What characteristic of Blockchain ensures that past records cannot be modified?

The characteristic of blockchain that ensures past records cannot be modified is immutability. This feature is fundamental to how blockchain technology operates. When data is added to a blockchain, it's cryptographically linked to the previous block, creating a chain. Each block contains a unique hash of the previous block, along with a timestamp and the transaction data. Once this information is added and confirmed by the network, altering any record would change the hash and thus break the chain.

Immutability enhances security, trust, and transparency in transactions because once data is recorded on the blockchain, it becomes extremely difficult to change or delete it without network consensus. This characteristic makes blockchain particularly valuable for applications that require reliable record-keeping, such as financial transactions, supply chain management, and more.

In contrast, flexibility refers to the ability of a system to adapt to changes, scalability pertains to the capacity of a system to handle growth, and interoperability reflects the ability of different systems to work together. While these aspects are important in various contexts, they do not address the essential capability of ensuring that past records remain unchanged.