What’s a common use case for using a hash function in security?

Using a hash function to ensure data integrity is a fundamental application in security practices. A hash function takes input data and produces a fixed-size string of characters, which is typically a digest that uniquely represents the original data. If even a single bit of the input data changes, the output hash will change significantly, which is a property called the "avalanche effect."

This characteristic makes hash functions useful for verifying the integrity of data. For instance, when data is transmitted across a network or stored, the hash of that data can be calculated before transmission or storage. Later, the recipient or user can re-calculate the hash of the received or retrieved data and compare it to the original hash. If the two hashes match, it confirms that the data has not been altered or corrupted, thereby ensuring its integrity.

While other choices may relate to security functions—such as user authentication or data encryption—hash functions specifically excel at confirming that an unaltered copy of the data exists. User authentication often involves other mechanisms, such as passwords or tokens, and data encryption focuses on securing data confidentiality rather than its integrity. Data compression, although it can involve hashing techniques in some contexts, does not typically utilize hash functions for security purposes.