Ciphertext Size Research Articles

Complementary set encryption for privacy-preserving data consolidation

Privacy-preserving data consolidation is one of the prominent research topics in the big data era, mostly because of the need of consolidating data from various database communities, which are highly sensitive or competitive in nature. This leads to a new emerging problem namely how to accomplish data consolidation among different organization data sets or databases appropriately without revealing any competitive or sensitive information to non-owners. To address this issue, we first introduce a new encryption notion called “complementary set encryption” (CSE) to apply to privacy-preserving data consolidation. In this notion, to provide privacy protection, the data in one database will be encrypted under a set W prior to being sent to the other database, and a decryption key will be generated with another set Q. The data will be decrypted and consolidated into the other database, if and only if both sets W and Q are complementary. Here, the “complementary” means that the intersection of set W and set Q is empty and meanwhile the union of both is to be completed into a universal set exactly. We then describe two constructions of CSE under the public-key setting. Our first construction is designed under a weaker security notion – “payload hiding”, which only preserves the data privacy but achieves a higher performance. The second construction is a stronger security notion, which we refer to as an “attribute hiding”, which preserves both the privacy of the data and its associated set W. Finally, we provide a formal analysis to prove the security of our two constructions, followed by a theoretical performance comparison and an experimental evaluation. In particular, the first construction is of an independent interest in the context of cryptography since it was able to stand out for its efficiency as a predicate encryption scheme in the sense that it features both low communication overhead and computational costs simultaneously, and only requires a private key size of O(1), a ciphertext size of O(1), and only O(1) pairing computations.

MACFI: A multi-authority access control scheme with efficient ciphertext and secret key size for fog-enhanced IoT

With the rapid development of Internet of things (IoT), the number of connected devices and the data generated by them are increasing dramatically. This led to the development of paradigm fog computing, which facilitates data analysis and processing at the edge. Along with fog, cloud co-exists to provide massive storage, processing resources, etc. However, data storage and computation at multiple levels raise the risk of data security. Ciphertext-policy attribute-based encryption (CP-ABE) is a well-known cryptographic technique for providing fine-grained access control. Unfortunately, the existing multi-authority CP-ABE schemes are incompatible with resource-limited IoT devices as the ciphertext and secret key size grow linearly with the number of attributes. Therefore, we propose a multi-authority CP-ABE scheme named MACFI, where the ciphertext and secret key size are efficient. The size of the secret key held by the user is constant irrespective of the number of attributes. And, the ciphertext size increases linearly with the number of authorities rather than the number of attributes. Further, expensive decryption operations are outsourced to fog, which reduces the computation overhead of data users. Additionally, the overall encryption and decryption time are highly efficient. According to security and performance analysis, MACFI is secure and suitable for IoT applications.

MLS-ABAC: Efficient Multi-Level Security Attribute-Based Access Control scheme

Realizing access control to sensitive data offloaded to a Cloud is challenging in the Internet of Things, where various devices with low computational power and different security levels are interconnected. Despite various solutions, the National Institute of Standards and Technology (NIST)’s Attribute-Based Access Control (ABAC) model is one of the preferred techniques in the literature. In this model, users who satisfy access policies using both static and dynamic attributes are allowed to access the data. However, NIST’s ABAC model does not support encryption and therefore does not satisfy data confidentiality. Attribute-Based Encryption (ABE) is a known cryptographic primitive that enables fine-grained access control over encrypted data. However, currently the existing ABE schemes do not meet NIST’s ABAC requirements or are not computationally efficient enough for IoT applications. In this paper, we propose a Multi-Level Security ABAC (MLS-ABAC) scheme that satisfies the requirements of NIST’s ABAC model. Our construction is efficient and relies on a decryption outsourceable Ciphertext-Policy ABE scheme. Additionally, based on realistic application scenarios, only the authorized data users can decrypt the ciphertext, and check the integrity of the retrieved message. Furthermore, we present both conceptual and formal models for our proposed MLS-ABAC architecture along with performance metrics. The experimental results show that the proposed MLS-ABAC achieves a constant ciphertext size of ∼230 bytes and with encryption and decryption running times of ∼18 and ∼10 ms, respectively, independent of the number of attributes.

Decentralized Inner-Product Encryption with Constant-Size Ciphertext

With the rise of technology in recent years, more people are studying distributed system architecture, such as the e-government system. The advantage of this architecture is that when a single point of failure occurs, it does not cause the system to be invaded by other attackers, making the entire system more secure. On the other hand, inner product encryption (IPE) provides fine-grained access control, and can be used as a fundamental tool to construct other cryptographic primitives. Lots of studies for IPE have been proposed recently. The first and only existing decentralized IPE was proposed by Michalevsky and Joye in 2018. However, some restrictions in their scheme may make it impractical. First, the ciphertext size is linear to the length of the corresponding attribute vector; second, the number of authorities should be the same as the length of predicate vector. To cope with the aforementioned issues, we design the first decentralized IPE with constant-size ciphertext. The security of our scheme is proven under the ℓ-DBDHE assumption in the random oracle model. Compared with Michalevsky and Joye’s work, ours achieves better efficiency in ciphertext length and encryption/decryption cost.

Binary Multifold Encryption Technique for Complex Cloud Systems

Data security is a major cloud computing issue due to different user transactions in the system. The evolution of cryptography and cryptographic analysis are regarded domains of current research. deoxyribo nucleic acid (DNA) cryptography makes use of DNA as a sensing platform, which is then manipulated using a variety of molecular methods. Many security mechanisms including knowledge-based authentication, two-factor authentication, adaptive authentication, multifactor authentication and single password authentication have been deployed. These cryptographic techniques have been developed to ensure confidentiality, but most of them are based on complex mathematical calculations and equations. In the proposed approach, a novel and unique Hybrid helix scuttle-deoxy ribo nucleic acids (HHS-DNA) encryption algorithm has been proposed which is inspired by DNA cryptography and Helix scuttle. The proposed HHS-DNA is a type of multifold binary version of DNA (MF-BDNA). The major role of this paper is to present a multifold HHS-DNA algorithm to encrypt the cloud data assuring more security with less complexity. The experimentation is carried out and it reduces the encryption time, cipher text size, and improves throughput. When compared with previous techniques, there is a 45% improvement in throughput, 37% fast in encryption time, 54.67% cipher text size. The relevant experimental results and foregoing analysis show that this method is of good robustness, stability, and security.

An Enhanced Approach for CP-ABE with Proxy Re-encryption in IoT Paradigm

In Internet of Things (IoT), encryption is a technique in which plaintext is converted to ciphertext to make it non-recovered by the attacker without secret key. Ciphertext policy attribute based encryption (CP-ABE) is an encryption technique aimed at multicasting feature i.e. user can only decrypt the message if policy of attributes mentioned in ciphertext is satisfied by the user’s secret key attributes. In literature, the authors have improvised the existing technique to enhance the naïve CP-ABE scheme. Recently, in 2021, Wang et al. have proposed the CP-ABE scheme with proxy re-encryption and claimed it to be efficient as to its predecessors. However, it follows the variable length ciphertext in which size of ciphertext is increased with the number of attributes. Also, it leads to computation overhead on the receiver during decryption which will be performed by the IoT devices. Thus, in this paper we have proposed the improved scheme to provide the constant length ciphertext with proxy re-encryption to reduce the computation and communication time. The proposed scheme is secured under Decisional Bilinear Diffie-Hellman (DBDH) problem.

An improved approach in CP-ABE with proxy re-encryption

A cryptographic encryption technique converts plaintext into ciphertext, which is non-recoverable by a malicious user without knowing the secret key. The Ciphertext Policy Attribute Based Encryption (CP-ABE) scheme aims for a multicast feature. Different users can decrypt the message if their secret key attributes match with the policy of attributes defined in the ciphertext. In literature, various approaches exist to enhance the naïve CP-ABE scheme. In 2021, Wang et al. proposed the proxy re-encryption-based CP-ABE scheme and presented that it is efficient as its predecessors. However, the proposed scheme follows the variable-length ciphertext where the ciphertext size depends on the number of attributes. Such variable-length ciphertext increases the required number of operations for the decryption, leading to the computation overhead at the receiver side. This paper proposes an enhanced CP-ABE-CL-PRE (CP-ABE Constant Length with PRE) scheme to provide the constant length ciphertext with proxy re-encryption. Our proposed scheme is secure under the Decisional Bilinear Diffie-Hellman (DBDH) problem.

Efficient Lattice-Based Cryptosystems with Key Dependent Message Security

Key-dependent message (KDM) security is of great research significance, to better analyse and solve the potential security problems in complex application scenarios. Most of the current KDM security schemes are based on traditional hard mathematical problems, where the public key and ciphertext are not compact enough, and make the ciphertext size grow linearly with the degree of the challenge functions. To solve the above problems and the inefficient ciphertext operation, the authors propose a compact lattice-based cryptosystem with a variant of the RLWE problem, which applies an invertible technique to obtain the RLWE* problem. It remains hard after the modification from the RLWE problem. Compared with the ACPS scheme, our scheme further expands the set of challenge functions based on the affine function of the secret key, and the size of public key and ciphertext is O˜(n), which is independent of the challenge functions. In addition, this scheme enjoys a high level of efficiency, the cost of encryption and decryption is only ploylog(n) bit operations per message symbol, and we also prove that our scheme is KDM-CPA secure under the RLWE* assumption.

A Blockchain-Based CP-ABE Scheme with Partially Hidden Access Structures

Data sharing has become a key technology to break down data silos in the big data era. Ciphertext-policy attribute-based encryption (CP-ABE) is widely used in secure data-sharing schemes to realize flexible and fine-grained access control. However, in traditional CP-ABE schemes, the access structure is directly shared along with the ciphertext, potentially leading to users’ private information leakage. Outsourcing data to a centralized third party can easily result in privacy leakage and single-point bottlenecks, and the lack of transparency in data storage and sharing casts doubts whether users’ data are safe. To address these issues, we propose a blockchain-based CP-ABE scheme with partially hidden access structures (BCP-ABE-PHAS) to achieve fine-grained access control while ensuring user privacy. First, we propose an efficient CP-ABE scheme with partially hidden access structures, where the ciphertext size is constant. To assist data decryption, we design a garbled Bloom filter to help users quickly locate the position of wildcards in the access structure. Then, to improve storage efficiency and system scalability, we propose a data storage scheme that combines blockchain technology and the interplanetary file system, ensuring data integrity. Finally, we employ smart contracts for a transparent data storage and sharing process without third-party participation. Security analysis and performance evaluation show that the proposed BCP-ABE-PHAS scheme can preserve policy privacy with efficient storage and low computational overhead.

Efficient SMC Protocol Based on Multi-Bit Fully Homomorphic Encryption

Aiming at the problems of large ciphertext size and low efficiency in the current secure multi-party computation (SMC) protocol based on fully homomorphic encryption (FHE), the paper proves that the fully homomorphic encryption scheme that supports multi-bit encryption proposed by Chen Li et al. satisfies the key homomorphism. Based on this scheme and threshold decryption, a three-round, interactive, leveled, secure multi-party computation protocol under the Common Random String (CRS) model is designed. The protocol is proved to be safe under the semi-honest model and the semi-malicious model. From the non-interactive zero-knowledge proof, it can be concluded that the protocol is also safe under the malicious model. Its security can be attributed to the Decisional Learning With Errors (DLWE) and a variant of this problem (some-are-errorless LWE). Compared with the existing secure multi-party computation protocol based on fully homomorphic encryption under the CRS model, the ciphertext size of this protocol is smaller, the efficiency is higher, the storage overhead is smaller, and the overall performance is better than the existing protocol.

Security analysis of uppercaseSM9 digital signature and key encapsulation

Security analysis provides strong guarantees and evidence for security cryptosystems. SM9 is an identity-based cryptosystem designed by China and has become a Chinese standard. The SM9 digital signature and encryption algorithm also became ISO/IEC International standards. However, there are few published research results on the security of SM9 cryptosystems. Based on Gap-$q$-BCAA1 assumption, Cheng gave the security analysis of SM9 key exchange protocol, key encapsulation and encryption algorithm in Inscrypt 2018. In this paper, we first give the formal security analysis for SM9 digital signature. Based on the $q$-SDH assumption, we prove that SM9 signature algorithm is EUF-CMIA secure. To eliminate the Gap assumption, we then use the technique of Twin-Hash-ElGamal to modify SM9 key encapsulation slightly without compromising its security and propose a new identity-based key encapsulation mechanism called Twin-SM9. Compared to SM9 key encapsulation, both the system public key and user private key contain one additional group element only and the ciphertext size remains the same. We prove that Twin-SM9 achieves IND-CCA security in the random oracle model based on the $q$-BDHI assumption. Our results clarify the security of SM9 and are useful for the design of SM9-based cryptosystems.

Fast Strategies for the Implementation of SIKE Round 3 on ARM Cortex-M4

The Supersingular Isogeny Key Encapsulation mechanism (SIKE) is the only post-quantum key encapsulation protocol based on elliptic curves and isogeny maps between them. Despite the quantum security of the protocol, SIKE requires a greater number of clock cycles and hence does not provide competitive timing and energy consumption results. However, it is more attractive offering the smallest public key as well as ciphertext sizes, which considering the impact of the communication costs and storage of the keys could become a good fit for resource-constrained devices. In this work, we present the fastest practical implementation of SIKE, targeting the platform Cortex-M4 based on the ARMv7-M architecture. We performed our measurements on the STM32F407VG microcontroller for benchmarking the clock cycles and on Nucleo-F411RE attached to X-NUCLEO-LPM01A (Power Shield) for measuring the energy consumption of the protocol. The low-level finite field arithmetic operations play main role in determining the efficiency of SIKE. Therefore, we mainly focus on their optimization and apply them to all NIST-required security levels. Our SIKEp434 implementation for NIST security level 1 is about 22.97% faster than the counterparts appeared in Seo <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2020), where for the SIKEp503, SIKEp610 and SIKEp751 the speedup reaches 21.10%, 19.21% and 19.08%. Finally, we benchmark energy consumption and report optimization of up to 11.9% depending on the NIST security level implementation.

Efficient identity-based encryption with Hierarchical key-insulation from HIBE

Hierarchical key-insulated identity-based encryption (HKIBE) is identity-based encryption (IBE) that allows users to update their secret keys to achieve (hierarchical) key-exposure resilience, which is an important notion in practice. However, existing HKIBE constructions have limitations in efficiency: sizes of ciphertexts and secret keys depend on the hierarchical depth. In this paper, we first triumph over the barrier by proposing simple but effective design methodologies to construct efficient HKIBE schemes. First, we show a generic construction from any hierarchical IBE (HIBE) scheme that satisfies a special requirement, called MSK evaluatability introduced by Emura et al. (Des. Codes Cryptography 89(7):1535–1574, 2021). It provides several new and efficient instantiations since most pairing-based HIBE schemes satisfy the requirement. It is worth noting that it preserves all parameters’ sizes of the underlying HIBE scheme, and hence we obtain several efficient HKIBE schemes under the k-linear assumption in the standard model. Since MSK evaluatability is dedicated to pairing-based HIBE schemes, the first construction restricts pairing-based instantiations. To realize efficient instantiation from various assumptions, we next propose a generic construction of an HKIBE scheme from any plain HIBE scheme. It is based on Hanaoka et al.’s HKIBE scheme (Asiacrypt 2005), and does not need any special properties. Therefore, we obtain new efficient instantiations from various assumptions other than pairing-oriented ones. Though the sizes of secret keys and ciphertexts are larger than those of the first construction, it is more efficient than Hanaoka et al.’s scheme in the sense of the sizes of master public/secret keys.

Efficient multi‐key fully homomorphic encryption over prime cyclotomic rings with fewer relinearisations

Multi-key fully homomorphic encryption (MKFHE) allows computations on ciphertexts encrypted by different users, which can be applied to implement secure multi-party computing (MPC). The current NTRU-based MKFHE has the following two drawbacks: One is that the relinearisation process during homomorphic evaluation is so complicated that the corresponding computation time is costly. The other is that a class of subfield attacks are proposed and affects the security of NTRU schemes over power-of-2 cyclotomic rings for large moduli q, especially for the NTRU-based fully homomorphic encryption (FHE) schemes. In this work, an efficient MKFHE scheme is proposed over prime cyclotomic rings with fewer relinearisations, which seems a good choice because of its potential to resist a subfield attack. More specifically, the time of the relinearisation process is reduced by half in homomorphic evaluations by separating the homomorphic multiplication and the relinearisation process (implementing two homomorphic multiplication operations together before relinearisation), while in current NTRU-type MKFHE schemes, these two processes are usually performed together. The error bound of the basic function components is re-analysed over prime cyclotomic rings in the average case, which can be used in the error analysis of our scheme. We construct an efficient NTRU-based single-key FHE scheme and an efficient MKFHE scheme over prime cyclotomic rings through relinearisation and modulus-switching techniques. The MKFHE scheme proposed has the on-the-fly property and has a tight ciphertext size compared with the GSW-type and BGV-type MKFHE schemes. An experiment shows that the homomorphic evaluation of the optimised single-key FHE scheme proposed is 1.9 times faster than an efficient NTRU-type MKFHE DHS16 proposed at DCC 2016.

Granular Data Access Control with a Patient-Centric Policy Update for Healthcare.

Healthcare is a multi-actor environment that requires independent actors to have a different view of the same data, hence leading to different access rights. Ciphertext Policy-Attribute-based Encryption (CP-ABE) provides a one-to-many access control mechanism by defining an attribute’s policy over ciphertext. Although, all users satisfying the policy are given access to the same data, this limits its usage in the provision of hierarchical access control and in situations where different users/actors need to have granular access of the data. Moreover, most of the existing CP-ABE schemes either provide static access control or in certain cases the policy update is computationally intensive involving all non-revoked users to actively participate. Aiming to tackle both the challenges, this paper proposes a patient-centric multi message CP-ABE scheme with efficient policy update. Firstly, a general overview of the system architecture implementing the proposed access control mechanism is presented. Thereafter, for enforcing access control a concrete cryptographic construction is proposed and implemented/tested over the physiological data gathered from a healthcare sensor: shimmer sensor. The experiment results reveal that the proposed construction has constant computational cost in both encryption and decryption operations and generates constant size ciphertext for both the original policy and its update parameters. Moreover, the scheme is proven to be selectively secure in the random oracle model under the q-Bilinear Diffie Hellman Exponent (q-BDHE) assumption. Performance analysis of the scheme depicts promising results for practical real-world healthcare applications.

Adaptively secure revocable hierarchical IBE from k-linear assumption

Revocable identity-based encryption (RIBE) is an extension of IBE with an efficient key revocation mechanism. Revocable hierarchical IBE (RHIBE) is its further extension with key delegation functionality. Although there are various adaptively secure pairing-based RIBE schemes, all known hierarchical analogues only satisfy selective security. In addition, the currently known most efficient adaptively secure RIBE and selectively secure RHIBE schemes rely on non-standard assumptions, which are referred to as the augmented DDH assumption and q-type assumptions, respectively. In this paper, we propose a simple but effective design methodology for RHIBE schemes. We provide a generic design framework for RHIBE based on an HIBE scheme with a few properties. Fortunately, several state-of-the-art pairing-based HIBE schemes have the properties. In addition, our construction preserves the sizes of master public keys, ciphertexts, and decryption keys, as well as the complexity assumptions of the underlying HIBE scheme. Thus, we obtain the first RHIBE schemes with adaptive security under the standard k-linear assumption. We prove adaptive security by developing a new proof technique for RHIBE. Due to the compactness-preserving construction, the proposed R(H)IBE schemes have similar efficiencies to the most efficient existing schemes.

A public key encryption scheme based on a new variant of LWE with small cipher size

The lattice cryptosystem is considered to be able to resist the attacks of quantum computers. Lattice-based Public Key Encryption (PKE) schemes have attracted the interest of many researchers. In lattice-based cryptography, Learning With Errors (LWE) problem is a hard problem usually used to construct PKE scheme. To ensure the correctness of decryption, LWE-based schemes have a large ciphertext size. This makes these encryption schemes not practical enough when the communication bandwidth is limited. We propose a new variant of LWE, named Learning With Modulus (LWM) and prove that the new problem can be reduced from LWE problem. The proof idea of our reduction is similar to the reduction of LWR problem. We also construct a new PKE scheme based on the proposed LWM and LWE, which has small ciphertext size. For a 128 bits plaintext, the ciphertext size of our scheme is 53.57% of Lindner–Peikert’s (LP) scheme under the same security level. We use python to test the performance of our scheme. The results show that our scheme is only about 0.015 ms slower than LP in the decryption. The performance of our scheme for generating keys and encrypting messages is similar to LP.

ETPAC: ECC based trauma plight access control for healthcare Internet of Things

Healthcare Industry experiences a rapid change in the traditional way of providing Medical Services to Patients with the revolution of the Internet of Things (IoT) and the Digitization of services. The Healthcare IoT (HIoT) provides Hospitals to render excellent services to Patients at an optimized cost. The Healthcare IoT must ensure not to disrupt or tamper with sensitive Medical Information of the Patient in addition to the continuous availability of data and services. The proposed framework is designed for secure emergency access to Patient data over Healthcare IoT. Normally, the Doctor obtains the Shared Key directly from the Patient to access the Medical data. In Trauma Plight, a Patient pre-shares an Attribute based Key with a set of Secondary Authority in Trauma Plight (SATP) and access permission to the Doctor for utilizing Emergency Key from SATP. The Doctor retrieves the medical record by using the Attribute based key and the Emergency-key to medicate the Patient in Trauma. The proposed ECC model based Trauma Plight Access Control (ETPAC) reduces the Shared Secret Key generation time, Encryption, Decryption Time, Cipher-Text size with low Secret Key Size. The performance analysis indicates the enhanced security with reduced time complexity of Computation and Communication in ETPAC compared to Lightweight Break-glass Access Control, an Efficient Policy Hiding Attribute Based Access Control, and an Efficient and Robust Attribute based Encryption Supporting Access Policy Hiding in Healthcare IoT.

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.

Do not ask me what I am looking for: Index deniable encryption

In this network era, the cloud storage service has become increasingly important. People have become used to storing data on the cloud and accessing them anytime, anywhere. However, due to privacy issues, data should be encrypted before being uploaded to the cloud. Thus, determining how to obtain the designated data from ciphertexts is important. In recent years, numerous searchable encryption schemes have been proposed. Most of these schemes do not consider the case wherein the search behavior is monitored, and there may come a time when users will be forced to open their search records and results. Thus, in this paper, an index deniable encryption scheme that supports both searchability and deniability is proposed to ensure user privacy in the cloud storage and the outside coercion case. We integrate the Bloom filter and the CP-ABE technique to construct a searchable encryption scheme. With the redundant keyword design, the search result can be opened to a fake data for the outside coercer. The proposed work has a constant ciphertext size to multiple deniable possibilities.