Hashing and data integrity

Hashing is where the data inside a document is hashed using an algorithm such as a Secure Hash Algorithm version 1 (SHA1) and MD5. This turns the data inside the file into a long text string known as a hash value; this is also known as a message digest.

While you are hashing the same data, if you copy a file and therefore have two files containing the same data, if you hash them with the same hashing algorithm, it will always produce the same hash value. Please look at the following example:

• Verifying Integrity: During forensic analysis, the scientist takes a copy of the data prior to investigation. To ensure that he has not tampered with it during investigation, he will hash the data before starting and then compare the hash to the data when he has finished. If the hash matches, then we know that the integrity of the data is intact.
• One-way Function: For the purpose of the exam, hashing is a one-way function and cannot be reversed.
• HMAC Authentication: In cryptography...