The entire blockchain is itself stored on every node/computer on the network and grows in a synchronised way: this ensures that the data in any given block cannot be altered without a modification of all blocks created and stored in the network since the transaction considered. Blockchains are usually public and encrypted, using public/private keys, and cryptographic hash functions to perform “proof-of-work”. This means that all participants contribute to the computational power needed to validate new blocks and maintain the system, and that a potential hacker or attacker would have, to be successful, to spend a computational power equivalent to all the computational power mobilised by the network since the recording of the block attacked, and would have to subvert more than half of all computers on the network.