A blockchain is a growing collection of documents known as blocks that are connected together via encryption. Each block includes a cryptographic hash of the preceding block, a timestamp, and transaction data (which is typically written as a Merkle tree). The timestamp demonstrates that the transaction data existed at the moment the block was released in order to be included in its hash. Because each block contains information about the one before it, they create a chain, with each new block strengthening the ones before it. As a result, blockchains are resistant to data tampering since, once recorded, the contents in any one block cannot be changed retrospectively without affecting all subsequent blocks.