本文建構一個涵蓋合法與非法交易的兩部門貨幣搜尋模型，並納入加密貨幣與現金交易管道，探討加密貨幣對於非法交易的影響。非法交易之下，現金與加密貨幣的差異在於，現金交易會因資訊不對稱的問題產生交易障礙；加密貨幣交易則是透過暗網平台所提供的第三方支付交易模式來降低資訊不對稱的問題，提高交易成功率。然而，透過暗網平台交易時，需額外付出平台使用費，因而增加交易成本。本文設定兩種非法交易管道，在不同交易特性與查緝機率下對於均衡狀態的影響。模擬結果發現只有當兩種交易管道的查緝機率皆足夠低時，兩種貨幣才有機會同時在經濟體中流通。再者，查緝機率的提升會使得貨幣實質價值下降，讓合法與非法搜尋市場交易量下降，以及非法搜尋市場交易比例下降。而一旦查緝機率超過臨界值時，可能會使經濟體從加密貨幣與現金皆流通的混合均衡跳至單一貨幣流通均衡，減少非法市場買賣雙方在交易配對上的摩擦，這反而會使得非法市場交易量與非法交易比例的上升。

This paper constructs a two sector monetary search model covering legal and illegal markets, and incorporates cryptocurrency and cash trading channels to explore the impact of cryptocurrency on illegal transactions. We compare the differences between cryptocurrency and cash in illegal transactions：cryptocurrency improves the security of transactions through a transaction mode of third-party payment on the darknet markets platform, but the platform usage fee is required; cash will cause transaction barriers due to information asymmetry, but no additional transaction costs will be paid.
In this paper, we investigate the influences of different trading environment and seizure probability on equilibrium states. The results show that the cash and cryptocurrency exist at the same time if the probability of seizure is low enough. Moreover, the increase in the probability of government seizure in most of cases leads to a decline in the number of legal and illegal transactions, as well as a decline in the proportion of illegal transactions. However, in the cases that government raises the seizure probability over the thresholds may make the economy jump from the mixed equilibrium of both currencies to the single equilibrium, which will increase the number of transactions and the proportion of illegal transactions.

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