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Many blockchain applications require democratic on-chain decision-making. In this work, we propose a community-inclusive decentralised collaborative decision-making system with privacy assurance. Its key component is a two-stage voting scheme inspired by choice architecture. Our decision-making system is compatible with most existing blockchain infrastructures. In addition, it supports liquid democracy/delegative voting for better collaborative intelligence. Namely, stake holders can either vote directly on proposals or delegate their voting power to experts. When majority of voting committee members are honest, no one can derive voters' voting preferences or delegations with non-negligible probability. To support concurrent multiple voting events, we design a distributed batch key generation protocol that can generate multiple keys simultaneously by voting committee members with amortised communication cost of O(n) per key, where n is the number of participants. Besides, our system supports "evolving committee", i.e., voting committee members can be changed during the voting period. We implemented a pilot system in Scala, benchmark results indicate that our system can support large number of participants with high efficiency.

A specific number of transaction confirmation blocks determines average time of receiving and accepting payments at cryptocurrencies, and the shortest confirmation time for the same level of blockchain security provides the best user properties. Existing papers on transaction confirmation blocks for Bitcoin use implicit assumption of prompt spreading of Bitcoin blocks over the network (that is not always the case for the real world conditions). The newer publications with rigorous analysis and proofs of Bitcoin blockchain properties that take into account network delays provide asymptotic estimates, with no specific numbers for transaction confirmation blocks. We propose three methods for determination of required number of confirmation blocks for Bitcoin and GHOST on networks with delayed message delivery with different models that take into account the possibility of faster adversarial node syncronization. For the GHOST we propose the first (to our knowledge) strict theoretical method that allows to get required number of confirmation blocks for a given attacker's hashrate and attack success probability.

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