Browsing by Author "Kiraz, Mehmet Sabir"

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    NFT Trades in Bitcoin with Off-Chain Receipts
    (Springer, 2023-10-04) Kiraz, Mehmet Sabir; Larraia, Enrique; Vaughan, Owen
    Non-fungible tokens (NFTs) are digital representations of assets stored on a blockchain. It allows content creators to certify authenticity of their digital assets and transfer ownership in a transparent and decentralized way. Popular choices of NFT marketplaces infrastructure include blockchains with smart contract functionality or layer-2 solutions. Surprisingly, researchers have largely avoided building NFT schemes over Bitcoin-like blockchains, most likely due to high transaction fees in the BTC network and the belief that Bitcoin lacks enough programmability to implement fair exchanges. In this work we fill this gap. We propose an NFT scheme where trades are settled in a single Bitcoin transaction as opposed to executing complex smart contracts. We use zero-knowledge proofs (concretely, recursive SNARKs) to prove that two Bitcoin transactions, the issuance transaction tx0 and the current trade transaction txn, are linked through a unique chain of transactions. Indeed, these proofs function as “off-chain receipts” of ownership that can be transferred from the current owner to the new owner using an insecure channel. The size of the proof receipt is short, independent of the total current number of trades n, and can be updated incrementally by anyone at anytime. Marketplaces typically require some degree of token ownership delegation, e.g., escrow accounts, to execute the trade between sellers and buyers that are not online concurrently, and to alleviate transaction fees they resort to off-chain trades. This raises concerns on the transparency and purportedly honest behaviour of marketplaces. We achieve fair and non-custodial trades by leveraging our off-chain receipts and letting the involved parties carefully sign the trade transaction with appropriate combinations of sighash flags.
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    Security, Privacy, and Decentralized Trust Management in VANETs: A Review of Current Research and Future Directions
    (ACM, 2024) AlMarshoud, Mishri Saleh; Al-Bayatti, Ali H.; Kiraz, Mehmet Sabir
    Vehicular Ad Hoc Networks (VANETs) are powerful platforms for vehicular data services and applications. The increasing number of vehicles has made the vehicular network diverse, dynamic, and large-scale, making it difficult to meet the 5G network’s demanding requirements. Decentralized systems are interesting and provide attractive services because they are publicly available (transparency), have an append-only ledger (robust integrity protection), remove single points of failure, and enable distributed key management and communication in a peer-to-peer network. Researchers dedicated substantial efforts to advancing vehicle communications, however conventional cryptographic mechanisms are insufficient which enabled us to look at decentralized technologies. Therefore, we revisit decentralized approaches with VANETs. Endpoint devices hold a wallet which may incorporate threshold key management methods like MPC wallets, HD Wallets, or multi-party threshold ECDSA/EdDSA/BLS. We also discuss trust management approaches and demonstrate how decentralization can improve integrity, security, privacy, and resilience to single points of failure. We also conduct a comprehensive review, comparing them with current requirements, and the latest authentication and secure communication architectures, which require the involvement of trusted but non-transparent authorities in certificate issuance/revocation. We highlight the limitations of these schemes from PKI deployment and recommend future research, particularly in the realm of quantum cryptography.