Group key establishment protocols: Pairing cryptography and verifiable secret sharing scheme

Thesis (Master)--Izmir Institute of Technology, Computer Engineering, Izmir, 2013Includes bibliographical references (leaves: 97-103)Text in English; Abstract: Turkish and Englishx, 154 leavesThe aim of this study is to establish a common secret key over an open network for a group of user to be used then symmetrical secure communication between them. There are two methods of GKE protocol which are key agreement and key distribution. Key agreement is a mechanism whereby the parties jointly establish a common secret. As to key distribution, it is a mechanism whereby one of the parties creates or obtains a secret value and then securely distributes it to other parties. In this study, both methods is applied and analyzed in two different GKE protocols. Desirable properties of a GKE are security and efficiency. Security is attributed in terms of preventing attacks against passive and active adversary. Efficiency is quantified in terms of computation, communication and round complexity. When constructing a GKE, the challenge is to provide security and efficiency according to attributed and quantified terms. Two main cryptographic tools are selected in order to handle the defined challenge. One of them is bilinear pairing which is based on elliptic curve cryptography and another is verifiable secret sharing which is based on multiparty computation. In this thesis, constructions of these two GKE protocols are studied along with their communication models, security and efficiency analysis. Also, an implementation of four-user group size is developed utilizing PBC, GMP and OpenSSL Libraries for both two protocols

An Internet-Wide Analysis of Diffie-Hellman Key Exchange and X.509 Certificates in TLS

Transport Layer Security (TLS) is a mature cryptographic protocol, but has flexibility during implementation which can introduce exploitable flaws. New vulnerabilities are routinely discovered that affect the security of TLS implementations. We discovered that discrete logarithm implementations have poor parameter validation, and we mathematically constructed a deniable backdoor to exploit this flaw in the finite field Diffie-Hellman key exchange. We described attack vectors an attacker could use to position this backdoor, and outlined a man-in-the-middle attack that exploits the backdoor to force Diffie-Hellman use during the TLS connection. We conducted an Internet-wide survey of ephemeral finite field Diffie-Hellman (DHE) across TLS and STARTTLS, finding hundreds of potentially backdoored DHE parameters and partially recovering the private DHE key in some cases. Disclosures were made to companies using these parameters, resulting in a public security advisory and discussions with the CTO of a billion-dollar company. We conducted a second Internet-wide survey investigating X.509 certificate name mismatch errors, finding approximately 70 million websites invalidated by these errors and additionally discovering over 1000 websites made inaccessible due to a combination of forced HTTPS and mismatch errors. We determined that name mismatch errors occur largely due to certificate mismanagement by web hosting and content delivery network companies. Further research into TLS implementations is necessary to encourage the use of more secure parameters

Factors Impacting Key Management Effectiveness in Secured Wireless Networks

The use of a Public Key Infrastructure (PKI) offers a cryptographic solution that can overcome many, but not all, of the MANET security problems. One of the most critical aspects of a PKI system is how well it implements Key Management. Key Management deals with key generation, key storage, key distribution, key updating, key revocation, and certificate service in accordance with security policies over the lifecycle of the cryptography. The approach supported by traditional PKI works well in fixed wired networks, but it may not appropriate for MANET due to the lack of fixed infrastructure to support the PKI. This research seeks to identify best practices in securing networks which may be applied to new network architectures

Postcards from the post-HTTP world: Amplification of HTTPS vulnerabilities in the web ecosystem

HTTPS aims at securing communication over the Web by providing a cryptographic protection layer that ensures the confidentiality and integrity of communication and enables client/server authentication. However, HTTPS is based on the SSL/TLS protocol suites that have been shown to be vulnerable to various attacks in the years. This has required fixes and mitigations both in the servers and in the browsers, producing a complicated mixture of protocol versions and implementations in the wild, which makes it unclear which attacks are still effective on the modern Web and what is their import on web application security. In this paper, we present the first systematic quantitative evaluation of web application insecurity due to cryptographic vulnerabilities. We specify attack conditions against TLS using attack trees and we crawl the Alexa Top 10k to assess the import of these issues on page integrity, authentication credentials and web tracking. Our results show that the security of a consistent number of websites is severely harmed by cryptographic weaknesses that, in many cases, are due to external or related-domain hosts. This empirically, yet systematically demonstrates how a relatively limited number of exploitable HTTPS vulnerabilities are amplified by the complexity of the web ecosystem

Towards a Cooperative Security System for Mobile-Health Applications

[EN] Mobile Health (m-Health) system architectures are typically based on mobile and wireless communications, and use mobile devices with data exchange supported by Web Services (WS). Although m-Health systems offer mobility as a potential and precious resource they also present several challenged issues and constraints, such as, battery and storage capacity, broadcast constraints, interferences, disconnections, noises, limited bandwidths, and network delays. Furthermore, constant mobility and often-required Internet connectivity also exposes and compromises the privacy and confidentiality of the m-Health system information. This paper proposes a novel data encryption solution for mobile health systems, considering a novel and early-proposed cooperation strategy. This encryption solution, called data encryption for mobile health applications (DE4MHA), tries to guarantee the best confidentiality, integrity, and authenticity of m-health systems users data. The paper also presents a performance evaluation study comparing the performance an m-Health application with and without the DE4MHA.This work has been partially supported by National Funding from the FCT - Fundacao para a Ciencia e a Tecnologia through the PEst-OE/EEI/LA0008/2013 Project; by the AAL4ALL (Ambient Assisted Living for All), project co-funded by COMPETE under FEDER via QREN Programme; by Brazilian National Council for Research and Development (CNPq) via Grant No. 309335/2017-5; and by FINEP, with resources from Funttel, Grant No. 01.14.0231.00, under the Centro de Referencia em Radiocomunicacoes - CRR project of the Instituto Nacional de Telecomunicacoes (Inatel), Brazil.Silva, BM.; Rodrigues, JJPC.; Canelo, F.; Lopes, IMC.; Lloret, J. (2019). Towards a Cooperative Security System for Mobile-Health Applications. Electronic Commerce Research and Applications. 19(3):629-654. https://doi.org/10.1007/s10660-014-9154-362965419

Securing mobile ad hoc network routing protocols

Master'sMASTER OF ENGINEERIN

A New Visual Public-Key Cryptosystem Based On Non-Expansion Technique And Boolean Operations

Many public-key cryptosystems are used in our daily lives to attain privacy, authenticity, integrity and non-repudiation. However, most of the existing public-key algorithms are based on complex mathematical computations. Until recently, building a highly secured public-key cryptosystem without utilizing complex computations has been a serious challenge, making it necessary for investigations to develop new cryptography methods. Visual cryptography is special because the scheme requires visual inspection or the equivalence of simple Boolean computation and therefore, does not require complex computations. The basic design of visual cryptography exploits the human visual system, to recover secret images. Moreover, the visual inspection process could be carried out very easily by humans, but hard for the computer to imitate. Indirectly, such scheme adds extra protection to the visual scheme against brute-force search on the visual secret key