Timed-release Encryption Research Articles

Multiple time servers timed-release encryption based on Shamir secret sharing for EHR cloud system

Electronic health record (EHR) cloud system, as a primary tool driving the informatization of medical data, have positively impacted both doctors and patients by providing accurate and complete patient information. However, ensuring the security of EHR cloud system remains a critical issue. Some patients require regular remote medical services, and controlling access to medical data involving patient privacy during specific times is essential. Timed-release encryption (TRE) technology enables the sender to preset a future time T at which the data can be decrypted and accessed. It is a cryptographic primitive with time-dependent properties. Currently, mainstream TRE schemes are based on non-interactive single time server methods. However, if the single time server is attacked or corrupted, it is easy to directly threaten the security applications of TRE. Although some research schemes “distribute” the single time server into multiple ones, they still cannot resist the single point of failure problem. To address this issue, we propose a multiple time servers TRE scheme based on Shamir secret sharing and another variant derived from it. In our proposed schemes, the data receiver does not need to interact with the time servers; instead, they only need to obtain the time trapdoors that exceed or equal the preset threshold value for decryption, which ensures the identity privacy of the data sender and tolerates partial downtime or other failures of some time servers, significantly improving TRE reliability. Security analysis indicates that our proposed schemes demonstrate data confidentiality, verifiability, anti-advance decryption, and robust decryption with multiple time trapdoors, making them more practical. Efficiency analysis indicates that although our schemes have slightly higher computational costs than most efficient existing TRE schemes, such differences are insignificant from a practical application perspective.

Timed-release encryption anonymous interaction protocol based on smart contract

Timed-release encryption (TRE) is a cryptographic primitive that can control the decryption time and has significant application value in time-sensitive scenarios. To solve the reliability issue of nodes in existing TRE anonymous interaction schemes, we propose a blockchain-based TRE protocol for anonymous query time trapdoors. In our protocol, the recipient divides the encrypted trapdoor request information into n ciphertext fragments using secret sharing technology near the decryption time, and employs the idea of onion routing to perform layer-by-layer encryption, creating onion-type data transmitted through middlemen selected from the smart contract. After receiving the ciphertext fragments, the time server integrates them to obtain the trapdoor request information and returns the corresponding time trapdoor to the recipient. This allows the recipient to query any time trapdoor anonymously. Our protocol provides a normative design for the smart contract and specific constraints on the participants’ behavior. Compared with the related anonymous query trapdoor schemes, our protocol improves the probability of successful queries. Security analysis shows that our protocol can resist release-ahead attack, interruption attack, eavesdropping attack, and replacement attack. Performance analysis shows that our protocol outperforms related protocols regarding anonymity, efficiency, and flexibility, achieving highly efficient anonymous interactions. Finally, we conducted an experiment in the Ethereum Rinkeby test network. For the settings of ciphertext fragment number n=3 and ciphertext fragment threshold t=2, the gas consumption for a user to execute the contract was $5.66, which was higher than the contract cost of related schemes, but the contract execution cost was within an acceptable range.

A tamper-resistant timed secure data transmission protocol based on smart contract

Many time-sensitive scenarios need to decrypt data at a specified time. The timed-release encryption (TRE) primitive can meet this requirement. However, in the single-time server TRE model, there is a single point of failure problem. Therefore, we propose a tamper-resistant timed secure data transmission protocol based on smart contracts. Firstly, by decomposing the ciphertext into ciphertext fragments, the amount of deposit that a single middleman needs to submit is reduced. Secondly, it provides the system with security redundancy that changes with the decomposition mode. Thirdly, the sender is required to submit the hash value of each ciphertext fragment to the blockchain network at the same time as sending data, so that the receiver can quickly verify the authenticity of the ciphertext to resist substitution attack. Security analysis shows that the proposed protocol model can resist interruption attacks, release-ahead attacks and replacement attacks. Finally, we conduct a monetary cost test on the Ethereum’s Rinkeby test network. The results show that our running cost is almost double compared with the existing similar scheme, but it is still very low and almost negligible compared with the value of the content and the expected profits it brings.

A Privacy Protection Scheme for Bidding Users of Peer-to-Peer Electricity Call Auction Trading in Microgrids

Renewable energy generation is greatly affected by the weather, and electricity is not easily stored in large quantities. So, the call auction trading based on the rule of the maximum trading volume is of great significance to promote the electricity consumption of microgrids. Therefore, in microgrid electricity call auction trading, aiming at the problems, such as bidding messages may leak users’ privacy, they may also be eavesdropped or tampered with in the bidding process, and the balance between privacy protection and supervision cannot be achieved, a privacy protection scheme for bidding users of peer-to-peer electricity call auction trading in microgrids is proposed. It consists of a market layer and a blockchain layer. Based on the improved certificateless ring signcryption and timed-release encryption algorithms, the market layer is used to hide the user's real identity while encrypting the bidding message and track illegal users. The blockchain layer is used for trading settlement and trading record storage to ensure data storage security. The security is proved theoretically. Performance analysis and simulation results indicate that computational and communication costs are low. Especially the verification cost is low and increases slowly with the increase in the number of ring members.

A Lightweight and Privacy-Preserving Answer Collection Scheme for Mobile Crowdsourcing

Mobile Crowdsourcing (MCS) has become an emerging paradigm evolved from crowdsourcing by employing advanced features of mobile devices such as smartphones to perform more complicated, especially spatial tasks. One of the key procedures in MCS is to collect answers from mobile users (workers), which may face several security issues. First, authentication is required to ensure that answers are from authorized workers. In addition, MCS tasks are usually location-dependent, so the collected answers could disclose workers'' location privacy, which may discourage workers to participate in the tasks. Finally, the overhead occurred by authentication and privacy protection should be minimized since mobile devices are resource-constrained. Considering all the above concerns, in this paper, we propose a lightweight and privacy-preserving answer collection scheme for MCS. In the proposed scheme, we achieve anonymous authentication based on traceable ring signature, which provides authentication, anonymity, as well as traceability by enabling malicious workers tracing. In order to balance user location privacy and data availability, we propose a new concept named current location privacy, which means the location of the worker cannot be disclosed to anyone until a specified time. Since the leakage of current location will seriously threaten workers'' personal safety, causing such as absence or presence disclosure attacks, it is necessary to pay attention to the current location privacy of workers in MCS. We encrypt the collected answers based on timed-release encryption, ensuring the secure transmission and high availability of data, as well as preserving the current location privacy of workers. Finally, we analyze the security and performance of the proposed scheme. The experimental results show that the computation costs of a worker depend on the number of ring signature members, which indicates the flexibility for a worker to choose an appropriate size of the group under considerations of privacy and efficiency.

Anonymous Auction Protocol Based on Timed-Release Encryption Atop Consortium Blockchain

Anonymous Auction Protocol Based on Timed-Release Encryption Atop Consortium Blockchain

Provably Secure Security-Enhanced Timed-Release Encryption in the Random Oracle Model

Cryptographic primitive of timed-release encryption (TRE) enables the sender to encrypt a message which only allows the designated receiver to decrypt after a designated time. Combined with other encryption technologies, TRE technology is applied to a variety of scenarios, including regularly posting on the social network and online sealed bidding. Nowadays, in order to control the decryption time while maintaining anonymity of user identities, most TRE solutions adopt a noninteractive time server mode to periodically broadcast time trapdoors, but because these time trapdoors are generated with fixed time server’s private key, many “ciphertexts” related to the time server’s private key that can be cryptanalyzed are generated, which poses a big challenge to the confidentiality of the time server’s private key. To work this out, we propose a concrete scheme and a generic scheme of security-enhanced TRE (SETRE) in the random oracle model. In our SETRE schemes, we use fixed and variable random numbers together as the time server’s private key to generate the time trapdoors. We formalize the definition of SETRE and give a provably secure concrete construction of SETRE. According to our experiment, the concrete scheme we proposed reduces the computational cost by about 10.8% compared to the most efficient solution in the random oracle model but only increases the almost negligible storage space. Meanwhile, it realizes one-time pad for the time trapdoor. To a large extent, this increases the security of the time server’s private key. Therefore, our work enhances the security and efficiency of the TRE.

TAFC: Time and Attribute Factors Combined Access Control for Time-Sensitive Data in Public Cloud

The new paradigm of outsourcing data to the cloud is a double-edged sword. On the one hand, it frees data owners from the technical management, and is easier for data owners to share their data with intended users. On the other hand, it poses new challenges on privacy and security protection. To protect data confidentiality against the honest-but-curious cloud service provider, numerous works have been proposed to support fine-grained data access control. However, till now, no schemes can support both fine-grained access control and time-sensitive data publishing. In this paper, by embedding timed-release encryption into Ciphertext-Policy Attribute-based Encryption (CP-ABE), we propose a new time and attribute factors combined access control on time-sensitive data for public cloud storage (named TAFC). Based on the proposed scheme, we further propose an efficient approach to design access policies faced with diverse access requirements for time-sensitive data. Extensive security and performance analysis shows that our proposed scheme is highly efficient and satisfies the security requirements for time-sensitive data storage in public cloud.

Self-updatable encryption: Time constrained access control with hidden attributes and better efficiency

Revocation and key evolving paradigms are central issues in cryptography, and in PKI in particular. A novel concern related to these areas was raised in the recent work of Sahai, Seyalioglu, and Waters (CRYPTO 2012) who noticed that revoking past keys should at times (e.g., the scenario of cloud storage) be accompanied by revocation of past ciphertexts (to prevent unread ciphertexts from being read by revoked users). They introduced revocable-storage attribute-based encryption (RS-ABE) as a good access control mechanism for cloud storage. RS-ABE protects against the revoked users not only the future data by supporting key-revocation but also the past data by supporting ciphertext-update, through which a ciphertext at time T can be updated to a new ciphertext at time T+1using only the public key. Motivated by this pioneering work, we ask whether it is possible to have a modular approach, which includes a primitive for time managed ciphertext update as a primitive. We call encryption which supports this primitive a “self-updatable encryption” (SUE). We then suggest a modular cryptosystems design methodology based on three sub-components: a primary encryption scheme, a key-revocation mechanism, and a time-evolution mechanism which controls the ciphertext self-updating via an SUE method, coordinated with the revocation (when needed). Our goal in this is to allow the self-updating ciphertext component to take part in the design of new and improved cryptosystems and protocols in a flexible fashion. Specifically, we achieve the following results:We first introduce a new cryptographic primitive called self-updatable encryption (SUE), realizing a time-evolution mechanism. In SUE, a ciphertext and a private key are associated with time. A user can decrypt a ciphertext if its time is earlier than that of his private key. Additionally, anyone (e.g., a cloud server) can update the ciphertext to a ciphertext with a newer time. We also construct an SUE scheme and prove its full security under static assumptions. Following our modular approach, we present a new RS-ABE scheme with shorter ciphertexts than that of Sahai et al. and prove its security. The length efficiency is mainly due to our SUE scheme and the underlying modularity. We apply our approach to predicate encryption (PE) supporting attribute-hiding property, and obtain a revocable-storage PE (RS-PE) scheme that is selectively-secure. We further demonstrate that SUE is of independent interest, by showing it can be used for timed-release encryption (and its applications), and for augmenting key-insulated encryption with forward-secure storage.

Revocable Quantum Timed-Release Encryption

Timed-release encryption is a kind of encryption scheme in which a recipient can decrypt only after a specified amount of time T (assuming that we have a moderately precise estimate of his computing power). A revocable timed-release encryption is one where, before the time T is over, the sender can “give back” the timed-release encryption, provably loosing all access to the data. We show that revocable timed-release encryption without trusted parties is possible using quantum cryptography (while trivially impossible classically). Along the way, we develop two proof techniques in the quantum random oracle model that we believe may have applications also for other protocols. Finally, we also develop another new primitive, unknown recipient encryption , which allows us to send a message to an unknown/unspecified recipient over an insecure network in such a way that at most one recipient will get the message.

Timed-Release Certificateless Encryption

Timed-Release Encryption(TRE) is an encryption mechanism that allows a receiver to decrypt a ciphertext only after the time that a sender designates. In this paper, we propose the notion of Timed-Release Certificateless Encryption(TRCLE), and define its security models. We also show a generic con-struction of TRCLE from Public-Key Encryption(PKE), Identity-Based Encryption(IBE) and one-time signature, and prove that the constructed scheme achieves the security we defined.

A full lifecycle privacy protection scheme for sensitive data in cloud computing

With the rapid development of versatile cloud services, it becomes increasingly susceptible to expose users’ sensitive data into the cloud computing environment. In this paper, we propose a full lifecycle privacy protection scheme for sensitive data (FullPP), which is based on identity-based timed-release encryption (ID-TRE) algorithm and distributed hash table (DHT) network. In the FullPP scheme, we first encrypt the sensitive data into a ciphertext, which is broken up into extracted ciphertext and encapsulated ciphertext by using an extracting algorithm. Then, we leverage the ID-TRE algorithm to encrypt the decryption key and combine the key’s ciphertext with the extracted ciphertext to generate ciphertext shares. Finally, we distribute the ciphertext shares into the DHT network and store the encapsulated ciphertext into cloud servers. To recover the plaintext of the sensitive data, sufficient ciphertext shares, ID-TRE private key and the encapsulated ciphertext should be obtained during the lifecycle of the sensitive data. As a result, FullPP is able to provide full lifecycle privacy protection for users’ sensitive data by making it unreadable before a predefined time and automatically destructed after expiration. Security analysis indicates that the FullPP scheme is able to resist against both traditional attacks on the cloud servers and Sybil attacks on the DHT network. Experiment result shows that the FullPP scheme proposed by us is more effective and efficient than other existing schemes.

From Ephemerizer to Timed-Ephemerizer: Achieve Assured Lifecycle Enforcement for Sensitive Data

The concept of Ephemerizer, proposed by Perlman, is a cryptographic primitive for assured data deletion. With an Ephemerizer protocol, data in persistent storage devices will always be encrypted simultaneously using an ephemeral public key of the Ephemerizer (an entity which will publish a set of ephemeral public keys and periodically delete the expired ones) and the long-term public key of a user. An Ephemerizer protocol enables the user to securely decrypt the encrypted data without leaking any information to the Ephemerizer. So far, no security model has ever been proposed for this primitive and existing protocols have not been studied formally. Not surprisingly, we show that some existing Ephemerizer protocols possess security vulnerabilities. In this paper, we introduce the notion of Timed-Ephemerizer, which can be regarded as a hybrid primitive by combining Ephemerizer and Timed-Release Encryption. Compared with an Ephemerizer protocol, a Timed-Ephemerizer protocol further guarantees that data will only be released after a pre-defined disclosure time. Moreover, we propose a security model for Timed-Ephemerizer and formalize relevant security properties. We also propose a new Timed-Ephemerizer protocol and prove its security in the security model.

Timed-Release Hierarchical Identity-Based Encryption

We propose a notion of hierarchical identity-based encryption (HIBE) scheme with timed-release encryption (TRE) mechanism, timed-release hierarchical identity-based encryption (TRHIBE), and define its security models. We also show a generic construction of TRHIBE from HIBE and one-time signature, and discuss the security of the constructed scheme.

Privacy-aware event data recorders: cryptography meets the automotive industry again

Vehicles are equipped with more technology with each passing day. Acronyms such as ABS (anti-lock braking system), EBD (electronic brakeforce distribution) or EPS (electric power steering) have become commonplace, and are used as synonyms for safety and comfort. On the contrary, others like EDR (event data recorder) are not as popular. EDR, commonly known as automotive black boxes, are devices used to collect data about a vehicle and its occupants, which can be accessed after an accident to clarify its cause. With the upcoming regulation of the National Highway Traffic Safety Administration requiring manufacturers to include EDR in all new vehicles, privacy advocates have raised some alarms related to the storage of and access to these data. In this article, we propose a novel privacy-aware solution for the EDR of modern vehicles. Our solution is based on modern cryptographic primitives like timed release encryption (TRE), and it guarantees the privacy of the vehicle's occupants while allowing the full functionality of EDR in case of emergency.

Self-sustaining, efficient and forward-secure cryptographic constructions for Unattended Wireless Sensor Networks

Unattended Wireless Sensor Networks (UWSNs) operating in hostile environments face great security and performance challenges due to the lack of continuous real-time communication with the final data receivers (e.g., mobile data collectors). The lack of real-time communication forces sensors to accumulate sensed data possibly for long time periods, along with the corresponding authentication tags. It also makes UWSNs vulnerable to active adversaries, which can compromise sensors and manipulate the collected data. Hence, it is critical to have forward security property such that even if the adversary can compromise the current keying materials, she cannot forge authentication tags generated before the compromise. Forward secure and aggregate signature schemes are developed to address these issues. Unfortunately, existing schemes either impose substantial overhead, or do not allow public verifiability, thereby impractical for resource-constrained UWSNs.In this paper, we propose a new class of cryptographic schemes, referred to as Hash-BasedSequentialAggregate andForwardSecureSignature (HaSAFSS), which allows a signer to sequentially generate a compact, fixed-size, and publicly verifiable signature efficiently. We develop three HaSAFSS schemes, Symmetric HaSAFSS (Sym-HaSAFSS), Elliptic Curve Cryptography (ECC) based HaSAFSS (ECC-HaSAFSS) and self-SUstaining HaSAFSS (SU-HaSAFSS). These schemes integrate the efficiency of MAC-based aggregate signatures and the public verifiability of Public Key Cryptography (PKC)-based signatures by preserving forward security via Timed-Release Encryption (TRE). We demonstrate that our schemes are secure and also significantly more efficient than previous approaches.

A Timed-Release Proxy Re-Encryption Scheme

Timed-Release Encryption (TRE) is a kind of time-dependent encryption, where the time of decryption can be controlled. More precisely, TRE prevents even a legitimate recipient decrypting a ciphertext before a semi-trusted Time Server (TS) sends trapdoor sT assigned with a release time T of the encryptor's choice. Cathalo et al. (ICICS2005) and Chalkias et al. (ESORICS2007) have already considered encrypting a message intended for multiple recipients with the same release time. One drawback of these schemes is the ciphertext size and computational complexity, which depend on the number of recipients N. Ideally, it is desirable that any factor (ciphertext size, computational complexity of encryption/decryption, and public/secret key size) does not depend on N. In this paper, to achieve TRE with such fully constant costs from the encryptor's/decryptor's point of view, by borrowing the technique of Proxy Re-Encryption (PRE), we propose a cryptosystem in which even if the proxy transformation is applied to a TRE ciphertext, the release time is still effective. By sending a TRE ciphertext to the proxy, an encryptor can foist N-dependent computation costs on the proxy. We call this cryptosystem Timed-Release PRE (TR-PRE). This function can be applied to efficient multicast communication with a release time indication.

Oblivious transfer with timed-release receiver’s privacy

Abstract Oblivious transfer (OT) is an important primitive used in many cryptographic protocols. According to the traditional OT’s security requirements, the privacy of the receiver is protected forever, which, however, limits the applications of OT in some areas. In this paper, we propose a new OT with timed-release receiver’s privacy in which the sender has N messages, of which the receiver can choose to receive one or more, in such a way that (a) the receiver only learns about the requested messages, and (b) the sender learns the receiver’s selections after a designated time. Thus the receiver’s privacy is just protected within a period of time. Besides, we also present a concrete scheme combining Tzeng’s OT scheme with Casassa Mont et al.’s timed-release encryption scheme.

Flexible Timed-Release Encryption

This paper presents a new scheme for Timed-Release Encryption (TRE), which is mainly designed for global use. TRE aims to control the timing of disclosing information. The major approach to TRE assumes that any participants can receive a time token broadcasted by a trusted agent, called a time server. Our scheme is based on this approach and allows participants to generate an encrypted message that can be decrypted using designated or any authenticated time servers including even those which are authenticated after encryption. In this sense, our scheme has a more flexible framework in terms of message decryption.

Provably Secure Timed-Release Public Key Encryption

A timed-release cryptosystem allows a sender to encrypt a message so that only the intended recipient can read it only after a specified time. We formalize the concept of a secure timed-release public-key cryptosystem and show that, if a third party is relied upon to guarantee decryption after the specified date, this concept is equivalent to identity-based encryption; this explains the observation that all known constructions use identity-based encryption to achieve timed-release security. We then give several provably-secure constructions of timed-release encryption: a generic scheme based on any identity-based encryption scheme, and two more efficient schemes based on the existence of cryptographically admissible bilinear mappings. The first of these is essentially as efficient as the Boneh-Franklin Identity-Based encryption scheme, and is provably secure and authenticated in the random oracle model; the final scheme is not authenticated but is provably secure in the standard model (i.e., without random oracles).