arXiv subjects

Roohallah Rastaghi

Publications and source records attributed to Roohallah Rastaghi.

7 recordsLinked to original sources

arXiv2014

New Approach for CCA2-Secure Post-Quantum Cryptosystem Using Knapsack Problem

Chosen-ciphertext security, which guarantees confidentiality of encrypted messages even in the presence of a decryption oracle, has become the defacto notion of security for public-key encryption under active attack. In this manuscript, for the first time, we propose a new approach for constructing post-quantum cryptosystems secure against adaptive chosen ciphertext attack (CCA2-secure) in the standard model using the knapsack problem. The computational version of the knapsack problem is NP-hard. Thus, this problem is expected to be difficult to solve using quantum computers. Our construction is a precoding-based encryption algorithm and uses the knapsack problem to perform a permutation and pad some random fogged data to the message bits. Compared to other approaches were introduced today, our approach is very simple and more efficient.

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arXiv2013

Cryptanalysis of a New Knapsack Type Public-Key Cryptosystem

Recently, Hwang et al. introduced a knapsack type public-key cryptosystem. They proposed a new algorithm called permutation combination algorithm. By exploiting this algorithm, they attempt to increase the density of knapsack to avoid the low-density attack. We show that this cryptosystem is not secure, as it based on basic Merkel-Hellman knapsack cryptosystem and because of the superincreasing structure, we can use shamir's attack on the basic Merkel-Hellman knapsack to break this cryptosystem.

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arXiv2013

An Efficient CCA2-Secure Variant of the McEliece Cryptosystem in the Standard Model

Recently, a few chosen-ciphertext secure (CCA2-secure) variants of the McEliece public-key encryption (PKE) scheme in the standard model were introduced. All the proposed schemes are based on encryption repetition paradigm and use general transformation from CPA-secure scheme to a CCA2-secure one. Therefore, the resulting encryption scheme needs \textit{separate} encryption and has \textit{large} key size compared to the original scheme, which complex public key size problem in the code-based PKE schemes. Thus, the proposed schemes are not sufficiently efficient to be used in practice. In this work, we propose an efficient CCA2-secure variant of the McEliece PKE scheme in the standard model. The main novelty is that, unlike previous approaches, our approach is a generic conversion and can be applied to \textit{any} one-way trapdoor function (OW-TDF), the lowest-level security notion in the context of public-key cryptography, resolving a big fundamental and central problem that has remained unsolved in the past two decades.

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arXiv2013

An Efficient Encryption Algorithm for P2P Networks Robust Against Man-in-the-Middle Adversary

Peer-to-peer (P2P) networks have become popular as a new paradigm for information exchange and are being used in many applications such as file sharing, distributed computing, video conference, VoIP, radio and TV broadcasting. This popularity comes with security implications and vulnerabilities that need to be addressed. Especially duo to direct communication between two end nodes in P2P networks, these networks are potentially vulnerable to "Man-in-the-Middle" attacks. In this paper, we propose a new public-key cryptosystem for P2P networks that is robust against Man-in-the-Middle adversary. This cryptosystem is based on RSA and knapsack problems. Our precoding-based algorithm uses knapsack problem for performing permutation and padding random data to the message. We show that comparing to other proposed cryptosystems, our algorithm is more efficient and it is fully secure against an active adversary.

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arXiv2013

Cryptanalysis and Improvement of Akleylek et al.'s cryptosystem

Akleylek et al. [S. Akleylek, L. Emmungil and U. Nuriyev, A mod ified algorithm for peer-to-peer security, journal of Appl. Comput. Math., vol. 6(2), pp.258-264, 2007.], introduced a modified public-key encryption scheme with steganographic approach for security in peer-to-peer (P2P) networks. In this cryptosystem, Akleylek et al. attempt to increase security of the P2P networks by mixing ElGamal cryptosystem with knapsack problem. In this paper, we present a ciphertext-only attack against their system to recover message. In addition, we show that for their scheme completeness property is not holds, and therefore, the receiver cannot uniquely decrypts messages. Furthermore, we also show that this system is not chosen-ciphertext secure, thus the proposed scheme is vulnerable to man-in-the-middle-attack, one of the most pernicious attacks against P2P networks. Therefore, this scheme is not suitable to implement in the P2P networks. We modify this cryptosystem in order to increase its security and efficiency. Our construction is the efficient CCA2-secure variant of the Akleylek et al.'s encryption scheme in the standard model, the de facto security notion for public-key encryption schemes.

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arXiv2013

URDP: General Framework for Direct CCA2 Security from any Lattice-Based PKE Scheme

Design efficient lattice-based cryptosystem secure against adaptive chosen ciphertext attack (IND-CCA2) is a challenge problem. To the date, full CCA2-security of all proposed lattice-based PKE schemes achieved by using a generic transformations such as either strongly unforgeable one-time signature schemes (SU-OT-SS), or a message authentication code (MAC) and weak form of commitment. The drawback of these schemes is that encryption requires "separate encryption". Therefore, the resulting encryption scheme is not sufficiently efficient to be used in practice and it is inappropriate for many applications such as small ubiquitous computing devices with limited resources such as smart cards, active RFID tags, wireless sensor networks and other embedded devices. In this work, for the first time, we introduce an efficient universal random data padding (URDP) scheme, and show how it can be used to construct a "direct" CCA2-secure encryption scheme from "any" worst-case hardness problems in (ideal) lattice in the standard model, resolving a problem that has remained open till date. This novel approach is a "black-box" construction and leads to the elimination of separate encryption, as it avoids using general transformation from CPA-secure scheme to a CCA2-secure one. IND-CCA2 security of this scheme can be tightly reduced in the standard model to the assumption that the underlying primitive is an one-way trapdoor function.

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arXiv2012

Cryptanalysis of a Public-key Cryptosystem Using Lattice Basis Reduction Algorithm

We proposed a new attack against Hwang et al.'s cryptosystem. This cryptosystem uses a super-increasing sequence as private key and the authors investigate a new algorithm called permutation combination algorithm to enhance density of knapsack to avoid the low-density attack. Sattar J. Aboud [Aboud j. Sattar, "An improved knapsack public key cryptography system", International Journal of Internet Technology and Secured Transactions, Vol.3 (3), pp.310-319, 2011] used Shamir's attack on the basic Merkle-Hellman cryptosystem to break this cryptosystem. In this paper, we introduce a direct attack against Hwang et al.'s cryptosystem based on Lattice basis reduction algorithms. By computing complexity of propose attack, we show that unlike Aboud's cryptanalysis, our cryptanalysis is more efficient and practicable.

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