• Environmental and Resource Economics Review
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• v.26 no.3
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• pp.399-416
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• 2017

This study examines the problem of efficient scheduling of waste collection in isolated regions like islands when the waste accumulated amount surpasses the standard ceiling by effectively tracking the accumulating trends based on the optimum checking model of Keller (1974). To grasp whether the waste accumulated amount in isolated regions exceeds the standard ceiling, the relevant authorities can tightly check during a set period, but this entails higher monitoring costs. On the other hand, if the accumulated waste over the ceiling is not immediately checked and collected, and continues for a set period of time, innovative efforts for waste management may be highly demanded. As such, the tradeoffs are considered to draw the optimal checking schedule. This study shows that the authorities get to check less frequently the waste accumulation trends if the monitoring costs increase or when the failure rate of waste management systems drops. On the other hand, they get to check more frequently if the accumulated waste amount in isolated regions exceeds the standard ceiling and welfare loss grows as a result. It also shows that frequent checking is the optimal choice if the social marginal benefits enjoyed from innovative efforts made to keep accumulated waste below the standard ceiling, are not significant.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.30 no.3
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• pp.325-336
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• 2020

Nonlinear Invariant Attack is an attack that should be considered when constructing lightweight block ciphers with relatively simple key schedule. A shortcut to prove a block cipher's resistance against nonlinear invariant attack is checking the smallest dimension of linear layer-invariant linear subspace which contains all known differences between round keys is equal to the block size. In this paper, we presents the following results. We identify the structure and number of optimal bit-permutations which require only one known difference between round keys for a designer to show that the corresponding block cipher is resistant against nonlinear invariant attack. Moreover, we show that PRESENT-like block ciphers need at least two known differences between round keys by checking all PRESENT-like bit-permutations. Additionally, we verify that the variants of PRESENT-like bit-permutations requiring the only two known differences between round keys do not conflict with the resistance against differential attack by comparing the best differential trails. Finally, through the distribution of the invariant factors of all bit-permutations that maintain BOGI logic with GIFT S-box, GIFT-variant block ciphers require at least 8 known differences between round keys for the resistance.