Definition ∞ An adversary majority refers to a situation where a hostile group controls a sufficient portion of a decentralized network to disrupt its normal operation. This control typically involves a majority of computational power or staked assets in a blockchain consensus mechanism. Such a concentration of power allows the malicious entity to potentially manipulate transaction order, prevent valid transactions from confirming, or execute double-spend attacks. The existence of an adversary majority fundamentally challenges the security guarantees of a distributed ledger system.
Context ∞ Understanding an adversary majority is crucial for evaluating the security robustness of various blockchain protocols, particularly in proof-of-work or proof-of-stake systems. News often reports on potential vulnerabilities or actual attacks where a significant portion of network control is obtained, highlighting the continuous efforts to maintain decentralization and prevent such concentrations of power. Debates around network centralization frequently relate to the theoretical or practical possibility of an adversary majority forming.
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