Short Ciphertexts Research Articles

Improved unbounded inner-product functional encryption

In this paper, we propose an unbounded inner-product functional encryption (unbounded IPFE) scheme with semi-adaptive simulation-based security. Compared with the previous semi-adaptive secure scheme proposed by Tomida and Takashima [Asiacrypt18], our scheme enjoys about 28% shorter ciphertext and about 43% shorter secret key.Technically, we start with a bounded separable one-key IPFE scheme. In the separable one-key IPFE scheme, the public key and ciphertext can be divided into some vectors. At the same time, we develop a new transformation from a bounded separable one-key IPFE scheme towards an unbounded IPFE scheme. Finally, we give a concrete instantiation with the bounded separable one-key IPFE scheme and the transformation.

A decentralized multi-authority CP-ABE scheme from LWE

As a cryptographic primitive supporting finer and richer access control, attribute-based encryption can provide more efficient, concise, secure and highly adaptive access control policies for cloud data, which has attracted the attention of many researchers. However, in a standard ABE scheme, the key can only be generated and issued by a central authority. The single authorization center has a heavy load and is vulnerable to attack. Once the center is paralyzed, it will bring serious security consequences. Multi-authorization center attribute encryption (MA-ABE) allows multiple parties to play an authoritative role, which can solve this problem.In this paper, we propose a MA-ABE scheme, which combines a global ID model, a two-stage sampling technique on a lattice and a monotonous linear secret sharing schemes (M-LSSS) to achieve a static security against arbitrary collusion in the random oracle model, in which the access policy of the scheme is expressed by DNF formula. Technically, our scheme is an improvement on the work of Datta et al. (2021), through this improvement, we can get shorter ciphertext and smaller key size.

Chosen-ciphertext secure code-based threshold public key encryptions with short ciphertext

Threshold public-key encryption (threshold PKE) has various useful applications. A lot of threshold PKE schemes are proposed based on RSA, Diffie–Hellman and lattice, but to the best of our knowledge, code-based threshold PKEs have not been proposed. In this paper, we provide three IND-CCA secure code-based threshold PKE schemes. The first scheme is the concrete instantiation of Dodis–Katz conversion (Dodis and Katz, TCC’05) that converts an IND-CCA secure PKE into an IND-CCA secure threshold PKE using parallel encryption and a signature scheme. This approach provides non-interactive threshold decryption, but ciphertexts are large (about 16 kilobytes for 128-bit security) due to long code-based signatures even in the state-of-the-art one. The second scheme is a new parallel encryption-based construction without signature schemes. Unlike the Dodis–Katz conversion, our parallel encryption converts an OW-CPA secure PKE into an OW-CPA secure threshold PKE. To enhance security, we use Cong et al.’s conversion (Cong et al., ASIACRYPT’21). Thanks to eliminating signatures, its ciphertext is 512 bytes, which is only 3% of the first scheme. The decryption process needs an MPC for computing hash functions, but decryption of OW-CPA secure PKE can be done locally. The third scheme is an MPC-based threshold PKE scheme from code-based assumption. We take the same approach Cong et al. took to construct efficient lattice-based threshold PKEs. We build an MPC for the decryption algorithm of OW-CPA secure Classic McEliece PKE. This scheme has the shortest ciphertext among the three schemes at just 192 bytes. Compared to the regular CCA secure Classic McEliece PKE, the additional ciphertext length is only 100 bytes. The cons are heavy distributed computation in the decryption process.

A CP-ABE Scheme Based on Lattice LWE and Its Security Analysis

In recent years, the research on ciphertext-policy attribute-based encryption (CP-ABE) scheme design based on learning with errors (LWE) has been a challenging problem, and many researchers have made a lot of attempts at it. At EUROCRYPT 2021, Datta, Komargodski, and Waters proposed the first provably secure direct CP-ABE construction that supports NC1 circuit access structures. Improving on their work, we propose a CP-ABE scheme. Technically, we use the new lattice two-stage sampling technique of Lai, Liu, and Wang (EUROCRYPT 2021) in the key generation phase instead of the extended trapdoor sampling technique. In this way, we obtain a CP-ABE scheme, which is at least as secure as the original scheme under the same conditions, and has a shorter ciphertext; we provide an innovative design idea for designing CP-ABE schemes only based on LWE, although this is only a partial theoretical work.

Generic Construction of Black-Box Traceable Attribute-Based Encryption

Attribute-based encryption (ABE) has been widely used to provide fine-grained access control to encrypted data in cloud computing. However, in practice, since the attributes are shared by multiple users in the ABE system, it is difficult to identify malicious users which intentionally but implicitly reveal their own ABE secret keys for some purpose. In recent years, a substantial amount of work focused on designing efficient tracing mechanisms to identify such misbehaving users on ABE. In this paper, we propose an efficient generic construction of black-box traceable ABE to identify the traitors. Our construction supports (public) adaptive black-box traceability and has short keys and short ciphertexts that are independent of the number of users. Technically, our construction relies on a generic transformation from any attribute-based inner-product functional encryption (ABIPFE) scheme to black-box traceable ABE system. Furthermore, to instantiate our generic construction from standard lattices, we propose the first lattice-based ABIPFE scheme, which is proven weakly selective secure in the standard model.

Fast keyword search over encrypted data with short ciphertext in clouds

Nowadays, it is convenient for people to store their data on clouds. To protect the privacy, people tend to encrypt their data before uploading them to clouds. Due to the widespread use of cloud services, public key searchable encryption is necessary for users to search the encrypted files efficiently and correctly. However, the existing public key searchable encryption schemes supporting monotonic queries suffer from either infeasibility in keyword testing or inefficiency such as heavy computing cost of testing, large size of ciphertext or trapdoor, and so on. In this work, we first propose a novel and efficient anonymous key-policy attribute-based encryption (KP-ABE). Then by applying Shen et al.’s generic construction to the proposed anonymous KP-ABE, we obtain an efficient and expressive public key searchable encryption, which to the best of our knowledge achieves the best performance in testing among the existing such schemes. Only 2 pairings are needed in testing. By applying our searchable encryption, one is able to expressively and efficiently search their encrypted data on clouds, without leaking the keyword information. Besides, we also implement our scheme and others with Python for comparing the performance. From the implementation results, our scheme owns the best performance on testing, and the size of ciphertexts and trapdoors are smaller than most of the existing schemes.

A direct construction of continuous leakage-resilient (H)IBE scheme with CCA security from dual system encryption

Continuous leakage resilient semantically secure Identity-based Encryption (IBE) schemes created with dual system encryption technique were presented by Lewko et al. at TCC 2011 and Yuen et al. at Eurocrypt 2012, respectively. It has been a research challenge to achieve the security against chosen-ciphertext attacks (CCA). The previous attempts toward the CCA security rely on q-type assumptions, which are referred as non-static assumptions causing loose reduction in security proofs. In this paper, we provide a complete solution to the problem and show how to construct the continuous leakage-resilient IBE with weaker CCA security based on the dual system encryption technique, where the adversary is allowed to make continuous leakage queries. We are able to prove its security with static assumptions in the standard model. As a feature of our scheme, we allow leakage of multiple keys, i.e., leakage of the master secret key and the private key of user. Our scheme also enjoys better computational performance, since the round leakage parameter is independent of the plaintext space and has a constant size. Furthermore, our scheme can be easily extended to give the weaker CCA secure continuous leakage-resilient hierarchical identity-based encryption scheme with a short ciphertext length.

A Generic Approach to Build Revocable Hierarchical Identity-Based Encryption

Revocable hierarchical identity-based encryption (RHIBE) is an extension of HIBE that provides the efficient key revocation function by broadcasting an update key per each time period. Many RHIBE schemes have been proposed by combining an HIBE scheme and a tree-based revocation method, but a generic method for constructing an RHIBE scheme has not been proposed. In this paper, we show for the first time that it is possible to construct RHIBE schemes by generically combining underlying cryptographic primitives and tree-based revocation methods. We first generically construct an RHIBE-CS scheme by combining HIBE schemes and the complete subtree (CS) method, and prove the adaptive security by using the adaptive security of the HIBE schemes. Thus, we obtain RHIBE schemes under the quadratic residuosity assumption, CDH assumption, and factoring assumption. Next, we generically construct an RHIBE-SD scheme with shorter update keys by combining HIBE and hierarchical single revocation encryption (HSRE) schemes, and the subset difference (SD) method to reduce the size of update keys. Finally, we generically construct an RHIBE-CS scheme with shorter ciphertexts by combining HIBE schemes with constant-size ciphertext and the CS method. Through different kind of generic combinations, we obtain various RHIBE schemes that provide a trade-off between shorter ciphertexts and shorter update keys.

Elizebeth Smith Friedman and one example of a prohibition era encryption system

A short ciphertext message encrypted using a Prohibition era encryption system is examined. First published in David Kahn’s The Codebreakers, this example appears in two early reports written by Elizebeth Smith Friedman. Some obvious and some not so obvious errors are identified and corrected when possible. Friedman’s cryptanalysis of the ciphertext is given.

Key Management Scheme for Secure Channel Establishment in Fog Computing

Fog computing is a promising extension of cloud computing, and enables computing directly at the edge of the network. Due to the decentralized and distributed nature of fog nodes, secure communication channels have to be supported in fog computing, which are generally realized through secure keys. Key management schemes are usually employed to generate, distribute and maintain the secret keys. In this paper, we propose a key management scheme called dynamic contributory broadcast encryption (DConBE) for secure channel establishment in fog computing. It allows a group of fog nodes that want to establish a fog system to negotiate a public encryption key and each node’s decryption key in one round without a trusted dealer. Any end user may encrypt messages under the public encryption key with short ciphertexts to any subset of the fog nodes in the system. Only selected fog nodes in the system can decrypt the encrypted messages using their respective decryption key. Our new key management scheme also achieves the properties of fog node dynamics, fully collusion-resistant and stateless.

How we set new world records in breaking Playfair ciphertexts

The Playfair cipher is a well-known manual encryption method developed in the 19th century. Until 2018, known cryptanalysis techniques, with computer assistance, could solve non-keyword-based Playfair ciphertexts if they had at least 60 letters to work with. Shorter ciphertexts were effectively impossible to solve in the absence of a crib. In this article, we show how we introduced several improvements in these cryptanalysis methods, which made it possible to do much better. This resulted in the (unofficial) world record for the shortest Playfair message broken going down from 60 via 50, 40, 32, and 28 to 26 letters. The cryptanalysis techniques used include hill climbing, simulated annealing, tabu search, and plaintext-based dictionary attacks. For readers interested in improving the current record, we also provide unsolved Playfair challenges consisting of 24 and 22 letters.

LIGA: a cryptosystem based on the hardness of rank-metric list and interleaved decoding

We propose the new rank-metric code-based cryptosystem LIGA which is based on the hardness of list decoding and interleaved decoding of Gabidulin codes. LIGA is an improved variant of the Faure–Loidreau (FL) system, which was broken in a structural attack by Gaborit, Otmani, and Talé Kalachi (GOT, 2018). We keep the FL encryption and decryption algorithms, but modify the insecure key generation algorithm. Our crucial observation is that the GOT attack is equivalent to decoding an interleaved Gabidulin code. The new key generation algorithm constructs public keys for which all polynomial-time interleaved decoders fail—hence LIGA resists the GOT attack. We also prove that the public-key encryption version of LIGA is IND-CPA secure in the standard model and the key encapsulation mechanisms version is IND-CCA2 secure in the random oracle model, both under hardness assumptions of formally defined problems related to list decoding and interleaved decoding of Gabidulin codes. We propose and analyze various exponential-time attacks on these problems, calculate their work factors, and compare the resulting parameters to NIST proposals. The strengths of LIGA are short ciphertext sizes and (relatively) small key sizes. Further, LIGA guarantees correct decryption and has no decryption failure rate. It is not based on hiding the structure of a code. Since there are efficient and constant-time algorithms for encoding and decoding Gabidulin codes, timing attacks on the encryption and decryption algorithms can be easily prevented.

Attribute-Based Fully Homomorphic Encryption Scheme from Lattices with Short Ciphertext

Attribute-based encryption (ABE) is a good choice for one-to-many communication and fine-grained access control of the encryption data in a cloud environment. Fully homomorphic encryption (FHE) allows cloud servers to make valid operations on encrypted data without decrypting. Attribute-based fully homomorphic encryption (ABFHE) from lattices not only combines the bilateral advantages/facilities of ABE and FHE but also can resist quantum attacks. However, in the most previous ABFHE schemes, the growth of ciphertext size usually depends on the total number of system’s attributes which leads to high communication overhead and long running time of encryption and decryption. In this paper, based on the LWE problem on lattices, we propose an attribute-based fully homomorphic scheme with short ciphertext. More specifically, by classifying the system’s attributes and using the special structure matrix in MP12, we remove the dependency of ciphertext size on system’s attributes ℓ and the ciphertext size is no longer increased with the total number of system’s attributes. In addition, by introducing the function G − 1 in the homomorphic operations, we completely rerandomize the error term in the new ciphertext and have a very tight and simple error analysis using sub-Gaussianity. Besides, performance analysis shows that when ℓ = 2 and n = 284 according to the parameter suggestion given by Micciancio and Dai et al., the size of ciphertext in our scheme is reduced by at least 73.3%, not to mention ℓ > 2 . The larger the ℓ , the more observable of our scheme. The short ciphertext in our construction can not only reduce the communication overhead but also reduce the running time of encryption and decryption. Finally, our scheme is proved to be secure in the standard model.

New Order-Revealing Encryption with Shorter Ciphertexts

As data outsourcing services have been becoming common recently, developing skills to search over encrypted data has received a lot of attention. Order-revealing encryption (OREnc) enables performing a range of queries on encrypted data through a publicly computable function that outputs the ordering information of the underlying plaintexts. In 2016, Lewi et al. proposed an OREnc scheme that is more secure than the existing practical (stateless and non-interactive) schemes by constructing an ideally-secure OREnc scheme for small domains and a “domain-extension” scheme for obtaining the final OREnc scheme for large domains. They encoded a large message into small message blocks of equal size to apply them to their small-domain scheme, thus their resulting OREnc scheme reveals the index of the first differing message block. In this work, we introduce a new ideally-secure OREnc scheme for small domains with shorter ciphertexts. We also present an alternative message-block encoding technique. Combining the proposed constructions with the domain-extension scheme of Lewi et al., we can obtain a new large-domain OREnc scheme with shorter ciphertexts or with different leakage information, but longer ciphertexts.

Public-Key Encryption Secure Against Related Randomness Attacks for Improved End-to-End Security of Cloud/Edge Computing

Public-key encryption is often used to protect data security/privacy and secure communication in scenarios of cloud computing and edge computing. Related randomness attacks model (RRA) for public-key encryption was motivated by randomness failures. This paper proposes some methods of constructing secure public-key encryption scheme against related randomness attacks, i.e. RRA-CPA secure public-key encryption scheme with efficient decryption algorithm and short ciphertexts size obtained from one-way function with weak RKA-security and indistinguishability obfuscation, RRA-CPA secure public-key encryption scheme against arbitrarily function from any publicly deniable encryption and RRA-CCA secure public-key encryption scheme against arbitrarily function from standard IND-CCA public-key encryption scheme with a hardcore function for arbitrarily correlated inputs.

Authenticated public key broadcast encryption with short ciphertexts

Broadcast encryption allows a broadcaster, who wants to distribute messages to a chosen subset of receivers, to produce an encrypted content and transmit it via a broadcast channel. Normally we think that it is preferable if the broadcast encryption system is a public-key cryptosystem, which permits anybody could encrypt and distribute messages with public parameters. Nevertheless, such a broadcast strategy brings along a slew of diffusions of the spam that are uncontrollable. Authenticated public key broadcast encryption ensures that no such strategy can succeed - the encryption algorithm creates ciphertext with public key and the broadcaster’s secret key. It means that each broadcasted message is associated to the content distributor in order to ensure accountability. Technically, it embeds a signature in the ciphertext and each authorized users could verify it during decrypting. In this paper, we construct a solution for authenticated public key broadcast encryption using bilinear maps where the ciphertext is of O(1) (only constant number of group elements). The public key size and user private key are of size O(N) (N is the total number of users). The simulation experiment results indicated that the size of public key (private key) is about 4MB where we arbitrarily set N = 100000. Finally, we define the security for authenticated public key broadcast encryption and show that our construction captures static security in the standard model.

Contributory Broadcast Encryption on Sharingdata Over Dynamic Group Key Agreement

The Multicasting with Key Administration enables every part to steadfastly keep up a solitary open key pair. To execute the encryption along with decoding ye transmitter and recipient ought to own comparing encryption along with unscrambling keys. For transportation safety measure data to aggregate required communicate encryption (BE). BE sanctions a sender to safely communicate to any subset of people and demand a believed gathering to disperse decoding keys. A sender seeing the open gathering encryption key can confine the decoding to a subset of people from his decision. Following this model, we propose a CBE conspire with short ciphertexts. The program is proved to be completely conspiracy safe under the option n-Bilinear Diffie-Hellman Exponentiation (BDHE) suspicion in the conventional model. As our exhibited frameworks expressed that communicate encryption (BE) is required for secure information redistributing over a gathering and Gathering key understanding (GKA) convention let'screate a classified channel among gathering individuals however because of lack of keymanagement and gathering part denial is an up to now testing issues. To beat the difficulties over prented framework we proposed a Symmetric key communicate encryption (SKBE) which drives the aforementioned issues adequately than our exhibited framework.

Public-Key Encryption with Integrated Keyword Search

Since the last decade, the public-key encryption with keyword search (PEKS) has been studied as a popular technique for searching data over encrypted files. The notion finds useful application for fine-grained data search on outsourced encrypted data like iCloud, mobile cloud data, etc. In this paper, we present a concrete public-key encryption (PKE)+PEKS scheme and prove its security in the standard model. We prove that our scheme is both IND-PKE-CCA secure, that is, provides message confidentiality against an adaptive chosen-ciphertext adversary, and IND-PEKS-CCA secure, that is, provides keyword privacy against an adaptive chosen-ciphertext adversary, under the Symmetric eXternal Diffie-Hellman (SXDH) assumption. Our construction uses asymmetric pairings which enable a fast implementation useful for practical applications. Our scheme has much shorter ciphertexts than other known PKE+PEKS schemes. Particularly, we compare our scheme with other proposed PEKS and integrated PKE+PEKS schemes and provide a relative analysis of various parameters including assumption, security, and efficiency.

Optimized Verifiable Fine-Grained Keyword Search in Dynamic Multi-owner Settings

Ciphertext-Policy Attribute-Based Keyword Search (CP-ABKS) schemes support both fine-grained access control and keyword-based ciphertext retrieval, which make these schemes attractive for resource-constrained users (i.e., mobile or wearable devices, sensor nodes, etc.) to store, share and search encrypted data in the public cloud. However, ciphertext length and decryption overhead in the existing CP-ABKS schemes grow with the complexity of access policies or the number of data users’ attributes. Moreover, such schemes generally do not consider the practical multi-owner setting (e.g., each file needs to be signed by multiple data owners before being uploaded to the cloud server) or prevent malicious cloud servers from returning incorrect search results. To overcome these limitations, in this paper we first design an optimized Verifiable Fine-grained Keyword Search scheme in the static Multi-owner setting (termed as basic VFKSM), which achieves short ciphertext length, fast ciphertext transformation, accelerated search process, and authentic search result verification. Then, we extend the basic VFKSM to support multi-keyword search and multi-owner update (also called as extended VFKSM). Finally, we prove that the basic (or extended) VFKSM resists the Chosen-Keyword Attack (CKA) and external Keyword-Guessing Attack (KGA). We also evaluate the performance of these schemes using various public datasets.

Securing content-centric networks with content-based encryption

As content is transmitted in content-driven manner in the content-centric network (CCN), it does not require any host address; therefore, it is infeasible to establish a traditional secure channel between hosts. Securing the content transmission in the CCN is a challenging problem. We solve this problem with the content-based encryption, where the encryption key is associated with the content itself, and the private decryption keys are distributed to the authorized consumers. To deal with the security requirements for content-based encryption, we define a security model that captures the key existential unforgeability and semantic security. We then propose a content-based encryption scheme with short ciphertexts, which is proven to be strong key existentially unforgeable and semantically secure in the standard model. We apply the scheme to construct a secure content transmission protocol in the CCN, which captures the security properties of content confidentiality, integrity, resistance to replay attacks and resistance to key forgery attacks. The performance analysis shows that our protocol is efficient for large content transmission.