What is Hash Function?

This article on what is hash function is aimed at educating you about this mathematical algorithm or function. As we go further, we will be discussing about hash function and the importance of hash function. In addition, we will be taking a look into how a hash function works. Furthermore, the hash functions in Cryptography will be discussed.

About Hash Function

A mathematical algorithm that converts digital data into an output string with fixated amount of characters is known as hash function. It’s simply the one-way process of converting data which is the message into an output known as the hash. Slight change in a message gives a totally different hash. Therefore, it’s vital to confirm the authenticity of a message with hashing. The authentication of transactions, digital signatures and messages is the role played by this basic tool of modern cryptography.

Due to the fact that hashing tends to be a one-way function, converting a message into a hash is easier than reversing a hash. This is because the reverse of a hash to its original message value is extremely difficult as a huge amount of computing power will be required. As a result of this difficulty though, cryptocurrencies like Bitcoin use it to make sure their blockchain has integrity.

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Importance of Hash Functions

There are vital benefits to using a hash function and they prove why we need hash functions. The advantages of using this mathematical algorithm or function will now be discussed below.

Standard Length

No matter the size of your message, hashing it runs it through a mathematical function and gives an output with a fixed length. This simply means that the hash value produced from the hash function when input is made will remain the same number of characters.

You are Assured of Data Integrity

There are certain times that you just wish to send a digital document or message to someone and you want to ensure it’s not tampered with. Each copy can be verified to see if it’s same by the recipient though this might not work if the message is too much. Having a shorter and fixed number of characters makes it easier for both sender and receiver to check. Confirmation that data has not been tampered with is easier for computers. This is because they compare the two hashes of the data instead of comparing the data in their original form. In that sense, digital data can be checked and the ascertaining of tampering is a major advantage of hash function.

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Verify Authenticity

When an email is sent especially over an unsecured network, it is susceptible to tampering. If tampering occurs on a normal basis, there would be no way that the recipient will know. However, this is not same when the sender signs the email with digital signature and hashes that with the contents of the email. So all the receiver does is examine the hash data to make sure the email was not tampered with. In order to achieve this, the receiver compares the re-generated hash value to the digitally-signed email hash value.

This will be done in conjunction with the public key of the signer. The authenticity of the email is proved by their matching. A recipient knows the message has been tampered with if the hashes are different as a slight change can make the hash totally different.

How Hash Function Works

Firstly, there is a division of the data into fixed-sized blocks known as data blocks in order to get the hash value of a given set. This is due to the fact that data is taken in at a fixed length with hash function. Though, the size of a data block varies from an algorithm to another. Padding will be added to blocks that are not big enough to fill them out. Note however, that no matter the process of hashing you use, the hash value, or output, the length is always fixed. As many times as the amount of data blocks, the hash function is repeated many times.

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Avalanche Effect

The processing of a data block is done one at a time as output of the first data is added along input for the second data block. Therefore, this process makes the combined value of all the blocks the final output. So any slight change in the message, the hash value totally changes and this is the avalanche effect.

Uniqueness and Deterministic

Hash functions must always be deterministic and as such give same output every time you put in the same input. This means that the hash value or output must have uniqueness to the input. There’s no possibility of two different message inputs having the same output hash. When this happens though, it is called a “hash collision” and the algorithm is considered useless.


Hash functions tend to be very irreversible unlike converting a message which is easier. Therefore, computing the hash is quick and easy but the process of reversing it is extremely difficult.

Brute Force Search

Computing the input to get the output hash value requires tons of computing power. Therefore, an act known as brute force search is used to compute and see if a match is produced.

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Hash Functions in Cryptography

Hash functions are quite popular in cryptography as the most renowned cryptocurrency, Bitcoin uses it in their blockchain. In order to solve hashes, lots of standard computers known as miners race each other in a brute force search. A proof-of-work known as NONCE is computed in the solving of a hash. The block’s hash will be made to start from a particular number of zeroes. Therefore, a block can be considered valid and added to the blockchain immediately a proof-of-work is discovered.

Since a cryptographic algorithm is used to create each block’s hash, Bitcoin uses the SHA-256 algorithm. So what Bitcoin miners mostly do is run numbers through a cryptographic algorithm till they can guess the valid NONCE.

Hashing vs Encryption

The act of creating a scrambled message from data so that only someone with a corresponding key can decode it is known as encryption. This two-way function is structured to be reversible by anyone holding the cipher. So the intention of decrypting later on comes with encrypting something. Meanwhile hashing on the other hand, uses a formula to convert data of any size to a fixed length. Generally, hashing is a one-way function unlike encryption which is two-way function as the reverse is extremely difficult. While encryption protects data in transit, hashing confirms if a data has been tampered with or not.

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Hopefully, we have educated you on what is hash function with this article. Verifying authenticity is made a lot faster and easier with hash function. Therefore, it serves like a tamper seal to indicate when data has been altered.

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