In this paper, we define and explore proofs of retrievability (PORs). A POR scheme enables an archive or back-up service (prover) to produce a concise proof that a user (verifier) can retrieve a target file F, that is, that the archive retains and reliably transmits file data sufficient for the user to recover F in its entirety.A POR may be viewed as a kind of cryptographic proof of knowledge (POK), but one specially designed to handle a large file (or bitstring) F. We explore POR protocols here in which the communication costs, number of memory accesses for the prover, and storage requirements of the user (verifier) are small parameters essentially independent of the length of F. In addition to proposing new, practical POR constructions, we explore implementation considerations and optimizations that bear on previously explored, related schemes.In a POR, unlike a POK, neither the prover nor the verifier need actually have knowledge of F. PORs give rise to a new and unusual security definition whose formulation is another contribution of our work.We view PORs as an important tool for semi-trusted online archives. Existing cryptographic techniques help users ensure the privacy and integrity of files they retrieve. It is also natural, however, for users to want to verify that archives do not delete or modify files prior to retrieval. The goal of a POR is to accomplish these checks without users having to download the files themselves. A POR can also provide quality-of-service guarantees, i.e., show that a file is retrievable within a certain time bound.

PORs: Proofs of Retrievability for Large Files

We construct two efficient Identity-Based Encryption (IBE) systems that admit selective-identity security reductions without random oracles in groups equipped with a bilinear map. Selective-identity secure IBE is a slightly weaker security model than the standard security model for IBE. In this model the adversary must commit ahead of time to the identity that it intends to attack, whereas in an adaptive-identity attack the adversary is allowed to choose this identity adaptively. Our first system—BB1—is based on the well studied decisional bilinear Diffie–Hellman assumption, and extends naturally to systems with hierarchical identities, or HIBE. Our second system—BB2—is based on a stronger assumption which we call the Bilinear Diffie–Hellman Inversion assumption and provides another approach to building IBE systems.

Our first system, BB1, is very versatile and well suited for practical applications: the basic hierarchical construction can be efficiently secured against chosen-ciphertext attacks, and further extended to support efficient non-interactive threshold decryption, among others, all without using random oracles. Both systems, BB1 and BB2, can be modified generically to provide “full” IBE security (i.e., against adaptive-identity attacks), either using random oracles, or in the standard model at the expense of a non-polynomial but easy-to-compensate security reduction.

Efficient selective identity-based encryption without random oracles

Overview of the combination of biometric matchers

In this paper, we consider a new class of unconditionally secure authentication codes, called linear authentication codes (or linear A-codes). We show that a linear A-code can be characterized by a family of subspaces of a vector space over a finite field. We then derive an upper bound on the size of the source space when other parameters of the system, that is, the sizes of the key space and the authenticator space, and the deception probability, are fixed. We give constructions that are asymptotically close to the bound and show applications of these codes in constructing distributed authentication systems.

Linear authentication codes: bounds and constructions

Passports are documents that help immigration officers to identify people. In order to strongly authenticate their data and to automatically identify people, they are now equipped with RFID chips. These contain private information, biometrics, and a digital signature by issuing authorities. Although they substantially increase security at the border controls, they also come with new security and privacy issues. In this paper, we survey existing protocols and their weaknesses.

/pdf/about-machine-readable-travel-documents-4yas77o82e.pdf

About Machine-Readable Travel Documents

Biometric cryptosystems provide an innovative solution for cryptographic key generation, encryption as well as biometric template protection. Besides high authentication accuracy, a good biometric cryptosystem is expected to protect biometric templates effectively, which requires that helper data does not reveal significant information about the templates. Previous works predominantly follow an appropriate entropy definition to measure the security of biometric cryptosystems. In this paper, we point out limitations of entropy-based security analysis and propose a new security analysis framework that combines information-theoretic approach with computational security. In addition, we construct a fingerprint-based multibiometric cryptosystem (MBC) using decision level fusion. Hash functions are employed in our construction to further protect each single biometric trait. The experimental results and security analysis demonstrate that the proposed MBC provides stronger security and better authentication accuracy compared with a cryptosystem based on single biometric.

A new biocryptosystem-oriented security analysis framework and implementation of multibiometric cryptosystems based on decision level fusion

Certificateless Public-key Authenticated Encryption with Keyword Search (CLPAEKS) is derived from the Public-key Authenticated Encryption with Keyword Search (PAEKS) and simultaneously combines the features of the Public Key Cryptography (CLPKC). In a CLPAEKS scheme, the ciphertext is designed to meet the need for both confidentiality and authentication, i.e., on one hand, the ciphertext is the encryption of the keyword; on the other hand, adversaries are incapable of generating a valid ciphertext without the owner’s private key. He et al. formalized security models for CLPAEKS and proposed a CLPAEKS scheme. However, we find their models are incomplete to capture the security requirements for CLPAEKS and re-formalize the security requirements for CLPAEKS in terms of trapdoor privacy and ciphertext indistinguishability. Besides, we point out that their scheme is vulnerable to the Keyword Guessing Attack (KGA) by a malicious receiver, which is not considered in their security model. Then we modify He et al.’s scheme and prove that the new scheme meets the new security requirements.

Towards Enhanced Security for Certificateless Public-Key Authenticated Encryption with Keyword Search

The Advanced Encryption Standard (AES) is the most widely used symmetric encryption algorithm. Its security is mainly based on the structure of the S-box. In this paper, we present a new way to create S-boxes for AES and exhibit an S-box with improved cryptographic properties such as Bit Independence Criterion (BIC), periodicity, algebraic complexity, Strict Avalanche Criterion (SAC) and Distance to SAC.

A New Improved AES S-box with Enhanced Properties

Cloud auditing with ownership transfer is a provable data possession scheme meeting verifiability and transferability simultaneously. In particular, not only cloud data can be transferred to other cloud clients, but also tags for integrity verification can be transferred to new data owners. More concretely, it requires that tags belonging to the old owner can be transformed into that of the new owner by replacing the secret key for tag generation while verifiability still remains. We found that existing solutions are less efficient due to the huge communication overhead linear with the number of tags. In this paper, we propose a secure auditing protocol with efficient ownership transfer for cloud data. Specifically, we sharply reduce the communication overhead produced by ownership transfer to be independent of the number of tags, making it with a constant size. Meanwhile, the computational cost during this process on both transfer parties is constant as well.

Secure Cloud Auditing with Efficient Ownership Transfer

This work envisions a new encryption primitive for many-to-many paradigms such as group messaging systems. Previously, puncturable encryption (PE) was introduced to provide forward security for asynchronous messaging services. However, existing PE schemes were proposed only for one-to-one communication, and causes a significant overhead for a group messaging system. In fact, the group communication over PE can only be achieved by encrypting a message multiple times for each receiver by the sender’s device, which is usually suitable to restricted resources such as mobile phones or sensor devices. Our new suggested scheme enables to re-encrypt ciphertexts of puncturable encryption by a message server (i.e., a proxy) so that computationally heavy operations are delegated to the server who has more powerful processors and a constant power source. We then proposed a new Puncturable Proxy Re-Encryption (PPRE) scheme. The scheme is inspired by unidirectional proxy re-encryption (UPRE), which achieves forward secrecy through fine-grained revocation of decryption capability by integrating the PE scheme. This paper first presents a forward secure PPRE in the group messaging service. Our scheme is IND-CCA secure under 3-weak Decision Bilinear Diffie-Hellman Inversion assumption.

Puncturable Proxy Re-Encryption Supporting to Group Messaging Service

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