A second generation of nonrepudiation protocols

A non-repudiation protocol from party S to party R performs two tasks. First, the protocol enables party S to send to party R some text x along with sufficient evidence (that can convince a judge) that x was indeed sent by S. Second, the protocol enables party R to receive text x from S and to send to S sufficient evidence (that can convince a judge) that x was indeed received by R. The first generation of non-repudiation protocols were published in the period 1996-2000. In this dissertation, we design a second generation of non-repudiation protocols that enjoy several interesting properties. First, we identify in this dissertation a special class of non-repudiation protocols, called two-phase protocols. The two parties, S and R, in each two-phase protocol execute the protocol as specified until one of the two parties receives its needed proof. Then and only then does this party refrain from sending any more message specified by the protocol because these messages only help the other party complete its proof. We show that the execution of each two-phase protocol is deterministic and does not require synchronized real-time clocks. We also show that each two-phase protocol needs to involve a trusted third party T beside the two original parties, S and R. Second, we show that if party R in a two-phase protocol has a real-time clock and knows an upper bound on the round trip delay from R to S and back to R, then the two-phase protocol does not need to involve a trusted third party T. Third, we design a non-repudiation protocol for transferring file F from a sender S to a receiver R over a cloud C. This protocol is designed such that there is no direct communication between parties S and R. Rather all communications between S and R are carried out through cloud C. In this protocol parties S and R do not need to store a local copy of file F and the proofs that are needed by the two parties S and R (the only copy of file F and the proofs is stored in cloud C). Fourth, we design a new non-repudiation protocol from S to R over C where some of the proofs stored in cloud C get lost. This new protocol has an interesting stabilization property which ensures that when some of the proofs get lost, and one party can get the needed proofs but the other party cannot get its needed proofs from cloud C, then eventually, neither party is able to receive its needed proofs from cloud C. Fifth, we design a non-repudiation protocol for transferring files from a sender S to a subset of potential receivers {R.1, R.2, ..., R.n} over a cloud C. The protocol guarantees that after each file F is transferred from sender S to a subset of the potential receivers, then (1) each receiver R.i in the subset ends up with a proof that file F was indeed sent by sender S to R.i, and (2) sender S ends up with a proof that file F was indeed received from S by each receiver R.i in the subset.Computer Science

AES (Advanced Encryption Standard) and RSA (Rivest–Shamir–Adleman) Encryption on Digital Signature Document: A Literature Review

Distributed digital documents, it can utilize cryptographic methods to provide confidentiality, data integrity, authentication and non repudiation services. Watermark in this case serves as authentic proof of ownership of the data or document, and its existence should not damage or change the contents or counter of digital data or digital documents. The RSA and AES encryption methods in digital signatures are appropriate to be taken as a reliable method. But a unique biometric key idea emerged, one of which was used to authenticate users

Cryptanalysis of the RSA-CEGD protocol

Recently, Nenadi\'c et al. (2004) proposed the RSA-CEGD protocol for certified delivery of e-goods. This is a relatively complex scheme based on verifiable and recoverable encrypted signatures (VRES) to guarantee properties such as strong fairness and non-repudiation, among others. In this paper, we demonstrate how this protocol cannot achieve fairness by presenting a severe attack and also pointing out some other weaknesses.Comment: 8 pages, 1 figur

An assessment of blockchain consensus protocols for the Internet of Things

In a few short years the Internet of Things has become an intrinsic part of everyday life, with connected devices included in products created for homes, cars and even medical equipment. But its rapid growth has created several security problems, with respect to the transmission and storage of vast amounts of customers data, across an insecure heterogeneous collection of networks. The Internet of Things is therefore creating a unique set of risk and problems that will affect most households. From breaches in confidentiality, which could allow users to be snooped on, through to failures in integrity, which could lead to consumer data being compromised; devices are presenting many security challenges to which consumers are ill equipped to protect themselves from. Moreover, when this is coupled with the heterogeneous nature of the industry, and the interoperable and scalability problems it becomes apparent that the Internet of Things has created an increased attack surface from which security vulnerabilities may be easily exploited. However, it has been conjectured that blockchain may provide a solution to the Internet of Things security and scalability problems. Because of blockchain’s immutability, integrity and scalability, it is possible that its architecture could be used for the storage and transfer of Internet of Things data. Within this paper a cross section of blockchain consensus protocols have been assessed against a requirement framework, to establish each consensus protocols strengths and weaknesses with respect to their potential implementation in an Internet of Things blockchain environment

External Debt, Capital Flight and Political Risk

This paper provides an explanation of the simultaneous occurrence of large accumulation of external debt, private capital outflow and relatively low domestic capital formation in developing countries. We consider a general equilibrium model in which two types of government with conflicting distributional goals randomly alternate in office. Uncertainty over the fiscal policies of future governments generates private capital flight and small domestic investment. This political uncertainty also provides the incentives for the current government to over accumulate external debt. The model also predicts that left wing governments are more inclined to impose restrictions on capital outflows than right wing governments. Finally, we examine how political uncertainty affects the risk premium charged by lenders and how debt repudiation may occur after a change of political regime.

Efficient Construction of Nominative Signature Secure under Symmetric Key Primitives and Standard Assumptions on Lattice

Nominative signature is a cryptographic primitive where two parties collude to produce a signature. It is a user certification system and has applications in variety of sectors where nominee cannot trust heavily on the nominator to validate nominee’s certificate and only targeted entities are allowed to verify signature on sensitive data. We provide a new construction for nominative signature from standard assumptions on lattice. Our construction relies on collision resistant preimage sampleable function and symmetric key primitives like collision resistant pseudorandom function and zero knowledge proof system ZKB++ for Boolean circuits. We provide a detailed security analysis and show that our construction achieves security under unforgeability, invisibility, impersonation and non-repudiation in existing model. Furthermore, our construction exhibits non-transferability. The security under non-repudiation is achieved in the quantum random oracle model using Unruh transform to ZKB++