A message digest is the result of a one-way hashing operation that produces a unique value for a given unique string of data. Its primary use is to detect any unauthorized changes in data (verify its data integrity).

For example, suppose you have a database record with 10 sensitive data fields, and you need to determine if any of the fields have been unexpectedly changed. Before you create or update the database record you can hash the 10 sensitive fields into a single message digest and store the digest under the same record key. Each time you read the database record, you can check its data integrity by hashing the same 10 fields and compare the resulting message digest with the one currently stored for that record. If the two message digests do not match exactly, the data has undergone an unauthorized modification.