smart card stores such parameters based on the characteristics of an entity. Although a smart card cannot be tamper resistant, specific attacks have been identified by researchers in the context of remote user authentication schemes. Thus, motivated, we have conducted in this paper a state-of-art survey, the first of its type, on remote user authentication schemes from their inception. We have summarized and discussed distinct attacks that are likely to occur on a remote user authentication scheme and how such an attack makes a system vulnerable. Our aim is not only to document the history of findings on remote user authentication schemes but also to familiarize researchers with the list of attacks that have been identified to date.

A password based authentication scheme for wireless multimedia systems

In this digital era, where Internet of Things (IoT) is increasing day by day, use of resource constrained devices is also increasing. Indeed, the features such as low cost, less maintenance, more adaptive to hostile environment, etc. make the wireless multimedia devices to be the best choice as the resource constrained devices. For the security, the end user device requires to establish the session key with the server before transferring the data. Mobile is one of the device having more and more usage as wireless multimedia device in recent years. In 2013, Li et al. proposed an efficient scheme for the wireless mobile communications and claimed it to be secure against various attacks. Recently, Shen et al. claimed that the scheme of Li et al. is still vulnerable to the privileged insider attack, the stolen verifier attack and finally proposed a scheme to withstand the mentioned and other attacks. However, in this paper we claim that the scheme of Shen et al. is still susceptible to the user anonymity, the session specific temporary information attack and the replay attack. In addition, Shen et al.’s scheme requires more time due to many operations. Further, we propose an efficient scheme that is secure against various known attacks and due to reduced time complexity our scheme is a preferred choice for the wireless mobile networks and hence for wireless multimedia systems.

A survey on attacks in remote user authentication scheme

Remote user authentication scheme is designed to provide facility of system access at different places without any disturbance. Communication should be secured and verified in remote user authentication. There are various schemes available in which smart card, password, and biometric features are used for authentication. Thus, many researchers introduced different attacks in authentication scheme. We made state of art survey on three different schemes which are Chang-Chengs scheme, Li-Weng-Fans scheme and Adelas scheme in this paper. In addition, we summarized three different schemes based on their performance.

AB-OR: Improving the Efficiency in Onion Routing Using Attribute Based Cryptography

Onion routing has been employed as a technique for ensuring anonymous communication over a public channel to ensure the integrity of the message as well as the privacy of the contending entities amidst untrusted routers. The technique ensures that the actual data as well as the meta-data in the packet are hidden from the prying intermediaries. It uses multiple layers of encryption of the packet for the purpose. However, exactly due to the same, the efficiency concerns in onion routing have to be addressed. In this paper, we propose and demonstrate the use of the Ciphertext Policy Attribute Based Encryption (CP-ABE) to improve the overhead in the existing onion routing schemes as well as to improve their overall security strength. Moreover, we also impart failure tolerance in case an Onion Router in the communication path breaks down. We formally call the proposed approach as AB-OR (Attribute Based Onion Routing).

An efficient approach for privacy preserving distributed mining of association rules in unsecured environment

Distributed data mining techniques are widely used for many applications viz; marketing, decision making, statistical analysis etc. In distributed data environment, each of the involving sites contains local information which will be collaborated to extract global mining result. However, these techniques have been investigated in terms of privacy and security concerns of individual sites information. To solve this problem, many cryptography techniques have been investigated. Still there is a room for further improvement. In this paper, we propose an efficient approach for privacy preserving distributed association rule mining. We use onion routing protocol in order to exchange information among involving sites. We use an elliptic curve (EC) based cryptography in order to achieve security and privacy of individual sites information in unsecured distributed environment. Finally, we analyze proposed solution in terms of security, privacy, computational cost and communication cost.

A Novel Approach for Matrix Chain Multiplication Using Greedy Technique for Packet Processing

Matrix chain multiplication is one of well known application of optimization problem. There are N matrices of different size were given and we have to multiply them based on their row and column size. The order in which matrices are multiplied may change the number of computations. This shows the use of greedy technique to solve this problem in O(NlogN) time which we are applying for packet processing in routing.

Width of a Binary Tree

Till current date in majority books on algorithm and research papers, they talk about height of a binary tree in terms like height balanced binary tree. In this paper the notion of width of a binary tree has been introduced and later the recursive algorithm based on the traversal techniques of the binary tree is given. Later the iterative version of algorithm using the notion of stack is introduced. The width of a binary tree is defined based on the number of nodes at every level. The highest of all is the width of a binary tree. The same concept can be applied to the general tree. General Terms Algorithms