Once purely theoretical, “majority” or “51%” attacks on public blockchains have dealt participants a reality check: The fundamental assumption of Satoshi Nakamoto’s 2008 Bitcoin whitepaper (that computing power will remain sufficiently decentralized in blockchain networks that rely on a “proof-of-work” consensus mechanism) can in practice actually be exploited to enable double spending.

“The system is secure as long as honest nodes collectively control more CPU power than any cooperating group of attacker nodes…. If a majority of CPU power is controlled by honest nodes, the honest chain will grow the fastest and outpace any competing chains. To modify a past block, an attacker would have to redo the proof-of-work of the block and all blocks after it and then catch up with and surpass the work of the honest nodes.” – Satoshi Nakamoto, Bitcoin: A Peer-to-Peer Electronic Cash System

These incidents have provided opportunities for developers of both public and private blockchains, as well as operators of blockchain-based digital asset trading platforms, to learn from the first generation of blockchain deployments.