Ciphertext Size Research Articles

Efficient attribute-based data sharing in mobile clouds

Ciphertext-policy attribute-based encryption (CP-ABE) is extremely suitable for cloud computing environment in that it enables data owners to make and enforce access policies themselves. However, most of existing CP-ABE schemes suffer severe efficiency drawbacks due to large ciphertext size and computation cost, and hence are not suitable for mobile clouds, where users are usually resource-limited. In this paper, we first present a generic attribute-based data sharing system based on a hybrid mechanism of CP-ABE and a symmetric encryption scheme. Then, we propose a CP-ABE scheme which features constant computation cost and constant-size ciphertexts. The proposed CP-ABE scheme is proven selective-secure in the random oracle model under the decision n-BDHE assumption, where n represents the total number of attributes in universe. It can efficiently support AND-gate access policies with multiple attribute values and wildcards. Theoretical analysis and experimental results indicate that the proposed scheme is extremely suitable for data sharing in mobile clouds.

Substring-Searchable Symmetric Encryption

Abstract In this paper, we consider a setting where a client wants to outsource storage of a large amount of private data and then perform substring search queries on the data – given a data string s and a search string p, find all occurrences of p as a substring of s. First, we formalize an encryption paradigm that we call queryable encryption, which generalizes searchable symmetric encryption (SSE) and structured encryption. Then, we construct a queryable encryption scheme for substring queries. Our construction uses suffix trees and achieves asymptotic efficiency comparable to that of unencrypted suffix trees. Encryption of a string of length n takes O(λn) time and produces a ciphertext of size O(λn), and querying for a substring of length m that occurs k times takes O(λm+k) time and three rounds of communication. Our security definition guarantees correctness of query results and privacy of data and queries against a malicious adversary. Following the line of work started by Curtmola et al. (ACM CCS 2006), in order to construct more efficient schemes we allow the query protocol to leak some limited information that is captured precisely in the definition. We prove security of our substring-searchable encryption scheme against malicious adversaries, where the query protocol leaks limited information about memory access patterns through the suffix tree of the encrypted string.

Efficient attribute-based signature and signcryption realizing expressive access structures

This paper addresses the open problem of designing attribute-based signature (ABS) schemes with constant number of bilinear pairing operations for signature verification or short signatures for more general policies posed by Gagne et al. in Pairing 2012. Designing constant-size ABS for expressive access structures is a challenging task. We design two key-policy ABS schemes with constant-size signature for expressive linear secret-sharing scheme (LSSS)-realizable monotone access structures. Both the schemes utilize only 3 pairing operations in signature verification process. The first scheme is small universe construction, while the second scheme supports large universes of attributes. The signing key is computed according to LSSS-realizable access structure over signer's attributes, and the message is signed with an attribute set satisfying the access structure. Our ABS schemes provide the existential unforgeability in selective attribute set security model and preserve signer privacy. We also propose a new attribute-based signcryption (ABSC) scheme for LSSS-realizable access structures utilizing only 6 pairings and making the ciphertext size constant. Our scheme is significantly more efficient than existing ABSC schemes. While the secret key (signing key or decryption key) size increases by a factor of number of attributes used in the system, the number of pairing evaluations is reduced to constant. Our protocol achieves (a) ciphertext indistinguishability under adaptive chosen ciphertext attacks assuming the hardness of decisional Bilinear Diffie---Hellman Exponent problem and (b) existential unforgeability under adaptive chosen message attack assuming the hardness of computational Diffie---Hellman Exponent problem. The security proofs are in selective attribute set security model without using any random oracle heuristic. In addition, our ABSC achieves public verifiability of the ciphertext, enabling any party to verify the integrity and validity of the ciphertext.

Adaptively secure broadcast encryption under standard assumptions with better efficiency

In this study, the authors present an efficient public-key broadcast encryption (PKBE) scheme with sub-linear size of public keys, private keys and ciphertexts and prove its adaptive security under standard assumptions. Compared with the currently best scheme of Garg et al. (CCS 2010) that provides adaptive security under standard assumptions and sub-linear size of various parameters, the ciphertext size of the author's scheme is 94% shorter and the encryption algorithm of their scheme is also 2.8 times faster than the scheme of Garg et al. To achieve their scheme, they adapt the dual system encryption technique of Waters. However, there is a challenging problem to use this technique for the construction of PKBE with sub-linear size of ciphertexts such as a tag compression problem. To overcome this problem, they first devise a novel tag update technique for broadcast encryption. Using this technique, they build an efficient PKBE scheme in symmetric bilinear groups, and prove its adaptive security under standard assumptions.

A Novel Constant size Cipher-text Scheme for Security in Real-time Systems

In this paper, we consider ‘secure attribute based system with short ciphertext’ is a tool for implementing fine-grained access control over encrypted data, and is conceptually similar to traditional access control methods such as Role-Based Access Control. However, current ‘secure attribute based system with short ciphertext’ schemes suffer from the issue of having long decryption keys, in which the size is linear to and dependent on the number of attributes.Ciphertext-Policy ABE (CP-ABE) provides a scalable way of encrypting data such that the encryptor defines the attribute set that the decryptor needs to possess in order to decrypt the ciphertext. We propose a novel ‘secure attribute based system with short ciphertext’ scheme with constantsize decryption keys independent of the number of attributes. We found that the size can be as small as 672 bits.

SECURED ARCHITECTURE FOR MULTI-CLOUD USING KEY AGGREGATION TECHNIQUE

Data storage and data sharing is the most important aspect in cloud computing, so sharing data and storing it in a secure way is the biggest task when adopting cloud services. In this paper, we will discuss how to share and store data effectively which will prevent the third party to access the secure data in cloud storage. This article provides a survey of using multiple clouds to achieve a security. In this we are introducing a public-key encryption known as Key-aggregate Cryptosystem (KAC). Cryptography is a technique which encodes a data using some key and produces unreadable data so that only a desired party is able to decode that data. KAC produces a constant size ciphertexts (unreadable data) such that decryption right for any set of ciphertexts are possible, means one can aggregate any set of secret keys and make them as compact as single key, but encompassing the power of all the keys being aggregate. This aggregate key is sent to other via secure channel (or via email) for decrypting the ciphertext set and remaining files outside the set are remains secret.

Patient Controlled Encryption using Key Aggregation

Cloud has become very important in internet world. Cloud provides storages, platforms which improves the functionality. Cloud storage shows how securely and flexibly we can store and share our data. This technique introduces a special type of encryption called as key-aggregate cryptosystem which allows user to share their data partially across cloud and which produces constant size ciphertext. In this technique user provide a constant-size aggregate key for different ciphertext classes in cloud storage, but the other encrypted files outside the class remain confidential. We also compare this technique with existing one. We implemented this cryptosystem for public-key patient-controlled encryption system.

Generalized closest substring encryption

We propose a new cryptographic notion called generalized closest substring encryption. In this notion, a ciphertext encrypted with a string \(S\) can be decrypted with a private key of another string \(S'\), if there exist a substring of \(S\), i.e. \(\hat{S}\), and a substring of \(S'\), i.e. \(\hat{S}'\), that are “close” to each other measured by their “overlap distance”. The overlap distance between \(\hat{S}\) and \(\hat{S}'\) is the number of identical positions at which the corresponding symbols are the same. In comparison with other encryption systems, the closest notion is the Fuzzy-IBE proposed by Sahai and Waters. The main difference is that the Fuzzy-IBE measures the overlap distance between \(S\) and \(S'\), while ours measures the overlap distance of all of their substrings (including the complete string), and we take the maximum value among those. The overlap distance between their substrings will measure the similarity of \(S\) and \(S'\) more precisely compared to the overlap distance between the two complete strings. We note that embedding this overlap distance in an encryption is a challenging task, in particular in order to achieve a practical scheme. Therefore, we invent a new approach to develop a practical generalized closest substring encryption system. The novelty of our approach relies on the way we generate ciphertext and private key representing the complete string so that they can still measure the overlap distance of substrings. The size of ciphertext and private key grow linearly only in the length of the input string. We prove the security in the selective model under a generalization of decision \(q\)-Bilinear Diffie–Hellman Exponent assumption.

CRT-based fully homomorphic encryption over the integers

In 1978, Rivest, Adleman and Dertouzos introduced the basic concept of privacy homomorphism that allows computation on encrypted data without decryption. It was an interesting work whose idea precedes the recent development of fully homomorphic encryption, although actual example schemes proposed in the paper are all susceptible to simple known-plaintext attacks.In this paper, we revisit one of their proposals, in particular the third scheme which is based on the Chinese Remainder Theorem and is ring homomorphic. It is known that only a single pair of known plaintext/ciphertext is needed to break this scheme. However, by exploiting the standard technique to insert an error to a message before encryption, we can cope with this problem. We present a secure modification of their proposal by showing that the proposed scheme is fully homomorphic and secure against the chosen plaintext attacks under the approximate GCD assumption and the sparse subset sum assumption when the message space is restricted to Z2k.Interestingly, the proposed scheme can be regarded as a generalization of the DGHV scheme with larger plaintext space. Our scheme has O∼(λ5) ciphertext expansion overhead while the DGHV has O∼(λ8) for the security parameter λ. When restricted to the homomorphic encryption scheme with depth of O(logλ), the overhead is reduced to O∼(λ). Our scheme can be used in applications requiring a large message space ZQ for logQ=O(λ4), or SIMD style operations on ZQk for logQ=O(λ),k=O(λ3), with O∼(λ5) ciphertext size as in the DGHV.

MDS Algorithm for Encryption

Most of the encryption algorithms used today generates huge cipher messages as well as long encryption keys. These approaches require time and are computationally intensive .While sending data packets through the network a compression technique along with cryptography can be applied to reduce the data packet size for better bandwidth utilization and hence faster transmission of data. In this study we propose a new encryption technique which will encrypt data into reduced size cipher text while keeping the check on size of key. The algorithm was first introduced in an earlier paper. In this study we modified algorithm to preprocess text as well as numeric data.

An efficient and provable secure revocable identity-based encryption scheme.

Revocation functionality is necessary and crucial to identity-based cryptosystems. Revocable identity-based encryption (RIBE) has attracted a lot of attention in recent years, many RIBE schemes have been proposed in the literature but shown to be either insecure or inefficient. In this paper, we propose a new scalable RIBE scheme with decryption key exposure resilience by combining Lewko and Waters’ identity-based encryption scheme and complete subtree method, and prove our RIBE scheme to be semantically secure using dual system encryption methodology. Compared to existing scalable and semantically secure RIBE schemes, our proposed RIBE scheme is more efficient in term of ciphertext size, public parameters size and decryption cost at price of a little looser security reduction. To the best of our knowledge, this is the first construction of scalable and semantically secure RIBE scheme with constant size public system parameters.

Practical key‐dependent message chosen‐ciphertext security based on decisional composite residuosity and quadratic residuosity assumptions

AbstractAn encryption scheme is key‐dependent message chosen plaintext attack (KDM‐CPA) secure if it is secure even against an attacker who has access to encryptions of messages that depend on the secret key. Such situations naturally occur in some scenarios such as formal calculus, hard‐disk encryption, or multi‐party protocols. However, up to now, there are not many schemes that achieve KDM‐CPA security, let alone KDM chosen ciphertext attack (KDM‐CCA) security. The constructions proposed by Camenisch, Chandran, and Shoup (Eurocrypt 2009), and Hofheinz (Eurocrypt 2013) are the only two general constructions that can be proved to be KDM‐CCA secure in the standard model. Besides, Qin, Liu, and Huang (ACISP 2013) also presented another concrete implementation. In particular, they showed how to obtain KDM‐CCA security from the classic Cramer–Shoup cryptosystem (based on the decisional Diffie–Hellman assumption) w.r.t. a new ensemble of functions (we call QLH ensemble). Since the Cramer–Shoup scheme has short ciphertext size and higher computational efficiency, they obtain practical KDM‐CCA security w.r.t. a reasonably large ensemble.In this paper, we study the KDM‐CCA security of other cryptosystems proposed by Cramer and Shoup (Eurocrypt 2002). In particular, we prove that the schemes, based on decisional composite residuosity (DCR) and quadratic residuosity (QR) assumptions, respectively, also achieve KDM‐CCA security w.r.t. the QLH ensemble. On the one hand, because the DCR‐based and QR‐based schemes of Cramer et al. are fairly practical, we also obtain practical KDM‐CCA security based on DCR and QR assumptions, respectively. On the other hand, compared with the result of Qin et al., we need not tailor the original schemes of Cramer et al. because themselves have natural “compatibility” for the message space and the secret key space. Copyright © 2014 John Wiley & Sons, Ltd.

Practical Fully Homomorphic Encryption for Integers over Polynomial Quotient Rings

In this article we describe a simplified version of Polly Cracker-style fully homomorphic encryption scheme. The main feature of our scheme is an ability to define a strict upper bound of ciphertext size when performing calculations on it for both addition and multiplication. Combined with homomorphic properties of Polly Cracker it's able to reach high calculation performance without degrading in time. Another important aspect is utilization of large finite rings for calculations in untrusted environment, which prevents most of known attacks on Polly Cracker family. Index Terms—fully homomorphic cryptography, finite integer rings, polynomials, polly cracker.

A Weakly Homomorphic Encryption with LDN

As an effective solution to protect the privacy of the data, homomorphic encryption has become a hot research topic. Existing homomorphic schemes are not truly practical due to their huge key size. In this paper, we present a simple weakly homomorphic encryption scheme using only elementary modular arithmetic over the integers rather than working with ideal lattices. Compared with DGHV’s construction, the proposed scheme has shorter public key and ciphertext size. The main appeal of our approach is the conceptual simplicity. We reduce the security of weakly homomorphic scheme to “learning divisor with noise (LDN)”

이진트리 기반의 속성기반 암호전송 알고리즘

In this paper, we present two constructions of the attribute-based broadcast encryption(ABBE) algorithm. Attribute-based encryption(ABE) algorithm enables an access control mechanism over encrypted data by specifying access policies among private keys and ciphertexts. ABBE algorithm can be used to construct ABE algorithm with revocation mechanism. Revocation has a useful property that revocation can be done without affecting any non-revoked uers. The main difference between our algorithm and the classical ones derived from the complete subtree paradigm which is apt for military hierarchy. Our algorithm improve the efficiency from the previously best ABBE algorithm, in particular, our algorithm allows one to select or revoke users by sending ciphertext of constant size with respect to the number of attributes and by storing logarithm secret key size of the number of users. Therefore, our algorithm can be an option to applications where computation cost is a top priority and can be applied to military technologies in the near future.

Chosen-ciphertext secure multi-hop identity-based conditional proxy re-encryption with constant-size ciphertexts

Proxy Re-Encryption (PRE) allows one user to delegate the decryption rights of his/her ciphertexts to another user. Since the introduction of Multi-Hop Identity-Based PRE (MH-IBPRE) by Green and Ateniese, the ciphertext size and the decryption complexity grow linearly in the number of re-encryption “hops”. In this paper, for the first time, we propose an MH-IBPRE that maintains the (constant) ciphertext size and computational complexity regardless of the number of re-encryption hops. Moreover, our scheme is bidirectional and also supports conditional re-encryption. The scheme is proven secure against selective identity and chosen-ciphertext attacks and collusion resistant in the standard model. As of independent interest, we also show that the conditional re-encryption can also be extended to a set of conditions.

Using Fully Homomorphic Hybrid Encryption to Minimize Non-interative Zero-Knowledge Proofs

A non-interactive zero-knowledge (NIZK) proof can be used to demonstrate the truth of a statement without revealing anything else. It has been shown under standard cryptographic assumptions that NIZK proofs of membership exist for all languages in NP. While there is evidence that such proofs cannot be much shorter than the corresponding membership witnesses, all known NIZK proofs for NP languages are considerably longer than the witnesses. Soon after Gentry's construction of fully homomorphic encryption, several groups independently contemplated the use of hybrid encryption to optimize the size of NIZK proofs and discussed this idea within the cryptographic community. This article formally explores this idea of using fully homomorphic hybrid encryption to optimize NIZK proofs and other related cryptographic primitives. We investigate the question of minimizing the communication overhead of NIZK proofs for NP and show that if fully homomorphic encryption exists then it is possible to get proofs that are roughly of the same size as the witnesses. Our technique consists in constructing a fully homomorphic hybrid encryption scheme with ciphertext size $$|m|+{\mathrm {poly}}(k)$$|m|+poly(k), where $$m$$m is the plaintext and $$k$$k is the security parameter. Encrypting the witness for an NP-statement allows us to evaluate the NP-relation in a communication-efficient manner. We apply this technique to both standard non-interactive zero-knowledge proofs and to universally composable non-interactive zero-knowledge proofs. The technique can also be applied outside the realm of non-interactive zero-knowledge proofs, for instance to get witness-size interactive zero-knowledge proofs in the plain model without any setup or to minimize the communication in secure computation protocols.

Efficient Anonymous Identity-Based Broadcast Encryption without Random Oracles

Broadcast encryption provides a method of secure multi-receiver communications, where a broadcaster can encrypt a message for a set S of users who are listening to a broadcast channel. Most identity-based broadcast encryption (IBBE) schemes are not anonymous, which means the attacker can obtain the identities of all receivers from the ciphertext. In this paper, the authors propose an efficient anonymous IBBE scheme in bilinear groups of prime order, where any attacker cannot get the identities of the receivers from the ciphertext. The scheme has constant size ciphertext and achieves adaptive security based on the asymmetric decisional bilinear Diffie-Hellman Exponent (DBDHE) assumption without random oracles. The proposed scheme improves efficiency and security of anonymous IBBE schemes simultaneously.

Simulation Study Based on Somewhat Homomorphic Encryption

At present study, homomorphic encryption scheme is most focusing on algorithm efficiency and security and the rare for homomorphic encryption simulation research. This paper for the Gentry’s Somewhat Homomorphic Encryption scheme for the simulation research, in clear text size within a certain range simulation was Somewhat Homomorphic Encryption scheme, and presents the relationship between the length of plaintext and ciphertext size.

New forward-secure public-key encryption without random oracles

Forward-secure public-key cryptography is an important technique for protecting private keys. It provides the benefits of frequent updating private keys without changing public keys. The most attractive property of forward security is that even if an attacker obtains the private key for the current time period, she still cannot compromise the private keys for the past time. In this paper, we newly present a forward-secure public-key encryption scheme without random oracles and prove it to be chosen-ciphertext secure in the standard model. In the proposed scheme, the ciphertext size and the decryption time have no correlation with the number of time periods and other performance indices have at most poly logarithmic complexities in terms of the number of time periods. As far as we know, it is the first forward-secure public-key encryption scheme that achieves direct chosen-ciphertext security in the standard model.