Generating hashes for each file from the hard drive is the next action that the analyst should perform to ensure the data integrity of the evidence. Hashing is a technique that produces a unique and fixed-length value for a given input, such as a file or a message. Hashing can help to verify the data integrity of the evidence by comparing the hash values of the original and copied files. If the hash values match, then the evidence has not been altered or corrupted. If the hash values differ, then the evidence may have been tampered with or damaged .