Definition ∞ A long range attack is a sophisticated form of attack against Proof-of-Stake blockchains where an attacker attempts to rewrite a significant portion of the chain’s history from an early point. This is achieved by compromising old private keys of validators who are no longer active on the chain. The attacker then uses these keys to forge an alternative, longer chain that originates from a point far back in time. Such an attack exploits the fact that old stakes are no longer economically active, making it potentially cheaper to acquire historical validator keys.
Context ∞ Long range attacks are a theoretical but serious security concern for Proof-of-Stake blockchains, frequently highlighted in academic research and protocol design discussions. News articles might mention these attacks when discussing the security models of various PoS protocols and the mechanisms designed to mitigate them, such as checkpointing or withdrawal delays. The ongoing challenge for PoS systems is to devise methods that prevent such historical rewrites without sacrificing decentralization or introducing excessive complexity.
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