This file was created by the TYPO3 extension bib --- Timezone: CEST Creation date: 2024-04-25 Creation time: 02-36-40 --- Number of references 4 inproceedings 2022_matzutt_redactchain 2022 5 3 Blockchains gained tremendous attention for their capability to provide immutable and decentralized event ledgers that can facilitate interactions between mutually distrusting parties. However, precisely this immutability and the openness of permissionless blockchains raised concerns about the consequences of illicit content being irreversibly stored on them. Related work coined the notion of redactable blockchains, which allow for removing illicit content from their history without affecting the blockchain's integrity. While honest users can safely prune identified content, current approaches either create trust issues by empowering fixed third parties to rewrite history, cannot react quickly to reported content due to using lengthy public votings, or create large per-redaction overheads. In this paper, we instead propose to outsource redactions to small and periodically exchanged juries, whose members can only jointly redact transactions using chameleon hash functions and threshold cryptography. Multiple juries are active at the same time to swiftly redact reported content. They oversee their activities via a global redaction log, which provides transparency and allows for appealing and reversing a rogue jury's decisions. Hence, our approach establishes a framework for the swift and transparent moderation of blockchain content. Our evaluation shows that our moderation scheme can be realized with feasible per-block and per-redaction overheads, i.e., the redaction capabilities do not impede the blockchain's normal operation. redactable blockchain; illicit content; chameleon hash functions; threshold cryptography mynedata; impact-digital; digital-campus https://www.comsys.rwth-aachen.de/fileadmin/papers/2022/2022-matzutt-redactchain.pdf IEEE Proceedings of the 2022 IEEE International Conference on Blockchain and Cryptocurrency (ICBC '22), May 2-5, 2022, Shanghai, China Shanghai, China May 2-5, 2022 978-1-6654-9538-7/22 10.1109/ICBC54727.2022.9805508 1 RomanMatzutt VincentAhlrichs JanPennekamp RomanKarwacik KlausWehrle article 2021_matzutt_coinprune_v2 IEEE Transactions on Network and Service Management 2021 9 10 18 3 3064-3078 Popular cryptocurrencies continue to face serious scalability issues due to their ever-growing blockchains. Thus, modern blockchain designs began to prune old blocks and rely on recent snapshots for their bootstrapping processes instead. Unfortunately, established systems are often considered incapable of adopting these improvements. In this work, we present CoinPrune, our block-pruning scheme with full Bitcoin compatibility, to revise this popular belief. CoinPrune bootstraps joining nodes via snapshots that are periodically created from Bitcoin's set of unspent transaction outputs (UTXO set). Our scheme establishes trust in these snapshots by relying on CoinPrune-supporting miners to mutually reaffirm a snapshot's correctness on the blockchain. This way, snapshots remain trustworthy even if adversaries attempt to tamper with them. Our scheme maintains its retrospective deployability by relying on positive feedback only, i.e., blocks containing invalid reaffirmations are not rejected, but invalid reaffirmations are outpaced by the benign ones created by an honest majority among CoinPrune-supporting miners. Already today, CoinPrune reduces the storage requirements for Bitcoin nodes by two orders of magnitude, as joining nodes need to fetch and process only 6 GiB instead of 271 GiB of data in our evaluation, reducing the synchronization time of powerful devices from currently 7 h to 51 min, with even larger potential drops for less powerful devices. CoinPrune is further aware of higher-level application data, i.e., it conserves otherwise pruned application data and allows nodes to obfuscate objectionable and potentially illegal blockchain content from their UTXO set and the snapshots they distribute. blockchain; block pruning; synchronization; bootstrapping; scalability; velvet fork; Bitcoin mynedata; impact_digital; digital_campus https://www.comsys.rwth-aachen.de/fileadmin/papers/2021/2021-matzutt-coinprune-v2.pdf English 1932-4537 10.1109/TNSM.2021.3073270 1 RomanMatzutt BenediktKalde JanPennekamp ArthurDrichel MartinHenze KlausWehrle inproceedings 2020_matzutt_anonboot 2020 10 7 531-542 Distributed anonymity services, such as onion routing networks or cryptocurrency tumblers, promise privacy protection without trusted third parties. While the security of these services is often well-researched, security implications of their required bootstrapping processes are usually neglected: Users either jointly conduct the anonymization themselves, or they need to rely on a set of non-colluding privacy peers. However, the typically small number of privacy peers enable single adversaries to mimic distributed services. We thus present AnonBoot, a Sybil-resistant medium to securely bootstrap distributed anonymity services via public blockchains. AnonBoot enforces that peers periodically create a small proof of work to refresh their eligibility for providing secure anonymity services. A pseudo-random, locally replicable bootstrapping process using on-chain entropy then prevents biasing the election of eligible peers. Our evaluation using Bitcoin as AnonBoot's underlying blockchain shows its feasibility to maintain a trustworthy repository of 1000 peers with only a small storage footprint while supporting arbitrarily large user bases on top of most blockchains. anonymization; bootstrapping; public blockchain; Sybil attack; anonymity network; cryptocurrency tumbler; Bitcoin; Tor impact_digital; digital_campus https://www.comsys.rwth-aachen.de/fileadmin/papers/2020/2020-matzutt-anonboot.pdf ACM Proceedings of the 15th ACM ASIA Conference on Computer and Communications Security (ASIACCS '20), October 5-9, 2020, Taipei, Taiwan Taipei, Taiwan ASIACCS 2020 October 5-9, 2020 978-1-4503-6750-9/20/10 10.1145/3320269.3384729 1 RomanMatzutt JanPennekamp ErikBuchholz KlausWehrle inproceedings 2020_matzutt_coinprune 2020 6 24 298-306 Bitcoin was the first successful decentralized cryptocurrency and remains the most popular of its kind to this day. Despite the benefits of its blockchain, Bitcoin still faces serious scalability issues, most importantly its ever-increasing blockchain size. While alternative designs introduced schemes to periodically create snapshots and thereafter prune older blocks, already-deployed systems such as Bitcoin are often considered incapable of adopting corresponding approaches. In this work, we revise this popular belief and present CoinPrune, a snapshot-based pruning scheme that is fully compatible with Bitcoin. CoinPrune can be deployed through an opt-in velvet fork, i.e., without impeding the established Bitcoin network. By requiring miners to publicly announce and jointly reaffirm recent snapshots on the blockchain, CoinPrune establishes trust into the snapshots' correctness even in the presence of powerful adversaries. Our evaluation shows that CoinPrune reduces the storage requirements of Bitcoin already by two orders of magnitude today, with further relative savings as the blockchain grows. In our experiments, nodes only have to fetch and process 5 GiB instead of 230 GiB of data when joining the network, reducing the synchronization time on powerful devices from currently 5 h to 46 min, with even more savings for less powerful devices. blockchain; block pruning; synchronization; bootstrapping; scalability; velvet fork; Bitcoin mynedata; impact_digital; digital_campus https://comsys.rwth-aachen.de/fileadmin/papers/2020/2020-matzutt-coinprune.pdf https://coinprune.comsys.rwth-aachen.de IEEE Proceedings of the 19th IFIP Networking 2020 Conference (NETWORKING '20), June 22-26, 2020, Paris, France Paris, France NETWORKING 2020 June 22-26, 2020 978-3-903176-28-7 1 RomanMatzutt BenediktKalde JanPennekamp ArthurDrichel MartinHenze KlausWehrle