What is a message digest?

A message digest is a smaller version of the original message, created through a process called hashing. This process transforms the input data (the original message) into a fixed-size string of characters, which appears random. The primary purpose of a message digest is integrity verification; it allows one to check whether the original data has been altered. When data is hashed, even a small change in the original input will result in a significantly different hash value, making it easy to detect modifications.

Additionally, message digests are used in various security applications, such as digital signatures and password storage, where it is important to ensure that the data has not changed or been compromised. Because message digests are typically much smaller (in terms of data size) than the original data, they facilitate efficient storage and comparison.