Checkpoints: Protecting Bitcoin from Fraudulent Transactions
A checkpoint refers to the hash value of a block at a specific point in time, registered as a reference point in the
official client that created the Bitcoin system. The official client accepts all transactions up to the checkpoint as valid and irreversible.
In other words, the official client unconditionally recognizes the blockchain—which is a record of transactions occurring before the set checkpoint—as valid
. Conversely, this also means it is impossible to fork the blockchain recorded prior to the checkpoint.
For example, even if a malicious hacker attempts to rewrite the blockchain prior to the checkpoint, the attempt will be rejected, and they cannot alter it arbitrarily. In the world of
Bitcoin, where there is no central organization or administrator and no authority to enforce regulations or monitor activity, checkpoints serve as a tool to prevent fraudulent transactions from infiltrating the network and ensure that legitimate transactions continue.
Regarding Bitcoin’s mining speed, a major concern is that controlling a majority of the network could enable fraudulent transactions; checkpoints are sometimes used as a countermeasure against this 51% attack.
