Separable and anonymous identity-based key issuing

In identity-based (ID-based) cryptosystems, a local registration authority (LRA) is responsible for authentication of users while the key generation center (KGC) is responsible for computing and sending the private keys to users and therefore, a secure channel is required. For privacy-oriented applications, it is important to keep in secret whether the private key corresponding to a certain identity has been requested. All of the existing ID-based key issuing schemes have not addressed this anonymity issue. Besides, the separation of duties of LRA and KGC has not been discussed as well. We propose a novel separable and anonymous ID-based key issuing scheme without secure channel. Our protocol supports the separation of duties between LRA and KGC. The private key computed by the KGC can be sent to the user in an encrypted form such that only the legitimate key requester authenticated by LRA can decrypt it, and any eavesdropper cannot know the identity corresponding to the secret key. © 2005 IEEE.published_or_final_versio

Privacy Enhancing Protocols using Pairing Based Cryptography

This thesis presents privacy enhanced cryptographic constructions, consisting of formal definitions, algorithms and motivating applications. The contributions are a step towards the development of cryptosystems which, from the design phase, incorporate privacy as a primary goal. Privacy offers a form of protection over personal and other sensitive data to individuals, and has been the subject of much study in recent years. Our constructions are based on a special type of algebraic group called bilinear groups. We present existing cryptographic constructions which use bilinear pairings, namely Identity-Based Encryption (IBE). We define a desirable property of digital signatures, blindness, and present new IBE constructions which incorporate this property. Blindness is a desirable feature from a privacy perspective as it allows an individual to obscure elements such as personal details in the data it presents to a third party. In IBE, blinding focuses on obscuring elements of the identity string which an individual presents to the key generation centre. This protects an individual's privacy in a direct manner by allowing her to blind sensitive elements of the identity string and also prevents a key generation centre from subsequently producing decryption keys using her full identity string. Using blinding techniques, the key generation centre does not learn the full identity string. In this thesis, we study selected provably-secure cryptographic constructions. Our contribution is to reconsider the design of such constructions with a view to incorporating privacy. We present the new, privacy-enhanced cryptographic protocols using these constructions as primitives. We refine useful existing security notions and present feasible security definitions and proofs for these constructions

Blacklistable Anonymous Credentials: Blocking Misbehaving Users without TTPs (Extended Version)

Several credential systems have been proposed in which users can authenticate to services anonymously. Since anonymity can give users the license to misbehave, some variants allow the selective deanonymization (or linking) of misbehaving users upon a complaint to a trusted third party (TTP). The ability of the TTP to revoke a user\u27s privacy at any time, however, is too strong a punishment for misbehavior. To limit the scope of deanonymization, systems such as ``e-cash\u27\u27 have been proposed in which users are deanonymized under only certain types of well-defined misbehavior such as ``double spending.\u27\u27 While useful in some applications, it is not possible to generalize such techniques to more subjective definitions of misbehavior. We present the first anonymous credential system in which services can ``blacklist\u27\u27 misbehaving users without contacting a TTP. Since blacklisted users remain anonymous, misbehaviors can be judged subjectively without users fearing arbitrary deanonymization by a TTP

Cryptography in privacy-preserving applications.

Tsang Pak Kong.Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.Includes bibliographical references (leaves 95-107).Abstracts in English and Chinese.Abstract --- p.iiAcknowledgement --- p.ivChapter 1 --- Introduction --- p.1Chapter 1.1 --- Privacy --- p.1Chapter 1.2 --- Cryptography --- p.5Chapter 1.2.1 --- History of Cryptography --- p.5Chapter 1.2.2 --- Cryptography Today --- p.6Chapter 1.2.3 --- Cryptography For Privacy --- p.7Chapter 1.3 --- Thesis Organization --- p.8Chapter 2 --- Background --- p.10Chapter 2.1 --- Notations --- p.10Chapter 2.2 --- Complexity Theory --- p.11Chapter 2.2.1 --- Order Notation --- p.11Chapter 2.2.2 --- Algorithms and Protocols --- p.11Chapter 2.2.3 --- Relations and Languages --- p.13Chapter 2.3 --- Algebra and Number Theory --- p.14Chapter 2.3.1 --- Groups --- p.14Chapter 2.3.2 --- Intractable Problems --- p.16Chapter 2.4 --- Cryptographic Primitives --- p.18Chapter 2.4.1 --- Public-Key Encryption --- p.18Chapter 2.4.2 --- Identification Protocols --- p.21Chapter 2.4.3 --- Digital Signatures --- p.22Chapter 2.4.4 --- Hash Functions --- p.24Chapter 2.4.5 --- Zero-Knowledge Proof of Knowledge --- p.26Chapter 2.4.6 --- Accumulators --- p.32Chapter 2.4.7 --- Public Key Infrastructure --- p.34Chapter 2.5 --- Zero Knowledge Proof of Knowledge Protocols in Groups of Unknown Order --- p.36Chapter 2.5.1 --- The Algebraic Setting --- p.36Chapter 2.5.2 --- Proving the Knowledge of Several Discrete Logarithms . --- p.37Chapter 2.5.3 --- Proving the Knowledge of a Representation --- p.38Chapter 2.5.4 --- Proving the Knowledge of d Out of n Equalities of Discrete Logarithms --- p.39Chapter 2.6 --- Conclusion --- p.42Chapter 3 --- Related Works --- p.43Chapter 3.1 --- Introduction --- p.43Chapter 3.2 --- Group-Oriented Signatures without Spontaneity and/or Anonymity --- p.44Chapter 3.3 --- SAG Signatures --- p.46Chapter 3.4 --- Conclusion --- p.49Chapter 4 --- Linkable Ring Signatures --- p.50Chapter 4.1 --- Introduction --- p.50Chapter 4.2 --- New Notions --- p.52Chapter 4.2.1 --- Accusatory Linking --- p.52Chapter 4.2.2 --- Non-slanderability --- p.53Chapter 4.2.3 --- Linkability in Threshold Ring Signatures --- p.54Chapter 4.2.4 --- Event-Oriented Linking --- p.55Chapter 4.3 --- Security Model --- p.56Chapter 4.3.1 --- Syntax --- p.56Chapter 4.3.2 --- Notions of Security --- p.58Chapter 4.4 --- Conclusion --- p.63Chapter 5 --- Short Linkable Ring Signatures --- p.64Chapter 5.1 --- Introduction --- p.64Chapter 5.2 --- The Construction --- p.65Chapter 5.3 --- Security Analysis --- p.68Chapter 5.3.1 --- Security Theorems --- p.68Chapter 5.3.2 --- Proofs --- p.68Chapter 5.4 --- Discussion --- p.70Chapter 5.5 --- Conclusion --- p.71Chapter 6 --- Separable Linkable Threshold Ring Signatures --- p.72Chapter 6.1 --- Introduction --- p.72Chapter 6.2 --- The Construction --- p.74Chapter 6.3 --- Security Analysis --- p.76Chapter 6.3.1 --- Security Theorems --- p.76Chapter 6.3.2 --- Proofs --- p.77Chapter 6.4 --- Discussion --- p.79Chapter 6.5 --- Conclusion --- p.80Chapter 7 --- Applications --- p.82Chapter 7.1 --- Offline Anonymous Electronic Cash --- p.83Chapter 7.1.1 --- Introduction --- p.83Chapter 7.1.2 --- Construction --- p.84Chapter 7.2 --- Electronic Voting --- p.85Chapter 7.2.1 --- Introduction --- p.85Chapter 7.2.2 --- Construction . --- p.87Chapter 7.2.3 --- Discussions --- p.88Chapter 7.3 --- Anonymous Attestation --- p.89Chapter 7.3.1 --- Introduction --- p.89Chapter 7.3.2 --- Construction --- p.90Chapter 7.4 --- Conclusion --- p.91Chapter 8 --- Conclusion --- p.92A Paper Derivation --- p.94Bibliography --- p.9

Liquidity Traps: How to Avoid Them and How to Escape Them

The paper considers ways of avoiding a liquidity trap and ways of getting out of one. Unless lower short nominal interest rates are associated with significantly lower interest volatility, a lower average rate of inflation, which will be associated with lower expected nominal interest rates, increases the odds that the zero nominal interest rate floor will become a binding constraint. The empirical evidence on this issue is mixed. Once in a liquidity trap, there are two means of escape. The first is to use expansionary fiscal policy. The second is to lower the zero nominal interest rate floor. This second option involves paying negative interest on government 'bearer bonds' -- coin and currency, that is 'taxing money', as advocated by Gesell. This would also reduce the likelihood of ending up in a liquidity trap. Taxing currency amounts to having periodic 'currency reforms', that is, compulsory conversions of 'old' currency into 'new' currency, say by stamping currency. The terms of the conversion can be set to achieve any positive or negative interest rate on currency. There are likely to be significant shoe leather costs associated with such schemes. The policy question then becomes how much shoe leather it takes to fill an output gap? Finally the paper develops a simple analytical model showing how the economy can get into a liquidity trap and how Gesell money is one way of avoiding it or escaping from it.

Databases, Doctrine, and Constitutional Criminal Procedure

Over the past twenty years there has been an explosion in the creation, availability, and use of criminal justice databases. Large scale database systems now routinely influence law enforcement decisions ranging from formal determinations to arrest or convict an individual to informal judgments to subject a person to secondary pre-flight screening or investigate possible gang membership. Evidence gathered from database-related sources is now commonly introduced, and can play a pivotal proof role, in criminal trials. Although much has been written about the failure of constitutional law to adequately respond to the threat to privacy rights posed by databases, less attention has focused upon the awkward fit between database-generated evidence and the conventional modes of analysis in constitutional criminal procedure. This Essay examines databases as a tool of law enforcement and sets forth tentative steps toward a theory of constitutional violations in this area

Multi-way Cloud-Side Access Control for Encrypted Cloud Storage

Individuals support the incredible intensity of cloud computing, however can't completely believe the cloud providers to have protection delicate data, because of the nonattendance of client to-cloud controllability. To guarantee confidentiality, data administrators redistribute scrambled data rather than plaintexts. To impart the scrambled files to different clients, ciphertext-strategy attribute-based encryption can be used to direct fine-grained and administrator driven access control. Yet, this doesn't adequately get secure against different assaults. Numerous past schemes didn't concede the cloud supplier the capacity to check whether a downloader can decode. Along these lines, these files ought to be accessible to everybody open to the cloud storage. A noxious aggressor can download a great many files to dispatch monetary refusal of supportability assaults, which will to a great extent expend the cloud asset. The payer of the cloud service bears the cost. These worries ought to be settled in true open cloud storage. In this paper, we propose an answer for secure encoded cloud storages from EDoS assaults and give asset utilization responsibility. We present two conventions for various settings, trailed by execution and security examination. Furthermore, attribute-based control in the framework additionally empowers the cloud server to confine the entrance to those clients with a similar arrangement of attributes while protecting client security, i.e., the cloud server just realizes that the client satisfies the necessary predicate, however has no clue on the specific identity of the client