What are message digests?

Message digests are the output generated by a hash function. A hash function takes an input (or "message") and produces a fixed-size string of characters, which is typically a sequence of numbers and letters. This output, known as a message digest, serves as a unique identifier for the input data. The key characteristic of message digests is that even a small change in the input will produce a significantly different output, making them useful for verifying data integrity.

Message digests are commonly used in various security applications, such as in digital signatures and password hashing, because they can represent a large amount of data in a smaller, more manageable form while still being unique to that original data. They are also designed to be one-way functions, meaning it is computationally infeasible to reverse the process and retrieve the original data from the hash output.

The other options presented do not accurately define message digests: randomly generated numbers for encryption refer to key generation rather than hashing; passwords stored in databases represent sensitive information that may be hashed but are not themselves digests; and data compression methods are used for reducing file size rather than creating unique identifiers for data integrity.