Unlike conventional blockchains, which have a sequential model and restrictive participation rules, DAG-based blockchains offer a flexible structure for enabling concurrency. When all nodes participate actively, the concurrency in block generation naturally creates conflicting branches. Corrective approaches often discard valid blocks to solve conflicts, leading to resource wastage. In preventive approaches, transactions are even separated into groups for parallel processing, complicating transaction processing with outcomes reconciliation, workload balancing, and correctness challenges. This last incurs high communication costs and high confirmation delays. To leverage the whole participant’s capacity to process transaction, the asynchrony in participation and concurrency in block creation must be preserved by resolving the conflicts without arbitrarily wasting resources. This paper introduces a new corrective approach in DAG-based blockchain that identifies discrepancies between conflicting blocks. These differences are classified into concurrency patterns which are useful for resolving conflicts among concurrent blocks maintaining the asynchrony of the system and without discarding, or reversing transactions.

Collaborative Cyber-Physical Systems (CCPSs) have gained prominence in Intelligent Transport Systems, Monitoring Epidemic Spreading, and the Industrial Internet of Things. The devices in CCPSs interact with the environment through sensors and actuators. Additionally, these devices collaborate to achieve a specific task. This collaboration and interaction introduces a new set of challenges related to spatio-temporal constraints and dependencies. Therefore, there is a growing need to understand the inherent spatio-temporal behaviors in CCPSs, as well as to identify and model them effectively. In this paper, we present a comprehensive study that focuses on the identification, characterization, and classification of spatio-temporal phenomena observed in social insect societies. By drawing parallels between the spatio-temporal behaviors exhibited by social insects and those prevalent in Collaborate Cyber-Physical Systems, we assert that similar dynamics can be leveraged to design innovative solutions that are more efficient and effective.

As a decentralized system, Bitcoin has earned its reputation as a reliable and secure method for online payments, eliminating the need for a trusted third party. It supports a range of transaction types, such as Multisig, Pay-to-PubKey (P2PK), Pay-to-Script-Hash (P2SH), Pay-to-Public-Key-Hash (P2PKH), SegWit, and Coinbase. These transactions are designed to meet specific user needs, such as throughput and security. For example, the SegWit method modifies the transaction structure and increases the block size to enhance throughput. Similarly, P2PKH reinforces the security of transactions by covering the public key until the funds are used. However, these changes directly affect the growth of blockchain storage, which is one of the main challenges for Bitcoin's adoption. To the authors' knowledge, we found no comparative studies on storage costs between transaction types. To bridge this gap, this paper presents an exhaustive analysis of the storage used by these Bitcoin transaction types. We analyzed 845 million transactions and found that transaction types such as P2SH and SegWit have reduced storage efficiency. This study paves the way for future research to achieve scalable storage solutions in Bitcoin.

Multi-domain federations support shared network services. Many orchestrators manage the service’s lifecycle. For the shared VNF Forwarding Graph (VNF-FG) reconfiguration, orchestrators update the graph’s logical information, ensuring a consistent behavior for replicas. Only one work in the literature considers sharing the VNF-FG. However, it offers weak consistency guarantees, without considering the VNF-FG’s non-functional dependencies. In case of a conflict, while updating the VNF-FG, the orchestrators solve consensus. However, this adds latency, undermining the goal of Network Function Virtualization. This paper introduces the first coordination-free multi-domain orchestration algorithm for consistent shared VNF-FG reconfiguration. Unlike the current state of the art, the proposed algorithm skips the coordination phase, offers strong eventual consistency, and supports non-functional dependencies. We present two variants: the preventive, where transient inconsistent states are prevented; the corrective, where intermediary inconsistent states, during the updating process, are tolerated. We prove the correctness of our algorithm and evaluate it. The variants, unlike the state of the art, reconfigure consistently the shared VNF-FGs without solving consensus. They offer stronger guarantees compared to the literature, like allowing orchestrators to reject ongoing reconfigurations without a high impact on performance.

Network Function Virtualization (NFV) enables running Virtualized Network Functions (VNF) on top of any generic, commercial off-the-shelf hardware. VNFs rely on the VNF-Forwarding Graph (VNF-FG) concept to describe and implement network topologies. VNF-FGs are provisioned and managed by appropriate orchestrators. In the multidomain approach, and for complex and sophisticated network topologies, VNF-FGs are managed by multiple orchestrators. Despite being a key task in the lifecycle of network services, the reconfiguration of VNF-FGs under multi-domain orchestration has not been thoroughly explored in the literature, focused mostly on the initial VNF-FG placement and embedding. Reconfiguration enables the providers to answer to unforeseen changes in the environment. However, such distributed orchestration might lead to inconsistencies, and thus partial or total failure of network services. In turn, such inconsistencies increase the cost for providers. This paper proposes the use of causal dependencies among orchestrators to provision consistent VNF-FG reconfiguration in distributed multi-domain environments under asynchronous communication channels. The proposed model is implemented and compared with the current ETSI VNF-FG reconfiguration algorithm. Results indicate that, with this proposal, the inconsistencies are reduced compared to the reconfiguration algorithm according to the ETSI standard for VNF-FGs in multi-domain orchestration.

Payments through cards have become very popular in today's world. All businesses now have options to receive payments through this instrument, moreover most organizations store card information of its customers in some way to enable easy payments in future. Credit card data is a very sensitive information and its theft is a serious threat to any company. Any organization that stores such data needs to achieve payment card industry (PCI) compliance, which is an intricate process. Recently a new paradigm called “tokenization” has been proposed to solve the problem of storage of payment card information. In this paradigm instead of the real credit card data a token is stored. To our knowledge, a formal cryptographic study of this new paradigm has not yet been done. In this paper we formally define the syntax of a tokenization system, and several notions of security for such systems. Finally, we provide some constructions of tokenizers and analyze their security in the light of our definitions.

Privacy of data stored at un-trusted servers is an important problem of today. A solution to this problem can be achieved by encrypting the outsourced data, but simple encryption does not allow efficient query processing. In this paper we propose a novel scheme for encrypting relational databases so that range queries can be efficiently executed on the encrypted data. We formally define the syntax and security of the problem and specify a scheme called ESRQ1. ESRQ1 uses a deterministic encryption scheme along with bitmap indices to encrypt a relational database. We provide details of the functionality of ESRQ1 and prove its security in the specified model.