Cryptography

25 pages, 729 KiB

Open AccessArticle

Flat ORAM: A Simplified Write-Only Oblivious RAM Construction for Secure Processors

by Syed Kamran Haider and Marten van Dijk

Cryptography 2019, 3(1), 10; https://doi.org/10.3390/cryptography3010010 - 25 Mar 2019

Cited by 6 | Viewed by 7469

Oblivious RAM (ORAM) is a cryptographic primitive which obfuscates the access patterns to a storage, thereby preventing privacy leakage. So far in the current literature, only ‘fully functional’ ORAMs are widely studied which can protect, at a cost of considerable performance penalty, against [...] Read more.

Oblivious RAM (ORAM) is a cryptographic primitive which obfuscates the access patterns to a storage, thereby preventing privacy leakage. So far in the current literature, only ‘fully functional’ ORAMs are widely studied which can protect, at a cost of considerable performance penalty, against the strong adversaries who can monitor all read and write operations. However, recent research has shown that information can still be leaked even if only the write access pattern (not reads) is visible to the adversary. For such weaker adversaries, a fully functional ORAM turns out to be an overkill, causing unnecessary overheads. Instead, a simple ‘write-only’ ORAM is sufficient, and, more interestingly, is preferred as it can offer far better performance and energy efficiency than a fully functional ORAM. In this work, we present Flat ORAM: an efficient write-only ORAM scheme which outperforms the closest existing write-only ORAM called HIVE. HIVE suffers from performance bottlenecks while managing the memory occupancy information vital for correctness of the protocol. Flat ORAM introduces a simple idea of Occupancy Map (OccMap) to efficiently manage the memory occupancy information resulting in far better performance. Our simulation results show that, compared to HIVE, Flat ORAM offers

50 %

performance gain on average and up to

80 %

energy savings. Full article

(This article belongs to the Section Hardware Security)

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13 pages, 747 KiB

Open AccessArticle

A New Class of Strongly Asymmetric PKA Algorithms: SAA-5

by Luigi Accardi, Satoshi Iriyama, Koki Jimbo and Massimo Regoli

Cryptography 2019, 3(1), 9; https://doi.org/10.3390/cryptography3010009 - 20 Mar 2019

Cited by 1 | Viewed by 5563

Abstract

A new class of public key agreement (PKA) algorithms called strongly-asymmetric algorithms (SAA) was introduced in a previous paper by some of the present authors. This class can be shown to include some of the best-known PKA algorithms, for example the Diffie–Hellman and [...] Read more.

A new class of public key agreement (PKA) algorithms called strongly-asymmetric algorithms (SAA) was introduced in a previous paper by some of the present authors. This class can be shown to include some of the best-known PKA algorithms, for example the Diffie–Hellman and several of its variants. In this paper, we construct a new version of the previous construction, called SAA-5, improving it in several points, as explained in the Introduction. In particular, the construction complexity is reduced, and at the same time, robustness is increased. Intuitively, the main difference between SAA-5 and the usual PKA consists of the fact that in the former class, B (Bob) has more than one public key and A (Alice) uses some of them to produce her public key and others to produce the secret shared key (SSK). This introduces an asymmetry between the sender of the message (B) and the receiver (A) and motivates the name for this class of algorithms. After describing the main steps of SAA-5, we discuss its breaking complexity assuming zero complexity of discrete logarithms and the computational complexity for both A and B to create SSK. Full article

11 pages, 239 KiB

Open AccessArticle

An Improved Identity-Based Multivariate Signature Scheme Based on Rainbow

by Le Van Luyen

Cryptography 2019, 3(1), 8; https://doi.org/10.3390/cryptography3010008 - 17 Mar 2019

Cited by 6 | Viewed by 7026

Abstract

Multivariate Public Key Cryptography (MPKC) is one of the main candidates for post-quantum cryptography, especially in the area of signature schemes. In this paper, we instantiate a certificate Identity-Based Signature (IBS) scheme based on Rainbow, one of the most efficient and secure multivariate [...] Read more.

Multivariate Public Key Cryptography (MPKC) is one of the main candidates for post-quantum cryptography, especially in the area of signature schemes. In this paper, we instantiate a certificate Identity-Based Signature (IBS) scheme based on Rainbow, one of the most efficient and secure multivariate signature schemes. In addition, we revise the previous identity-based signature scheme IBUOV based on the Unbalanced Oil and Vinegar (UOV) scheme on the security and choice of parameters and obtain that our scheme is more efficient than IBUOV in terms of key sizes and signature sizes. Full article

(This article belongs to the Special Issue Post-Quantum Cryptography: From Theoretical Foundations to Practical Deployments)

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22 pages, 5176 KiB

Open AccessArticle

Automating Privacy Compliance Using Policy Integrated Blockchain

by Karuna Pande Joshi and Agniva Banerjee

Cryptography 2019, 3(1), 7; https://doi.org/10.3390/cryptography3010007 - 05 Feb 2019

Cited by 6 | Viewed by 8960

Abstract

An essential requirement of any information management system is to protect data and resources against breach or improper modifications, while at the same time ensuring data access to legitimate users. Systems handling personal data are mandated to track its flow to comply with [...] Read more.

An essential requirement of any information management system is to protect data and resources against breach or improper modifications, while at the same time ensuring data access to legitimate users. Systems handling personal data are mandated to track its flow to comply with data protection regulations. We have built a novel framework that integrates semantically rich data privacy knowledge graph with Hyperledger Fabric blockchain technology, to develop an automated access-control and audit mechanism that enforces users’ data privacy policies while sharing their data with third parties. Our blockchain based data-sharing solution addresses two of the most critical challenges: transaction verification and permissioned data obfuscation. Our solution ensures accountability for data sharing in the cloud by incorporating a secure and efficient system for End-to-End provenance. In this paper, we describe this framework along with the comprehensive semantically rich knowledge graph that we have developed to capture rules embedded in data privacy policy documents. Our framework can be used by organizations to automate compliance of their Cloud datasets. Full article

(This article belongs to the Special Issue Advances of Blockchain Technology and Its Applications)

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13 pages, 2005 KiB

Open AccessArticle

A Novel Algorithm of Constructing Highly Nonlinear S-p-boxes

by Yasir Naseer, Tariq Shah, Dawood Shah and Sadam Hussain

Cryptography 2019, 3(1), 6; https://doi.org/10.3390/cryptography3010006 - 16 Jan 2019

Cited by 27 | Viewed by 7187

Abstract

The role of substitution boxes is very important in block ciphers. Substitution boxes are utilized to create confusion in the cryptosystem. However, to create both confusion and diffusion in any cryptosystem p-boxes and chaos base substitution boxes are designed. In this work, a [...] Read more.

The role of substitution boxes is very important in block ciphers. Substitution boxes are utilized to create confusion in the cryptosystem. However, to create both confusion and diffusion in any cryptosystem p-boxes and chaos base substitution boxes are designed. In this work, a simple method is presented that serves both ways. This method is based on composition of the action of symmetric group on Galois field and inversion map. This construction method provides a large number of highly non-linear substitution permutation boxes having the property of confusion as well as diffusion. These substitution permutation boxes have all the cryptography properties. Their utilization in the image encryption application is measured by majority logic criterion. We named these newly designed substitution boxes (S-boxes) as substitution permutation boxes (S-p-boxes), because they serve as both substitution boxes (S-boxes) as well as permutation boxes (p-boxes). Full article

(This article belongs to the Section Hardware Security)

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2 pages, 189 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Cryptography in 2018

by Cryptography Editorial Office

Cryptography 2019, 3(1), 5; https://doi.org/10.3390/cryptography3010005 - 12 Jan 2019

Viewed by 5809

Abstract

Rigorous peer-review is the corner-stone of high-quality academic publishing [...] Full article

11 pages, 299 KiB

Open AccessArticle

Cryptanalysis of Round-Reduced Fantomas, Robin and iSCREAM

by Ashutosh Dhar Dwivedi, Shalini Dhar, Gautam Srivastava and Rajani Singh

Cryptography 2019, 3(1), 4; https://doi.org/10.3390/cryptography3010004 - 10 Jan 2019

Cited by 13 | Viewed by 7007

Abstract

In this work, we focus on LS-design ciphers Fantomas, Robin, and iSCREAM. LS-designs are a family of bitslice ciphers aimed at efficient masked implementations against side-channel analysis. We have analyzed Fantomas and Robin with a technique that previously has not been applied to [...] Read more.

In this work, we focus on LS-design ciphers Fantomas, Robin, and iSCREAM. LS-designs are a family of bitslice ciphers aimed at efficient masked implementations against side-channel analysis. We have analyzed Fantomas and Robin with a technique that previously has not been applied to both algorithms or linear cryptanalysis. The idea behind linear cryptanalysis is to build a linear characteristic that describes the relation between plaintext and ciphertext bits. Such a relationship should hold with probability 0.5 (bias is zero) for a secure cipher. Therefore, we try to find a linear characteristic between plaintext and ciphertext where bias is not equal to zero. This non-random behavior of cipher could be converted to some key-recovery attack. For Fantomas and Robin, we find 5 and 7-round linear characteristics. Using these characteristics, we attack both the ciphers with reduced rounds and recover the key for the same number of rounds. We also apply linear cryptanalysis to the famous CAESAR candidate iSCREAM and the closely related LS-design Robin. For iScream, we apply linear cryptanalysis to the round-reduced cipher and find a 7-round best linear characteristics. Based on those linear characteristics we extend the path in the related-key scenario for a higher number of rounds. Full article

(This article belongs to the Special Issue Authenticated Encryption)

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16 pages, 883 KiB

Open AccessArticle

Applications of Blockchain Technology in Medicine and Healthcare: Challenges and Future Perspectives

by Asad Ali Siyal, Aisha Zahid Junejo, Muhammad Zawish, Kainat Ahmed, Aiman Khalil and Georgia Soursou

Cryptography 2019, 3(1), 3; https://doi.org/10.3390/cryptography3010003 - 02 Jan 2019

Cited by 294 | Viewed by 35488

Abstract

Blockchain technology has gained considerable attention, with an escalating interest in a plethora of numerous applications, ranging from data management, financial services, cyber security, IoT, and food science to healthcare industry and brain research. There has been a remarkable interest witnessed in utilizing [...] Read more.

Blockchain technology has gained considerable attention, with an escalating interest in a plethora of numerous applications, ranging from data management, financial services, cyber security, IoT, and food science to healthcare industry and brain research. There has been a remarkable interest witnessed in utilizing applications of blockchain for the delivery of safe and secure healthcare data management. Also, blockchain is reforming the traditional healthcare practices to a more reliable means, in terms of effective diagnosis and treatment through safe and secure data sharing. In the future, blockchain could be a technology that may potentially help in personalized, authentic, and secure healthcare by merging the entire real-time clinical data of a patient’s health and presenting it in an up-to-date secure healthcare setup. In this paper, we review both the existing and latest developments in the field of healthcare by implementing blockchain as a model. We also discuss the applications of blockchain, along with the challenges faced and future perspectives. Full article

(This article belongs to the Special Issue Advances of Blockchain Technology and Its Applications)

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25 pages, 877 KiB

Open AccessArticle

New Cryptanalytic Attack on RSA Modulus N = pq Using Small Prime Difference Method

by Muhammad Rezal Kamel Ariffin, Saidu Isah Abubakar, Faridah Yunos and Muhammad Asyraf Asbullah

Cryptography 2019, 3(1), 2; https://doi.org/10.3390/cryptography3010002 - 20 Dec 2018

Cited by 10 | Viewed by 8644

Abstract

This paper presents new short decryption exponent attacks on RSA, which successfully leads to the factorization of RSA modulus

N = p q

in polynomial time. The paper has two parts. In the first part, we report the usage of the small prime [...] Read more.

This paper presents new short decryption exponent attacks on RSA, which successfully leads to the factorization of RSA modulus

N = p q

in polynomial time. The paper has two parts. In the first part, we report the usage of the small prime difference method of the form

| b^{2} p - a^{2} q | < N^{γ}

where the ratio of

\frac{q}{p}

is close to

\frac{b^{2}}{a^{2}}

, which yields a bound

d < \frac{\sqrt{3}}{\sqrt{2}} N^{\frac{3}{4} - γ}

from the convergents of the continued fraction expansion of

\frac{e}{N - ⌈ \frac{a^{2} + b^{2}}{a b} \sqrt{N} ⌉ + 1}

. The second part of the paper reports four cryptanalytic attacks on t instances of RSA moduli

N_{s} = p_{s} q_{s}

for

s = 1, 2, \dots, t

where we use

N - ⌈ \frac{a^{2} + b^{2}}{a b} \sqrt{N} ⌉ + 1

as an approximation of

ϕ (N)

satisfying generalized key equations of the shape

e_{s} d - k_{s} ϕ (N_{s}) = 1

,

e_{s} d_{s} - k ϕ (N_{s}) = 1

,

e_{s} d - k_{s} ϕ (N_{s}) = z_{s}

, and

e_{s} d_{s} - k ϕ (N_{s}) = z_{s}

for unknown positive integers

d, k_{s}, d_{s}, k_{s}

, and

z_{s}

, where we establish that t RSA moduli can be simultaneously factored in polynomial time using combinations of simultaneous Diophantine approximations and lattice basis reduction methods. In all the reported attacks, we have found an improved short secret exponent bound, which is considered to be better than some bounds as reported in the literature. Full article

12 pages, 359 KiB

Open AccessArticle

Further Observations on SIMON and SPECK Block Cipher Families

by Seyed Mojtaba Dehnavi

Cryptography 2019, 3(1), 1; https://doi.org/10.3390/cryptography3010001 - 20 Dec 2018

Cited by 4 | Viewed by 7273

Abstract

SIMON and SPECK families of block ciphers are well-known lightweight ciphers designed by the NSA. In this note, based on the previous investigations on SIMON, a closed formula for the squared correlations and differential probabilities of the mapping [...] Read more.

SIMON and SPECK families of block ciphers are well-known lightweight ciphers designed by the NSA. In this note, based on the previous investigations on SIMON, a closed formula for the squared correlations and differential probabilities of the mapping

ϕ (x) = x ⊙ S^{1} (x)

on

F_{2}^{n}

is given. From the aspects of linear and differential cryptanalysis, this mapping is equivalent to the core quadratic mapping of SIMON via rearrangement of coordinates and EA -equivalence. Based on the proposed explicit formula, a full description of DDT and LAT of

ϕ

is provided. In the case of SPECK, as the only nonlinear operation in this family of ciphers is addition mod

2^{n}

, after reformulating the formula for linear and differential probabilities of addition mod

2^{n}

, straightforward algorithms for finding the output masks with maximum squared correlation, given the input masks, as well as the output differences with maximum differential probability, given the input differences, are presented. By the aid of the tools given in this paper, the process of the search for linear and differential characteristics of SIMON and SPECK families of block ciphers could be sped up, and the complexity of linear and differential attacks against these ciphers could be reduced. Full article

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