Digest and Hash Functions are two important aspects of cryptography. In cryptography, we pass an input text from any algorithm that generates some secured text. Now that algorithm is called a hash function and that secured text is called a digest. From here we can conclude that in cryptography we pass original text from the hash function to generate a digest.

What is Digest?

Digest is the output or the hash value that is generated from the hash table. In cryptography, diget is also known as message digest because it is generated from the message using the hash function. The size of the digest is fixed for any hash function, which means if any hash function produces a digest of size 5 for a message “m1” then it will always produce a digest of size 5 for any type of message.

We can never generate the original message from the digest because there is no such algorithm that can create the same message from the given digest. We always try to have different digest for different messages. Any hashing algorithm is considered good when it has more difference between digest generated from two different messages.

Whenever we pass the same message to the hash function it produces the same digest. And that is why digest is mostly used to check message integrity after transmission by any network. Now let us understand how we can use message digest to verify the integrity

What is the Hash Function?

The Hash Function is one of the important parts of cryptography. It takes input messages and converts them into some fixed-size text. That’s why it is used to provide security to input value.

Hash Function is called so because it hashes the input value. That means it produces a fixed value text or number that is called a hash value and that hash value is usually the index of the hash table where the input text will be stored. So one aspect of Hash Function is to find the location where that input text will be stored. So hash function can do perfect memory management of data by providing the location of storage to every data.

Hashing should not be treated as Encryption because the message that is encrypted can be later decrypted to get the original message. But in hashing once we generate the hash value it can’t be converted back into the original message. So the steps of encryption can be reversed but the steps of hashing can’t be reversed. Yes, but we can get the original message if it is stored at the index equal to the hash value in the hash table, but directly we can’t get the original message from the hash value.

How to Use Message Digest to Verify the Integrity?

When we provide any message to a hash function then it generates a message digest. Now that message digest is used to verify the integrity of the original message

Steps to verify Integrity of Original Message-

• Generate a message digest by passing the original message with a hash function
• Store that Digest with Message in one place and send that collectively
• At the receiver end use the same Hash Function to produce a new message digest from the received message
• If the new message digest is the same as the previous message digest then it is confirmed that the Integrity of the message is preserved
• Otherwise, the Message is changed in between the transmissions and the Integrity of the Message is compromised.

Difference Between Hash Function and Digest

The major difference between Hash Function and Message Digest is as follows-