Ethereum co-founder Vitalik Buterin recently provided an in-depth analysis of blockchain's core security mechanisms in a technical article. He pointed out that the unique value of blockchain lies in its "trustless" security guarantee mechanism: even if the system suffers a so-called 51% attack, the attacker cannot disguise an invalid block as a valid one by controlling the majority of hashrate or stake, nor can they directly steal user assets. In other words, blockchain's design gives it "mathematical-grade" tamper resistance at the consensus layer, which is the fundamental distinction between decentralized systems and traditional financial and internet systems.
Vitalik stated that many people misunderstand 51% attacks, believing that if an attacker controls over half of the validators, they can completely overturn the system's rules. However, in reality, such attacks can mostly only cause "short-term chaos" or "transaction reorganizations." They cannot make illegal transactions recognized by the system or directly transfer funds from user wallets. The reason is that the blockchain's consensus mechanism clearly defines "what constitutes a valid state" at the rule level. Therefore, no matter how strong the attacker's hashrate is, as long as the submitted block violates the protocol logic, network nodes will automatically reject it.
But Vitalik also raised an alarming new risk: as more decentralized applications and protocols begin to rely on "off-chain data" or "off-chain judgments," the original security boundaries of blockchain are being redefined. For instance, in oracles, cross-chain bridges, or certain AI-driven governance systems, validators often need to perform tasks not directly constrained by on-chain rules. If 51% of validators collude at this point, they could potentially "lie" in the off-chain component, collectively providing incorrect results. Since such errors fall outside the blockchain's scope of validation, they cannot be automatically corrected by the consensus mechanism, thereby causing user asset security to lose its last line of defense.
He further emphasized that the real risk does not come from the "on-chain" mathematical logic, but from the expansion of "off-chain trust." When we start having blockchain validators take on more off-chain tasks—such as judging real-world events, evaluating external data sources, or arbitrating certain economic behaviors—it introduces a trust dependency similar to that in traditional centralized systems. This means blockchain systems might gradually lose their initial "trustless" characteristic, and this change could be more destructive than purely technical attacks.
Therefore, Vitalik calls on developers and the community to carefully evaluate the scope of "off-chain trust" when designing new protocols and avoid assigning validators tasks that cannot be objectively verified on-chain. He believes the future direction of blockchain development should find a new balance between "security" and "scalability," while simultaneously strengthening the awareness of the boundaries of decentralized consensus. Only in this way can blockchain continue to uphold its core spirit of being trustless, secure, and transparent when facing the complexities of the external world.
