In Ethereum, private transactions, a specialized transaction type employed to evade public Peer-to-Peer (P2P) network broadcasting, remain largely unexplored, particularly in the context of the transition from Proof-of-Work (PoW) to Proof-of-Stake (PoS) consensus mechanisms. To address this gap, we investigate the transaction characteristics, (un)intended usages, and monetary impacts by analyzing large-scale datasets comprising 14,810,392 private transactions within a 15.5-month PoW dataset and 30,062,232 private transactions within a 15.5-month PoS dataset. While originally designed for security purposes, we find that private transactions predominantly serve three distinct functions in both PoW and PoS Ethereum: extracting Maximum Extractable Value (MEV), facilitating monetary transfers to distribute mining rewards, and interacting with popular Decentralized Finance (DeFi) applications. Furthermore, we find that private transactions are utilized in DeFi attacks to circumvent surveillance by white hat monitors, with an increased prevalence observed in PoS Ethereum compared to PoW Ethereum. Additionally, in PoS Ethereum, there is a subtle uptick in the role of private transactions for MEV extraction. This shift could be attributed to the decrease in transaction costs. However, this reduction in transaction cost and the cancellation of block rewards result in a significant decrease in mining profits for block creators.

翻译：在以太坊中，私有交易作为一种用于规避公共点对点（P2P）网络广播的特殊交易类型，其研究仍相当匮乏，尤其是在从工作量证明（PoW）向权益证明（PoS）共识机制过渡的背景下。为填补这一空白，我们通过分析大规模数据集，研究了私有交易的特性、（非）预期用途及货币影响。数据集包含PoW阶段15.5个月内的14,810,392笔私有交易，以及PoS阶段15.5个月内的30,062,232笔私有交易。研究发现，尽管私有交易最初是为安全目的而设计，但在PoW和PoS以太坊中，它们主要服务于三个不同功能：提取最大可提取价值（MEV）、促进矿工奖励分发的货币转移，以及与主流去中心化金融（DeFi）应用交互。此外，我们发现私有交易被用于DeFi攻击，以规避白帽监控器的监视，且与PoW以太坊相比，其在PoS以太坊中的使用更为普遍。另外，在PoS以太坊中，私有交易在MEV提取方面的作用略有上升。这一转变可能归因于交易成本的降低。然而，交易成本的降低和区块奖励的取消，导致区块创建者的挖矿利润显著下降。