Time-stamping Service Research Articles

IoETTS: A Decentralized Blockchain-based Trusted Time-stamping Scheme for Internet of Energy

<p>As a new-style smart grid, Internet of Energy (IoE) is important and how to provide its trusted time-stamping service becomes a hit. For example, an energy provider needs to prove he/she transferred some energy to a consumer at some time. Nevertheless, traditional trusted time-stamping scheme with a central service provider is not suitable for IoE. Some researchers try to solve this problem via blockchain, due to its decentralization, traceability and tamper-proof. However, there are still chal­lenges when using blockchain. Some have to introduce another kind of central participant. Some have to face the problem of accuracy and availability when using the Bitcoin blockchain. Some have to generate too many extra transactions. To address the aforementioned problems, we propose a fully decentralized trusted time-stamping scheme without any central participant and fulfill six design goals. Compared with the state-of-the-art blockchain-based time-stamping scheme named Chronos, our scheme enjoys less cryptographic operations. We then tested our scheme in the development (local) network and two live networks of the Ethereum. The experiment shows that we have implemented a simple, effective, accurate and low-cost decentralized trusted time-stamping scheme.</p> <p> </p>

Reviewing the ISO/IEC Standard for Timestamping Services

Timestamping services are used to prove that a data item existed at a given point in time. This proof is represented by a timestamp token that is created by a timestamping authority. ISO/ IEC 18014 specifies timestamping services and requires them to hold the following two properties: (1) The data being timestamped is not disclosed to the timestamping authority; hash values of the data are provided to the authority instead. (2) A timestamp token can be renewed; as a result, the validity duration of a timestamp token is not restricted by the lifetimes of underlying algorithms or policies. In this article, we review this standard and discover several issues: Due to inconsistent writing or information missing, a timestamping service following the standard specification may not be able to achieve these designed properties. We provide a solution to each issue.

Accurate and decentralized timestamping using smart contracts on the Ethereum blockchain

Timestamps allow us to identify a date and time when a piece of data existed or an event took place. For example, we use timestamps to establish the date when we grant a patent. Services that offer trusted timestamps on the blockchain exist, where one creates a timestamp on a value by sending the blockchain a transaction containing the value, which is eventually confirmed in a block a miner creates and timestamps. Our work focuses on the accuracy of such timestamps created on the Ethereum blockchain. We estimate that their mean accuracy is half of the average time between consecutive blocks. However, Ethereum clients geth and parity allow accuracy to vary in up to a few tens of seconds. Surprisingly, we found out empirically that miners can backdate data using the timestamp on a block, which is a serious flaw in timestamping services. To address this problem, we propose a new decentralized timestamping service that combines smart contracts and distinct time providers. The service offers timestamps with higher accuracy of milliseconds. We conduct a cost analysis of our service, which shows that Ethereum transaction fees drive our timestamps costs when the service scales up. Finally, we discuss alternatives to cut costs.

Misbehavior in Bitcoin

Bitcoin is a decentralized payment system that relies on Proof-of-Work (PoW) to resist double-spending through a distributed timestamping service. To ensure the operation and security of Bitcoin, it is essential that all transactions and their order of execution are available to all Bitcoin users. Unavoidably, in such a setting, the security of transactions comes at odds with transaction privacy. Motivated by the fact that transaction confirmation in Bitcoin requires tens of minutes, we analyze the conditions for performing successful double-spending attacks against fast payments in Bitcoin, where the time between the exchange of currency and goods is short (in the order of a minute). We show that unless new detection techniques are integrated in the Bitcoin implementation, double-spending attacks on fast payments succeed with considerable probability and can be mounted at low cost. We propose a new and lightweight countermeasure that enables the detection of double-spending attacks in fast transactions. In light of such misbehavior, accountability becomes crucial. We show that in the specific case of Bitcoin, accountability complements privacy. To illustrate this tension, we provide accountability and privacy definition for Bitcoin, and we investigate analytically and empirically the privacy and accountability provisions in Bitcoin.

DNStamp: Short-lived trusted timestamping

Trusted timestamping consists in proving that certain data existed at a particular point in time. Existing timestamping methods require either a centralized and dedicated trusted service or the collaboration of other participants using the timestamping service.We propose a novel trusted timestamping scheme, called DNStamp, that does not require a dedicated service nor collaboration between participants. DNStamp produces short-lived timestamps with a validity period of several days. The generation and verification involves a large number of Domain Name System cache resolvers, thus removing any single point of failure and any single point of trust. Any host with Internet access may request or verify a timestamp, with no need to register to any timestamping service. We provide a full description and analysis of DNStamp. We analyze the security against various adversaries and show resistance to forward-dating, back-dating and erasure attacks. Experiments with our implementation of DNStamp show that one can set and then reliably verify timestamps even under continuous attack conditions.

Implementation of a Timestamping Service for SunSPOT Sensors

Recent technological advances have enabled the development of sensing platforms that include different types of sensors, and integrate several components such as memory, processor, and radio. Time synchronization is a critical service for a wide range of applications in wireless sensor networks. Through this service, the sensors in the network are able to coordinate and carry out sensing processes in a way that permits the correct ordering of the global events, and save energy. The protocols that provide better accuracy rely on a timestamping mechanism which allows them to eliminate several sources of error in the time synchronization process. However, in newer platforms, such as SunSPOT, no timestamping mechanism is provided. In this paper, we present an implementation of a microsecond accuracy timestamping service in the SunSPOT platform, which provides the foundation for the implementation of accurate time synchronization protocols in a wireless SunSPOT sensor network.

Security of the design of time-stamped signatures

To ensure integrity and originality of digital information, digital signatures were proposed to provide both authority and non-repudiation. However, without an authenticated time-stamp, we can neither trust signed documents when the signers' signature key was lost, stolen, or accidentally compromised, nor solve the cases when the signer himself repudiates the signing, claiming that has accidentally lost his signature key. To withstand forward forgery suffered by linking schemes and to reduce verification cost, Sun et al. proposed four time-stamped signature schemes that are based on absolute temporal authentication. Though Sun et al. claimed that these schemes are quite secure against the forward forgery, we find that they suffered from substitution attacks, by which the signer can backward/forward forge signatures and the time-stamping service can also forge signatures. Finally, we also propose four time-stamped signature schemes to overcome these security flaws. Moreover, the proposed new schemes are more efficient than the Sun et al. schemes.

Efficient Key-Evolving Protocol for the GQ Signature *

Several key-evolving protocols for the Guillou-Quisquater (GQ) signature have been proposed. However, the computational loads are still high, which require the multiplication of several modular exponentiations of at least 1024-bit length. In this paper, we present a low-complexity key-evolving protocol with two additional benefits. First, it ensures the secrecy of other signing keys, even when the signing keys in some periods are compromised. Second, it provides the basic time-stamping service, which is important for legal or notary applications. Related schemes are also compared with our scheme.

On the design of time-stamped signatures

To ensure integrity and originality of digital information, digital signatures were proposed to provide both authority and non-repudiation. However, without an authenticated time-stamp we can neither trust signed documents when the signer's signature key was lost, stolen, or accidentally compromised, nor solve the cases when the signer himself repudiates the signing, claiming that he has accidentally lost his signature key. Based on relative temporal authentication, several linking schemes for digital time-stamping have been proposed to solve this problem. However, these schemes suffer from the forward forgery which is an attempt to stamp a present time-stamp on a past document by an unauthorized one. In addition, the verification cost in these schemes is too high because it is dependent upon the number of the issued time-stamps. In this paper, we propose four time-stamped signature schemes that are based on absolute temporal authentication. These proposed schemes are very efficient in verifying the validity of time-stamped signatures and are quite secure against the forward forgery. It is natural that the time-stamped signature schemes based on absolute temporal authentication suffer from the weakness when the signer colludes with the Time-Stamping Service. To combat the collusion problem, time-stamped signature schemes with hybrid temporal authentication are therefore proposed.

A new family of authentication protocols

We present a related family of authentication and digital signature protocols based on symmetric cryptographic primitives which perform substantially better than previous constructions. Previously, one-time digital signatures based on hash functions involved hundreds of hash function computations for each signature; we show that given online access to a timestamping service, we can sign messages using only two computations of a hash function. Previously, techniques to sign infinite streams involved one such one-time signature for each message block; we show that in many realistic scenarios a small number of hash function computations is sufficient. Previously, the Diffie Hellman protocol enabled two principals to create a confidentiality key from scratch: we provide an equivalent protocol for integrity, which enables two people who do not share a secret to set up a securely serialised channel into which attackers cannot subsequently intrude. In addition to being of potential use in real applications, our constructions also raise interesting questions about the definition of a digital signature, and the relationship between integrity and authenticity.

How to time-stamp a digital document

The prospect of a world in which all text, audio, picture, and video documents are in digital form on easily modifiable media raises the issue of how to certify when a document was created or last changed. The problem is to time-stamp the data, not the medium. We propose computationally practical procedures for digital time-stamping of such documents so that it is infeasible for a user either to back-date or to forward-date his document, even with the collusion of a time-stamping service. Our procedures maintain complete privacy of the documents themselves, and require no record-keeping by the time-stamping service.