Certificate Revocation Research Articles

Revocable and Fog-Enabled Proxy Re-Encryption Scheme for IoT Environments.

As technology advances rapidly, a diverse array of Internet of Things (IoT) devices finds widespread application across numerous fields. The intelligent nature of these devices not only gives people more convenience, but also introduces new challenges especially in security when transmitting data in fog-based cloud environments. In fog computing environments, data need to be transmitted across multiple devices, increasing the risk of data being intercepted or tampered with during transmission. To securely share cloud ciphertexts, an alleged proxy re-encryption approach is a commonly adopted solution. Without decrypting the original ciphertext, such a mechanism permits a ciphertext intended for user A to be easily converted into the one intended for user B. However, to revoke the decryption privilege of data users usually relies on the system authority to maintain a user revocation list which inevitably increases the storage space. In this research, the authors come up with a fog-based proxy re-encryption system with revocable identity. Without maintaining the traditional user revocation list, the proposed scheme introduces a time-updated key mechanism. The time-update key could be viewed as a partial private key and should be renewed with different time periods. A revoked user is unable to obtain the renewed time-update key and hence cannot share or decrypt cloud ciphertexts. We formally demonstrate that the introduced scheme satisfies the security of indistinguishability against adaptively chosen identity and chosen plaintext attacks (IND-PrID-CPA) assuming the hardness of the Decisional Bilinear Diffie-Hellman (DBDH) problem in the random oracle model. Furthermore, compared with similar systems, the proposed one also has lower computational complexity as a whole.

SECURITY AND PERFORMANCE ENHANCEMENT USING SHORT-LIVED CERTIFICATES. A COMPREHENSIVE ANALYSIS

Short-lived certificates (SLC) are a comparatively new approach to improving software systems' security, performance, and effectiveness. A typical certificate validity can range anywhere between 12 months to multiple years. Short-lived certificates dramatically reduce the validity period to months, sometimes days, and, for some situations, even hours. By reducing the validity, they minimize the scope of damages if the private key is ever compromised. This paper examines the benefits of short-lived certificates, which include but are not limited to improved security posture and reduced reliance on certificate revocation infrastructure and mechanisms. We will approach the automation and infrastructure changes that made this new approach practical. We will explore methods of implementing such a system at scale. We will analyze the trade-offs between security, reliability, performance, and operational complexity. We will additionally cover the network and infrastructure changes that might be necessary for a reliable implementation of Short-lived certificates infrastructure.

A revocable and comparable attribute-based signature scheme from lattices for IoMT

The Internet of Medical Things (IoMT) refers to the utilization of the Internet of Things (IoT) technology in the healthcare industry. Access control is particularly important for IoMT due to the sensitive nature of patient data, such as electronic health records (EHR). Although fine-grained access control can be achieved by attribute-based signature (ABS), existing ABS schemes lacks the ability to provide range comparison access policy in which patients can check whether the attribute value is within a certain range. In addition, the dynamic change of doctors’ permissions and the development of quantum technology also require that ABS can provide user revocation and resist quantum attacks. In order to solve these problems and make ABS schemes for IoMT more useful and more secure, we come up with a novel revocable and comparable ABS (RC-ABS) from lattices for IoMT, enabling fine-grained access control, attribute range comparison, and user revocation. First of all, we provide a proof of the unforgeability of our scheme in the standard model (SM) under the selective user revocation list semi-adaptive attribute adaptive message attack, which can resist attacks by semi-honest adversaries and prevent adversaries from attacking the weaknesses of hash functions in IoMT. Furthermore, our ABS scheme leverages the small integer solution problem (SIS) to effectively defends against quantum algorithm attacks. Finally, detailed performance analysis demonstrates that our solution not only possesses enhanced security features and functionalities, such as revocability, comparability, and resistance against quantum attacks, but also maintains a constant computation cost of user revocation, making it more efficient compared to other revocation schemes.

Shared group session key-based conditional privacy-preserving authentication protocol for VANETs

Vehicular Ad-Hoc Networks (VANETs) have significantly enhanced driving safety and comfort by leveraging vehicular wireless communication technology. Due to the open nature of VANETs, conditional privacy-preserving authentication protocol should be offered against potential attacks. Efficient and secure authentication among vehicles in VANETs are important requirements, but there are various limitations in the existing conditional privacy-preserving authentication protocols for securing VANETs. To cope with the inherent issues, we propose a conditional privacy-preserving authentication protocol based share group session key (SGSK) by integrating the self-healing key distribution technique, blockchain, and MTI/C0 protocol. In our protocol, we use SGSK instead of the time-consuming Certificate Revocation List (CRL) checking, and we revoke malicious vehicles by updating SGSK. It is shared among unrevoked vehicles within a domain and across-domain. As a result, when a malicious revoked vehicle enters a new domain, it is difficult for it to access the system and send false messages. Furthermore, our protocol can not only achieve computation efficiency by reducing the number of computing operations of bilinear pairing but also resist various attacks while keeping conditional privacy protection. We implement our protocol in the Hyperledger Fabric platform. The experimental results show that our protocol is available to revoke 180 malicious vehicles in across-domain scenarios within one second, and it can meet the requirement of verifying 600 messages per second easily. Moreover, our comprehensive performance evaluations demonstrates that our protocol outperforms other approaches in terms of vehicle revocation checking cost, computation overhead, and communication overhead. In addition, to show the feasibility and validity of our protocol, we use SUMO and NS2 to simulate the actual VANET scenario and validate the efficiency and performance of our protocol. Simulation results prove the practicability of our protocol for VANETs.

Business Responsibilities for Food Products in the Don't Have Self Declare Category Halal Label (Case Study in Mataram City)

This research aims to analyze the responsibility of business actors towards ingredients that do not yet have a halal label according to positive law and to analyze the inhibiting factors in the responsibility of business actors towards self-declared food products. which does not have a halal label in Mataram City. By using empirical normative legal research methods. The results of this research show that to protect consumer rights, the Consumer Protection Law Number 8 of 1999 and other laws and regulations apply administrative and criminal sanctions to business actors, if business actors are proven to have violated the regulations that have been established in carrying out their activities. or offer its products. Materials that do not yet have a halal label according to positive law, as in Article 8 paragraph (1) letter h UUPK, stipulate that business actors are prohibited from producing and/or trading goods. As stated in the "halal" statement on the label. And Article 4 of Law Number 33 of 2014 concerning Halal Product Guarantees states that products entering, circulating and being traded in Indonesian territory must be halal certified. With this article, all products circulating in Indonesia must have a halal certificate, without exception, products from Micro, Small Enterprises (UMK) which should also have a halal certificate because they are already circulating on the market. Legal responsibility for business actors who do not yet have a halal label for their products. Administrative/administrative sanctions are given , namely sanctions imposed due to administrative violations or legal provisions of an administrative nature, up to fines, revocation of certificates and/or permits, temporary suspension of administrative services up to reduction of production quotas. Inhibiting factors in the responsibility of business actors for self-declared food products which do not have a halal label in Mataram City, the inhibiting factors consist of two factors, namely: a. Internal factors consist of business actors' knowledge of halal certification, knowledge of halal certification obligations and certification costs. b. External factors consist of lack of socialization from the Halal Center Institute at UIN Mataram and lack of consumer awareness.

Verifying Certificate Revocation Status for Short Key Lengths in Vehicle Communication Systems

This paper proposes and analyzes a ticket-based OCSP protocol for efficient certificate revocation checking in vehicle communication systems. The IEEE WAVE standard for vehicular networks requires real-time processing of Basic Safety Messages (BSMs) exchanged between vehicles. Traditional OCSP revocation checking can introduce delays. The proposed approach distributes OCSP responses as tickets valid for a road section. Vehicles use shorter keys extracted from the tickets for faster cryptographic processing. Experiments compare processing times for signature generation and verification with different elliptic curves. The results show the proposed technique provides faster revocation checking. This allows time-critical vehicle-to-vehicle message processing at high rates under computational constraints. The ticket-based OCSP mechanism enhances security while meeting real-time requirements in vehicular networks.

Analysis of non-compliances identified in GMP inspections between 2013 and 2022

Ensuring the quality and safety of medicinal products is of paramount importance to the pharmaceutical industry. Good manufacturing practice (GMP) regulations are part of a pharmaceutical manufacturer’s quality management system and ensure that medicinal products are manufactured, imported and controlled consistently to quality standards appropriate to their intended use. The aim of the present study is to analyze the non-compliant operations identified during GMP inspections carried out by national competent authorities (NCA) in the EU/EEC between 2013 and 2022. A retrospective analysis of non-compliance reports published in the EudraGMDP database between 2013 and 2022 was performed. Overall, 99 reports by 21 national competent authorities were analyzed presenting the results of inspections in 19 countries. A total of 1458 deficiencies were identified, of which 544 (37%) were classified as major and 127 (9%) as critical. The most common non-compliant operations were the manufacturing of active substances (49 deficiencies) and the preparation of non-sterile products (47 deficiencies). In 41 cases, the NCA recommended suspension or voiding of the certificate of suitability (CEP) and in 36 cases revocation of the GMP certificates. The observed deficiencies highlight the importance and need for continuous monitoring and improvement of manufacturers’ production processes and quality management systems.

Security in Optical Wireless Communication-Based Vehicular Ad Hoc Networks Using Signature and Certificate Revocation

A vehicular ad hoc network is a capable method of making possible road well-being, traffic supervision, as well as information distribution for driving users and travelers. One definitive objective in the blueprint of this type of network is to refuse to accept a variety of malevolent mistreatment and security assaults. The paper analyzed the existing procedure, which has covered the ways of offering security duties and conserving user solitude in the context of wireless access in vehicular environments (WAVE) applications. To make the standards more realistic, it considers techniques of certificate revocation and conditional privacy preservation. These techniques are found to be the most promising ones in vehicular ad hoc networks (VANET). Therefore, a group of narrative security methods is proposed for the safe implementation of the techniques of certificate revocation and conditional privacy preservation. For enhancement of security, the paper proposes that the message should be encapsulated with a proper certificate and be duly signed. For faster communication, we propose the use of optical wireless communication (OWC) between an onboard unit (OBU) and a roadside unit (RSU).

Research on abnormal access control of database management system under cloud computing platform

Abstract Access control is a security technique that can restrict access to protected resources, and data to only authorized users. In this paper, we design a blockchain-based access control scheme for cloud storage that is enabled by revocation. First, initialize blockchain to generate global parameters, generate complete user encryption keys and decryption keys, and perform data encryption. When the blockchain receives a user’s access request, the authorization contract determines if it is on the revocation list. If not, the key is checked. Then, it determines abnormal access and adds its identity to the revocation list, preventing further access to the database. The access control model is created by combining attribute-based encryption. After the security analysis and operational efficiency test, it can be considered that the model meets the security features, such as IND-CPA security. Regarding the time overhead of generating encryption keys, the computational overhead of this paper is the lowest, and the time required to generate encryption keys for 10 attributes is only 0.09 seconds, and for 100 attributes is only 1.62 seconds, which is better than the performance of the two attribute-based access control schemes, FIFC and AACE. The user access time overhead for 10 to 100 attributes at user encryption time is 1.38, 1.56, 1.98, 2.1, 2.53, 2.76, 3.03, 3.27, 3.66, and 3.94 seconds, respectively. The lowest decryption time consumed ensures data security and a good access experience. This study achieves fine-grained access control while protecting data privacy.

Revocable-Attribute-Based Encryption with En-DKER from Lattices

Cloud computing offers abundant computing resources and scalable storage, but data leakage in the cloud storage environment is a common and critical concern due to inadequate protection measures. Revocable-attribute-based encryption (RABE) is introduced as an advanced form of identity-based encryption (IBE), which encrypts sensitive data while providing fine-grained access control and an effective user revocation mechanism. However, most existing RABE schemes are not resistant to quantum attacks and are limited in their application scenarios due to the revocation model. In this paper, we propose a RABE scheme constructed from lattices. Our scheme has several advantages, including a near-zero periodic workload for the key generation center (KGC), ensuring scalability as the number of users increases. Additionally, the encryptor is relieved from managing a revocation list. Moreover, our scheme guarantees the confidentiality and privacy of other ciphertexts even if the decryption key for a specific period is compromised. We validated the correctness of our scheme and demonstrated its security under the assumption of learning with errors (LWE), which is widely believed to be resistant to quantum attacks. Finally, we provide an application example of our RABE scheme in the electronic healthcare scenario.

Empowering Certificate Management with Blockchain Technology

The rise of online courses and certifications has created new opportunities for individuals to enhance their skills. However, this digital transformation has also given rise to coun- terfeit certificates. To address this multifaceted issue, we present a comprehensive certificate management system founded on blockchain technology and strengthened by smart contracts. Our innovative system comprises three pivotal components: certificate generation, authenticity verification, and a user-centric digital locker for certificate storage. Blockchain technology underpins the entire system, ensuring the immutability and integrity of each certificate. The inclusion of a cryptographic hash for each certificate is a fundamental aspect of our design. Any alteration in the certificate’s data will yield a distinct hash, a powerful indicator of potential tampering. Furthermore, our system includes a secure digital locker based on cloud storage that empowers users to efficiently manage and access all their certificates in one place. Moreover, our project is committed to providing features for certificate revocation and updating, thereby enhancing the system’s flexibility and security. Hence, the blockchain and smart contract-based certificate management system offers a robust and one-stop solution to the escalating problem of counterfeit certificates in the digital era

Analysis of the Security of Internet of Multimedia Things in Wireless Environment

The Internet of Things (IoT) and real-time flexibility improve people’s lives, and IoT applications rely heavily on multimedia sensors and devices. An interconnected network of IoT multimedia devices has made the Internet of Medical Things (IoMT). It creates massive data distinct from what the Internet of Things (IoT) produced. Smart traffic monitoring and smart hospitals are only a few examples of real-time deployment applications. IoMT data and decision-making must be made quickly since it directly impacts human life. The security heterogeneity of optimization issues is a significant challenge for enabling multimedia applications on the IoT. The IoMT has difficulty achieving low-cost data collecting while maintaining data security. An Internet of Multimedia Things in a wireless environment (IoMT-WE) system decreases the bandwidth and privacy risk caused by the revocation list, ensures the integrity of batch verification information, and corresponds with Vehicular ad hoc network (VANET) security performance. The proposed method uses random subsampling and chaotic convolution to collect numerous images. The sampling method is safe since the measurement matrix is controlled by chaos. As part of the IoMT architecture, wireless multimedia sensor nodes can be more easily deployed over the long term for real-time multimedia. The Wireless Multimedia Sensor Network (WMSN) comprises nodes that can capture both multimedia and non-multimedia data. The ioMT-WE system has been tested and found to be secure and effective.

Revocation Speedrun: How the WebPKI Copes with Fraudulent Certificates

The TLS ecosystem depends on certificates to bootstrap secure connections. Certificate Authorities (CAs) are trusted to issue these correctly. However, as a result of security breaches or attacks, certificates may be issued fraudulently and need to be revoked prematurely. Revocation, as a reactive measure, is fundamentally damage control and, as such, time is critical. Therefore, measuring reaction delay is the first step to identifying how well the revocation system functions. In this paper we attempt to characterize the current performance of the WebPKI in dealing with fraudulent certificates. We present measurements of each step in the revocation process: the detection of certificate issuance through Certificate Transparency (CT) monitoring, the administrative revocation process at popular CAs, and the revocation checking behavior of end-user clients, both in a controlled virtualized environment and in the wild. We perform two live measurements, in 2022 and 2023, respectively, to provide a longitudinal comparison. We find that detection and revocation of fraudulent certificates is quick and efficient when leveraging CT and can be completed within 6.5 hours on average. Furthermore, CT is being increasingly enforced by some browsers. However, ∼83% of the clients we observed, across popular browsers, brands and OSes, completely disregard a certificate's status, whileall of the studied browsers still display soft-fail behavior, making them vulnerable to attackers capable of interfering with the network. Of the clients that do check revocation, we find that 35% can be made to accept a revoked certificate through the use of OCSP Stapling. We expect this number to grow with client-side adoption of OCSP Stapling [RFC6961]. Current OCSP expiration times allow a revoked certificate to remain fully valid for up to 7 days for the majority of CAs, exposing clients to attacks.

Capability and Blockchain-Based Fine-Grained and Flexible Access Control Model

Currently, integrating blockchain into access control systems has become a new research trend. However, existing access control systems still have problems such as easy confusion of capability authorisation subjects, inflexible capability granting and revocation, insufficient granularity of capability, insecure capability transfer and lack of capability verification. To solve these problems, this work proposes Capability- & Blockchainbased Fine-grained and Flexible Access Control (CB2FAC), defines new capability authorisation rules, and designs an authorisation tree with capability revocation list to meet the needs of flexibility and timeliness of capability revocation. Finally, simulation experiments show that CB2FAC is flexible and secure in granting, revoking, granularity control and verification of capability, and significantly outperforms the existing schemes in terms of performance.

BE-TRDSS: Blockchain-Enabled Secure and Efficient Traceable-Revocable Data-Sharing Scheme in Industrial Internet of Things

As an important component of the industrial Internet of Things (IIoT), the smart factory uses IIoT and equipment-monitoring technology to collect data to reasonably arrange production. A large number of data is collected and uploaded to the IIoT cloud platform. However, the IIoT cloud platform is semi-trusted and has structural limitations and vulnerability, which makes it necessary to realize data dynamic security sharing and malicious users tracking. In this paper, we show that most recent work on this issue is still vulnerable to security threats at first. Then a blockchain-enabled dynamic and traceable data-sharing scheme for a smart factory is proposed. Blockchain performs the user authentication and stores the ciphertext index and public keys to avoid tampering with shared data. The tracking algorithm tracks malicious users and adds them to a revocation list embedded in the ciphertext. And the authority can flexibly select domain or user revocation as required. The LSSS access policy is hidden to protect user privacy, and the cloud server uses match test algorithm to detect whether users meet hidden access policy. Additionally, online-offline encryption and outsourced decryption improve the efficiency of the scheme where the ciphertext and the pairing operations required for decryption achieve constant size. A performance analysis shows that the scheme can resist a variety of collusion attacks, and simulations show that it outperforms current schemes.

BRT: An Efficient and Scalable Blockchain-Based Revocation Transparency System for TLS Connections.

Log-based public key infrastructure(PKI) refers to a robust class of CA-attack-resilient PKI that enhance transparency and accountability in the certificate revocation and issuance process by compelling certificate authorities (CAs) to submit revocations to publicly and verifiably accessible logs. However, log-based PKIs suffer from a reliance on centralized and consistent sources of information, rendering them susceptible to split-world attacks, and they regrettably fail to provide adequate incentives for recording or monitoring CA behavior. Blockchain-based PKIs address these limitations by enabling decentralized log audits through automated financial incentives. However, they continue to face challenges in developing a scalable revocation mechanism suited for lightweight clients. In this paper, we introduce BRT, a scalable blockchain-based system for certificate and revocation transparency. It serves to log, audit, and validate the status of certificates within the transport layer security (TLS)/secure sockets layer(SSL) PKI domain. We designed an audit-on-chain framework, coupled with an off-chain storage/computation system, to enhance the efficiency of BRT when operating in a blockchain environment. By implementing a blockchain-based prototype, we demonstrate that BRT achieves storage-efficient log recording with a peak compression rate reaching 8%, cost-effective log updates for large-scale certificates, and near-instantaneous revocation checks for users.

ERSChain: Towards secure and flexible educational resource sharing using consortium blockchain and revocable ciphertext‐policy attribute‐based encryption

SummarySharing high‐quality educational resources has become an effective way to promote educational equity. The traditional educational resource sharing platforms using centralized storage architecture have security issues. Recently, many studies use blockchain to achieve secure sharing of educational resources. However, the existing blockchain‐based educational resource sharing schemes only use blockchain as a storage tool, and have issues such as low sharing efficiency, without considering copyright security, and lack of a trusted sharing environment, which prevents the large‐scale sharing of educational resources. In response, we propose ERSChain, a novel blockchain‐based educational resources sharing solution. First, we put forward a hybrid storage method that keeps the hash value of resource in the blockchain and stores the encrypted resource in the off‐chain, which can alleviate the storage and computing pressure brought by massive educational resources while ensuring the integrity of resources. Second, we construct an efficient revocable ciphertext‐policy attribute‐based encryption algorithm to implement flexible access control and an outsourced decryption algorithm to achieve greater efficiency. Obtaining access to educational resources is possible when user's attributes meet the access policy and the user's identity does not exist in the revocation list. Third, we put forward a credit mechanism to adjust the user's credibility and a credit‐based consensus mechanism to maintain the trusted sharing environment. Finally, security analysis and plentiful of experiments demonstrate that our proposed ERSChain achieves security assurance, has better applicability than similar works, and enables large‐scale sharing of educational resources.

Pengaturan Sertifikasi Halal bagi Rumah Pemotongan Hewan (RPH) di Indonesia

Halal certification is a series of processes that must be fulfilled by slaughterhouses. The aim is to provide comfort, security, safety and certainty of the availability of halal meat for the community, as well as increasing added value for business actors to produce and sell halal meat products. This research examines the provisions regarding halal certification rules for slaughterhouses in Indonesia, the halal certification mechanism and the consequences for slaughterhouses that are not halal certified. The research method used is the normative juridical method, namely research that focuses on legal norms contained in statutory regulations. The research results show that the provisions for halal certification for slaughterhouses in Indonesia are regulated in Law Number 33 of 2014 concerning Halal Product Guarantees, Law Number 6 of 2023 concerning Determination of Government Regulations in Lieu of Law Number 2 of 2022 concerning Job Creation, Government Regulation Number 39 of 2021 concerning the Implementation of the Halal Product Guarantee Sector, Decree of the Minister of Religion Number 748 of 2021 concerning Types of Products that must be halal certified, and detailed guidelines are regulated in the Decree of the Head of the Halal Product Guarantee Organizing Agency Number 77 of 2023 concerning Guidelines for Implementing the Product Guarantee System Halal in Slaughtering Ruminants and Poultry. The halal certification mechanism consists of the manager or business operator of the slaughterhouse registering and attaching the required documents; BPJPH will examine the requirements that have been attached; Next, an audit and inspection of the product will be carried out, submitting the inspection results to the MUI for a fatwa to be issued; and issue a halal certificate if it passes the audit. The consequences for slaughterhouses that do not implement halal product guarantees are that they will receive administrative sanctions in the form of reprimands, written warnings and revocation of halal certificates for those who already have halal certificates. The author suggests that these consequences be added in the form of slaughterhouses that do not have a halal certificate not being allowed to operate and slaughtered meat being prohibited from circulating.

BENIGREEN: Blockchain-Based Energy-Efficient Privacy-Preserving Scheme for Green IoT

The energy conservative extension of Internet-of-Thing (IoT), green IoT, is a revolutionary approach in connecting people, processes, and things in an energy-efficient way. The existing research works in the domain of green IoTs forbid the use of decentralized management (e.g., blockchain) of data due to its intrinsic disadvantages of block mining, transaction incentives, and less throughput. However, the advantages of blockchains urge the development of new decentralized strategies utilizing the architecture of green IoTs. The infancy stage of the conjunction between green IoTs and blockchains, the need of decentralization in energy management in green IoTs motivate us for the present research. In this paper, we address the problems of decentralization, energy-conservation, and privacy simultaneously. We introduce the first blockchain-based privacy-preserving framework for green IoTs. We name this framework as "Blockchain-based ENergy-efficient and prIvacy-preserving data management scheme for GREEN-iot (BENIGREEN)" for smart cities. BENIGREEN uses weight metrics for energy-efficient cluster heads selection. The use of weight metrics is a novel contribution in the field of green IoTs. Further, we integrate a decentralized blockchain framework with an authentication scheme for secure transmission among Base Station (BS) and sensor nodes by employing registration, certification, and revocation phases. Consequently, BS allocates the collected information from cluster heads to decentralized blockchain and cloud storage. The BS eliminates all malicious nodes from the network by employing a certificate revocation process. We execute thorough experiments in terms of the operation time, throughput, average energy consumption, and computational latency. The comparative analysis with the state-of-the-art schemes show that BENIGREEN is efficient for IoT paradigm.

Revocable Signature Scheme with Implicit and Explicit Certificates.

This paper addresses the certificate revocation problem and proposes the first revocable pairing-based signature scheme with implicit and explicit certificates (IE-RCBS-kCAA). We should no longer discuss whether to revoke certificates but how to do it effectively, ensuring both the scalability of the revocation operation and the non-repudiation of the signature in the short or long term. Under the computational difficulty assumptions of the modified collusion attack algorithm with k traitors (k-mCAA) and discrete logarithm (DL) problems, we demonstrate that our scheme is secure against existential unforgeability under chosen message attacks (EUF-IERCBS-kCAA-CMA) in a random oracle model. The proposed solution is scaled and allows the use of many trusted status authorities that issue explicit short-term certificates confirming the validity of explicit long-term certificates. Furthermore, we demonstrate that our signature scheme has a short-term non-repudiation property for the shell validity model.