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Vaccination passports are being issued by governments around the world in order to open up their travel and hospitality sectors. Civil liberty campaigners on the other hand argue that such mandatory instruments encroach upon our fundamental right to anonymity, freedom of movement, and are a backdoor to issuing "identity documents" to citizens by their governments. In this paper we present a privacy-preserving framework that uses two-factor authentication to create a unique identifier that can be used to locate a person's vaccination record on a blockchain, but does not store any personal information about them. Our main contribution is the employment of a locality sensitive hashing algorithm over an iris extraction technique, that can be used to authenticate users and anonymously locate vaccination records on the blockchain, without leaking any personally identifiable information to the blockchain. Our proposed system allows for the safe reopening of society, while maintaining the privacy of citizens.

The Internet of Things (IoT) is the collection of everyday smart devices which connect to the Cloud, often through Fog nodes, to transmit and receive information. These everyday devices are distinct from traditional computers because they typically have notable constraints on their RAM, flash memory, and computational power. Due to these constraints, we believe that many of the proposed encryption schemes are too heavyweight to be employed in the IoT. In this paper we present a lightweight, flexible encryption scheme that relies on the one-way information loss property of a secure hash function. Our scheme imposes minimal computational and storage requirements, and imposes no non-negligible burdens on the encrypting device, except for the hash itself. We find that the encryption algorithm is particularly lightweight, and holds up strongly in terms of its speed and memory efficiency.

Numerous electronic cash schemes have been proposed over the years - however none have been embraced by financial institutions as an alternative to fiat currency. David Chaum's ecash scheme was the closest to something that mimicked a modern day currency system, with the important property that it provided anonymity for users when purchasing coins from a bank, and subsequently spending them at a merchant premises. However it lacked a crucial element present in current fiat-based systems - the ability to continuously spend or transfer coins. Bitcoin reignited the interest in cryptocurrencies in the last decade but is now seen as more of an asset store as opposed to a financial instrument. One interesting thing that has come out of the Bitcoin system is blockchains and the associated distributed consensus protocols. In this paper we propose a transferable electronic cash scheme using blockchain technology which allows users to continuously reuse coins within the system.

Cryptocurrencies have received a lot of research attention in recent years following the release of the first cryptocurrency Bitcoin. With the rise in cryptocurrency transactions, the need for smart contracts has also increased. Smart contracts, in a nutshell, are digitally executed contracts wherein some parties execute a common goal. The main problem with most of the current smart contracts is that there is no privacy for a party's input to the contract from either the blockchain or the other parties. Our research builds on the Hawk project that provides transaction privacy along with support for smart contracts. However, Hawk relies on a special trusted party known as a manager, which must be trusted not to leak each party's input to the smart contract. In this paper, we present a practical private smart contract protocol that replaces the manager with an MPC protocol such that the function to be executed by the MPC protocol is relatively lightweight, involving little overhead added to the smart contract function, and uses practical sigma protocols and homomorphic commitments to prove to the blockchain that the sum of the incoming balances to the smart contract matches the sum of the outgoing balances., Comment: 9 pages, 6 figures, published in IEEE BRAINS'21 Conference Proceedings

The amalgamation of different generations of mobile cellular networks around the globe has resulted in diverse data speed experiences for end users. At present there are no defined mechanisms in place for a subscriber of one mobile network operator (MNO) to use the services of a WiFi provider. Cellular and Data Service providers also have no standardized procedures to securely interact with each other, and to allow their subscribers to use third party services on a pay-as-you-go basis. This paper proposes a blockchain-based offloading framework that allows a subscriber of a mobile operator to temporarily use another MNO or WiFi provider's higher speed network. Smart contracts allow diverse entities such as MNOs, Brokers and WiFi Providers to automatically execute mutual agreements to enable the utilization of third party infrastructure in a secure and controlled manner. To test the proposed framework, the offloading of a subscriber from 3G/4G/4G-LTE/5G networks to a fixed broadband WiFi network was carried out and the results analyzed. The offloading framework was implemented using the ns-3 network simulator, and the Ethereum blockchain smart contract features were used for the settlement of invoices.

In the era of social media and messaging applications, people are becoming increasingly aware of data privacy issues associated with such apps. Major messaging applications are moving towards end-to-end encryption (E2EE) to give their users the privacy they are demanding. However the current security mechanisms employed by different service providers are not unfeigned E2EE implementations, and are blended with many vulnerabilities. In the present scenario, the major part of the E2EE mechanism is controlled by the service provider's servers, and the decryption keys are stored by them in case of backup restoration. These shortcomings diminish the user's confidence in the privacy of their data while using these apps. A public Key infrastructure (PKI) mechanism can be used to circumvent some of these issues, but it comes with high monetary costs, which makes it impossible to roll out for millions of users. The paper proposes a blockchain-based E2EE framework that can mitigate the contemporary vulnerabilities in messaging applications. The user's device generates the public/private key pair during application installation, and asks its mobile network operator (MNO) to issue a digital certificate and store it on the blockchain. A user can fetch a certificate for another user from the chat server and communicate securely with them using a ratchet forward encryption mechanism.

Over the past decade, we have witnessed the Internet becoming increasingly centralized in the hands of a small number of giant technology firms, that control many of the most popular applications and the content they host on their platforms. In addition, in the majority of instances today, access to the Internet is usually provided through local internet service providers (ISPs) in each country. Governments in different jurisdictions can exert pressure on these technology firms and ISPs to enforce restrictions on Internet usage by their citizens, such as the blocking access to certain sites and/or content. In this paper, we present a promising new approach to circumventing some of these issues. Our decentralized web (DWeb) proposal makes use of a mesh network to connect community based routers. In addition, objects on the DWeb are indexed using Bblockchain technology, which allows for secure storage of immutable object references, and integrity checking of the data being served to users. Our DWeb design is also capable of operating during network partitions, and is able to quickly re-synchronize with the larger network once connectivity has been restored., Comment: 7 pages

Uniquely identifying individuals across the various networks they interact with on a daily basis remains a challenge for the digital world that we live in, and therefore the development of secure and efficient privacy preserving identity mechanisms has become an important field of research. In addition, the popularity of decentralised decision making networks such as Bitcoin has seen a huge interest in making use of distributed ledger technology to store and securely disseminate end user identity credentials. In this paper we describe a mechanism that allows one to store the COVID-19 vaccination details of individuals on a publicly readable, decentralised, immutable blockchain, and makes use of a two-factor authentication system that employs biometric cryptographic hashing techniques to generate a unique identifier for each user. Our main contribution is the employment of a provably secure input-hiding, locality-sensitive hashing algorithm over an iris extraction technique, that can be used to authenticate users and anonymously locate vaccination records on the blockchain, without leaking any personally identifiable information to the blockchain.

Zero-knowledge proofs have always provided a clear solution when it comes to conveying information from a prover to a verifier or vice versa without revealing essential information about the process. Advancements in zero-knowledge have helped develop proofs which are succinct and provide non-interactive arguments of knowledge along with maintaining the zero-knowledge criteria. zk-SNARKs (Zero knowledge Succinct Non-Interactive Argument of Knowledge) are one such method that outshines itself when it comes to advancement of zero-knowledge proofs. The underlying principle of the Zcash algorithm is such that it delivers a full-fledged ledger-based digital currency with strong privacy guarantees and the root of ensuring privacy lies fully on the construction of a proper zk-SNARK. In this paper we elaborate and construct a concrete zk-SNARK proof from scratch and explain its role in the Zcash algorithm., Comment: 8 pages, 5 figures

A characterization of predicate encryption (PE) with support for homomorphic operations is presented and we describe the homomorphic properties of some existing PE constructions. Even for the special case of IBE, there are few known group-homomorphic cryptosystems. Our main construction is an XOR-homomorphic IBE scheme based on the quadratic residuosity problem (variant of the Cocks' scheme), which we show to be strongly homomorphic. We were unable to construct an anonymous variant that preserves this homomorphic property, but we achieved anonymity for a weaker notion of homomorphic encryption, which we call \emph{non-universal}. A related security notion for this weaker primitive is formalized. Finally, some potential applications and open problems are considered., Comment: Full version of a paper that was published in Africacrypt 2013