A Diffie-Hellman based key management scheme for hierarchical access control

All organizations share data in a carefully managed fashion\ud by using access control mechanisms. We focus on enforcing access control by encrypting the data and managing the encryption keys. We make the realistic assumption that the structure of any organization is a hierarchy of security classes. Data from a certain security class can only be accessed by another security class, if it is higher or at the same level in the hierarchy. Otherwise access is denied. Our solution is based on the Die-Hellman key exchange protocol. We show, that the theoretical worst case performance of our solution is slightly better than that of all other existing solutions. We also show, that our performance in practical cases is linear in the size of the hierarchy, whereas the best results from the literature are quadratic

An Identity-Based Group Signature with Membership Revocation in the Standard Model

Group signatures allow group members to sign an arbitrary number\ud of messages on behalf of the group without revealing their\ud identity. Under certain circumstances the group manager holding a\ud tracing key can reveal the identity of the signer from the\ud signature. Practical group signature schemes should support\ud membership revocation where the revoked member loses the\ud capability to sign a message on behalf of the group without\ud influencing the other non-revoked members. A model known as\ud \emph{verifier-local revocation} supports membership revocation.\ud In this model the trusted revocation authority sends revocation\ud messages to the verifiers and there is no need for the trusted\ud revocation authority to contact non-revoked members to update\ud their secret keys. Previous constructions of verifier-local\ud revocation group signature schemes either have a security proof in the\ud random oracle model or are non-identity based. A security proof\ud in the random oracle model is only a heuristic proof and\ud non-identity-based group signature suffer from standard Public Key\ud Infrastructure (PKI) problems, i.e. the group public key is not\ud derived from the group identity and therefore has to be certified.\ud \ud \ud In this work we construct the first verifier-local revocation group\ud signature scheme which is identity-based and which has a security proof in the standard model. In\ud particular, we give a formal security model for the proposed\ud scheme and prove that the scheme has the\ud property of selfless-anonymity under the decision Linear (DLIN)\ud assumption and it is fully-traceable under the\ud Computation Diffie-Hellman (CDH) assumption. The proposed scheme is based on prime order bilinear\ud groups

Dynamic User Role Assignment in Remote Access Control

The Role-Based Access Control (RBAC) model has been widely applied to a single domain in which users are known to the administrative unit of that domain, beforehand. However, the application of the conventional RBAC model for remote access control scenarios is not straightforward. In such scenarios, the access requestor is outside of the provider domain and thus, the user population is heterogeneous and dynamic. Here, the main challenge is to automatically assign users to appropriate roles of the provider domain. Trust management has been proposed as a supporting technique to solve the problem of remote access control. The key idea is to establish a mutual trust between the requestor and provider based on credentials they exchange. However, a credential doesn't convey any information about the behavior of its holder during the time it is being used. Furthermore, in terms of privileges granted to the requestor, existing trust management systems are either too restrictive or not restrictive enough. In this paper, we propose a new dynamic user-role assignment approach for remote access control, where a stranger requests for access from a provider domain. Our approach has two advantages compared to the existing dynamic user-role assignment techniques. Firstly, it addresses the principle of least privilege without degrading the efficiency of the access control system. Secondly, it takes into account both credentials and the past behavior of the requestor in such a way that he cannot compensate for the lack of necessary credentials by having a good past behavior

Public-Key Encryption with Delegated Search

In public-key setting, Alice encrypts email with public key of Bob, so that only Bob will be able to learn contents of email. Consider scenario when computer of Alice is infected and unbeknown to Alice it also embeds malware into message. Bob's company, Carol, cannot scan his email for malicious content as it is encrypted so burden is on Bob to do scan. This is not efficient. We construct mechanism that enables Bob to provide trapdoors to Carol such that Carol, given encrypted data and malware signature, is able to check whether encrypted data contains malware signature, without decrypting it. We refer to this mechanism as Public-Key Encryption with Delegated Search SPKE.\ud \ud We formalize SPKE and give construction based on ElGamal public-key encryption (PKE). proposed scheme has ciphertexts which are both searchable and decryptable. This property of scheme is crucial since entity can search entire content of message, in contrast to existing searchable public-key encryption schemes where search is done only in metadata part. We prove in standard model that scheme is ciphertext indistinguishable and trapdoor indistinguishable under Symmetric External Diffie-Hellman (sxdh) assumption. We prove also ciphertext one-wayness of scheme under modified Computational Diffie-Hellman (mcdh) assumption. We show that our PKEDS scheme can be used in different applications such as detecting encrypted malwares and forwarding encrypted emails

A Type-and-Identity-based Proxy Re-Encryption Scheme and its Application in Healthcare

Proxy re-encryption is a cryptographic primitive developed to delegate the decryption right from one party (the delegator) to another (the delegatee). In a proxy re-encryption scheme, the delegator assigns a key to a proxy to re-encrypt all messages encrypted with his public key such that the re-encrypted ciphertexts can be decrypted with the delegatee’s private key. We propose a type-and-identity-based proxy re-encryption scheme based on the Boneh-Franklin Identity Based Encryption (IBE) scheme. In our scheme, the delegator can categorize messages into different types and delegate the decryption right of each type to the delegatee through a proxy. Our scheme enables the delegator to provide the proxy fine-grained re-encryption capability. As an application, we propose a fine-grained Personal Health Record (PHR) disclosure scheme for healthcare service by applying the proposed scheme

Experimenting with linear search in encrypted data

Song, Wagner and Perrig have published a theoretical paper about keyword search on encrypted textual data. We describe a prototype implementing their theory. Tests are carried out with this prototype to analyse efficiency and timing aspects. As expected encryption and search times are linear in the size of the database. More interestingly they also depend on the parameters used in the protocol

LicenseScript: A Novel Digital Rights Language and its Semantics

We propose LicenseScript as a new multiset rewriting/ logic based language for expressing dynamic conditions of use of digital assets such as music, video or private data. LicenseScript differs from other DRM languages in that it caters for the intentional but legal manipulation of data. We believe this feature is the answer to providing the flexibility needed to support emerging usage paradigms of digital data. We provide the language with a simple semantics based on traces

SOFIR: Securely Outsourced Forensic Image Recognition

Forensic image recognition tools are used by law enforcement agencies all over the world to automatically detect illegal images on confiscated equipment. This detection is commonly done with the help of a strictly confidential database consisting of hash values of known illegal images. To detect and mitigate the distribution of illegal images, for instance in network traffic of companies or Internet service providers, it is desirable to outsource the recognition of illegal images to these companies. However, law enforcement agencies want to keep their hash databases secret at all costs as an unwanted release may result in misuse which could ultimately render these databases useless.\ud We present SOFIR, a tool for the Secure Outsourcing of Forensic Image Recognition allowing companies and law enforcement agencies to jointly detect illegal network traffic at its source, thus facilitating immediate regulatory actions. SOFIR cryptographically hides the hash database from the involved companies. At fixed intervals, SOFIR sends out an encrypted report to the law enforcement agency that only contains the number of found illegal images in the given interval, while otherwise keeping the company’s legal network traffic private. Our experimental results show the effectiveness and practicality of our approach in the real-world

Simultaneous capture of the color and topography of paintings using fringe encoded stereo vision

Introduction: Paintings are versatile near-planar objects with material characteristics that vary widely. The fact that paint has a material presence is often overlooked, mostly due to the fact that we encounter many of these artworks through two dimensional reproductions. The capture of paintings in the third dimension is not only interesting for study, restoration and conservation, but it also facilitates making three dimensional reproductions through novel 3-D printing methods. No single imaging method is ideally suited to capture the painting’s color and topography and each of them have specific drawbacks. We have therefore designed an efficient hybrid imaging system dedicated to capturing paintings in both color and topography with a high resolution. Results: A hybrid solution between fringe projection and stereo imaging is proposed involving two cameras and a projector. Fringe projection is aided by sparse stereo matching to serve as an image encoder. These encoded images processed by the stereo cameras then help solve the correspondence problem in stereo matching, leading to a dense and accurate topographical map, while simultaneously capturing its color. Through high-end cameras, special lenses and filters we capture a surface area of 170 square centimeter with an in-plane effective resolution of 50 micron and a depth precision of 9 micron. Semi-automated positioning of the system and data stitching consequently allows for the capture of larger surfaces. The capture of the 2 square meter big Jewish Bride by Rembrandt yielded 1 billion 3-D points. Conclusion: The reproductive properties of the imaging system are conform the digitization guidelines for cultural heritage. The data has enabled us to make high resolution 3-D prints of the works by Rembrandt and Van Gogh we have captured, and confirms that the system performs well in capturing both the color and depth information.Chemical EngineeringMechanical, Maritime and Materials Engineerin

Privacy Enhanced Access Control by Means of Policy Blinding

Traditional techniques of enforcing an access control policy\ud rely on an honest reference monitor to enforce the policy. However, for\ud applications where the resources are sensitive, the access control policy\ud might also be sensitive. As a result, an honest-but-curious reference monitor would glean some interesting information from the requests that it\ud processes. For example if a requestor in a role psychiatrist is granted access to a document, the patient associated with that document probably\ud has a psychiatric problem. The patient would consider this sensitive in-\ud formation, and she might prefer the honest-but-curious reference monitor\ud to remain oblivious of her mental problem.\ud We present a high level framework for querying and enforcing a role\ud based access control policy that identifies where sensitive information\ud might be disclosed. We then propose a construction which enforces a\ud role based access control policy cryptographically, in such a way that the\ud reference monitor learns as little as possible about the policy. (The reference monitor only learns something from repeated queries). We prove\ud the security of our scheme showing that it works in theory, but that it\ud has a practical drawback. However, the practical drawback is common\ud to all cryptographically enforced access policy schemes. We identify several approaches to mitigate the drawback and conclude by arguing that\ud there is an underlying fundamental problem that cannot be solved. We\ud also show why attribute based encryption techniques do not not solve the\ud problem of enforcing policy by an honest but curious reference monitor