Regionalism and redistribution in South Korea

In South Korea, it has been widely known that an incumbent president allocates a disproportionally larger amount of intergovernmental transfers to regions with more loyal supporters. It has been also believed that despite a government change in 1997, this positive and linear relationship between support for an incumbent president and allocated public funds did not change. We show that neither is valid. Based on a formal model, we argue that an incumbent president allocates a larger amount not only in his own turf but also in his rival's and a smaller amount in regions where votes are divided more evenly between candidates. This quadratic relationship between vote and money is highly significant under the Kim Young Sam administration (1993--1997) but not significant during the Kim Dae Jung administration (1998--2002)

Short Selling Attack: A Self-Destructive But Profitable 51% Attack On PoS Blockchains

There have been several 51% attacks on Proof-of-Work (PoW) blockchains recently, including Verge and GameCredits, but the most noteworthy has been the attack that saw hackers make off with up to $18 million after a successful double spend was executed on the Bitcoin Gold network. For this reason, the Proof-of-Stake (PoS) algorithm, which already has advantages of energy efficiency and throughput, is attracting attention as an alternative to the PoW algorithm. With a PoS, the attacker needs to obtain 51% of the cryptocurrency to carry out a 51% attack. But unlike PoW, attacker in a PoS system is highly discouraged from launching 51% attack because he would have to risk losing his entire stake amount to do so. Moreover, even if a 51% attack succeeds, the value of PoS-based cryptocurrency will fall, and the attacker with the most stake will eventually lose the most. In this paper, we try to derive the results that go against these conventional myths. Despite of the significant depreciation of cryptocurrency, our method can make a profit from a 51% attack on the PoS blockchains using the traditional stock market\u27s short selling (or shorting) concept. Our findings are an example to show that the conventional myth that a destructive attack that destroys the blockchain ecosystem totally will not occur because it is fundamentally unprofitable to the attacker itself may be wrong

Countering Block Withholding Attack Effciently

Bitcoin, well-known cryptocurrency, selected Poof-of-Work (PoW) for its security. PoW mechanism incentivizes participants and deters attacks on the network. Bitcoin seems to have operated the stable distributed network with PoW until now. Researchers found, however, some vulnerabilities in PoW such as selfish mining, block withholding attack, and so on. Especially, after Rosenfeld suggested block withholding attack and Eyal made this attack practical, many variants and countermeasures have been proposed. Most countermeasures, however, were accompanied by changes in the mining algorithm to make the attack impossible, which lowered the practical adaptability. In this paper, we propose a countermeasure to prevent block withholding attack effectively. Mining pools can adapt our method without changing their mining environment

Pooled Mining Makes Selfish Mining Tricky

Bitcoin, the first successful cryptocurrency, uses the blockchain structure and PoW mechanism to generate blocks. PoW makes an adversary difficult to control the network until she retains over 50\% of the hashrate of the total network. Another cryptocurrency, Ethereum, also uses this mechanism and it did not make problem before. In PoW research, however, several attack strategies are studied. In this paper, we researched selfish mining in the pooled mining environment and found the pooled mining exposes mining information of the block which adversary is mining to the random miners. Using this leaked information, other miners can exploit the selfish miner. At the same time, the adversary loses revenue than when she does honest mining. Because of the existence of our counter method, the adversary with pooled mining cannot do selfish mining easily on Bitcoin or blockchains using PoW

Detective Mining: Selfish Mining Becomes Unrealistic under Mining Pool Environment

One of Bitcoin’s core security guarantees is that, for an attacker to be able to successfully interfere with the Bitcoin network and reverse transactions, they need to control 51% of total hash power. Eyal et al., however, significantly reduces Bitcoin’s security guarantee by introducing another type of attack, called Selfish Mining . The key idea behind selfish mining is for a miner to keep its discovered blocks private, thereby intentionally forking the chain. As a result of a selfish mining attack, even a miner with 25% of the computation power can bias the agreed chain with its blocks. After Eyal\u27s original paper, the concept of selfish mining has been actively studied within the Bitcoin community for several years. This paper studies a fundamental problem regarding the selfish mining strategy under the existence of mining pools. For this, we propose a new attack strategy, called Detective Mining , and show that selfish mining pool is not profitable anymore when other miners use our strategy

FedTherapist: Mental Health Monitoring with User-Generated Linguistic Expressions on Smartphones via Federated Learning

Psychiatrists diagnose mental disorders via the linguistic use of patients. Still, due to data privacy, existing passive mental health monitoring systems use alternative features such as activity, app usage, and location via mobile devices. We propose FedTherapist, a mobile mental health monitoring system that utilizes continuous speech and keyboard input in a privacy-preserving way via federated learning. We explore multiple model designs by comparing their performance and overhead for FedTherapist to overcome the complex nature of on-device language model training on smartphones. We further propose a Context-Aware Language Learning (CALL) methodology to effectively utilize smartphones' large and noisy text for mental health signal sensing. Our IRB-approved evaluation of the prediction of self-reported depression, stress, anxiety, and mood from 46 participants shows higher accuracy of FedTherapist compared with the performance with non-language features, achieving 0.15 AUROC improvement and 8.21% MAE reduction.Comment: Accepted to the 2023 Conference on Empirical Methods in Natural Language Processing (EMNLP 2023

Opportunism and Opportunity Cost as Antecedents of Participatory Behavior

Despite its positive impacts, public participation often begets a representativeness problem due to participants’ opportunism and opportunity cost. Using the survey on 2,000 citizens in South Korea, the research results show that: (1) citizens’ opportunism in terms of self-interest or free-riding may significantly influence their participatory behaviors and (2) citizens’ opportunity costs may act as a mediating factor, i.e., a higher opportunity cost lessens the impact of opportunism on participation. The findings imply that a desirably represented citizen participation can be supported by considering and mobilizing (not manipulating) citizens’ sense of opportunism and opportunity cost