Hash Function in Cryptography

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All of the methods and techniques that help to secure data in transit and at rest are used in cryptography. In cryptography, a hash function is a major player, but many people have no idea what it is or what it does.

To be frank, hashing is all over the place. Do you know that your passwords are often hashed and saved on popular websites? Hashing technology is now used in the fingerprint locks on our phones and laptops!

So, let’s look at what a hash function is and why it’s significant in cryptography. We’ll go through how hashing works, what a cryptographic hash function is (and isn’t), and how to improve the security of hashing for password storage.

What Is Hashing? The Definition of a Hash Function in Cryptography

If the shrink wrap on a new phone is ripped or damaged, you can easily tell that the phone has been opened, used, replaced, or damaged. In encryption, a cryptographic hash is similar to a physical hash, except for data instead of a physical entity. Similarly, hashing is similar to applying virtual shrink wrap to a piece of software, application, or data to alert users whether it has been altered in any way.

But, what exactly is hashing? Hashing, also known as a hashing algorithm, is a one-way method that transforms any size input data into fixed-length encoded data. The hash function is located in the middle of the process. Simply put, you can run a short sentence or an entire stream of data through a hash function to produce a string of data of a particular length. It’s a means of concealing the original data in order to make reverse engineering as difficult as possible.

In a more technical sense, it’s a method of shrinking a random amount of input data (called a hash key) into a fixed-length string of bits using a mathematical operation that’s too difficult to reverse with modern computers. So, a hash function is anything that takes input data and uses it to generate a fixed-length output value that is both unique and nearly irreversible (for all practical intents and purposes).

A hash function’s output values are referred to by many different names:

  • Hash values,
  • Digests,
  • Hash codes, or
  • Hashes are all terms for the same thing.

You get a unique hash output for each input. If you’ve created a hash, the only way to duplicate it is to use the same text. Even if you just change one character, the hash value would change. We’ll get into that in a little more depth later.

Hashing vs Encryption — Aren’t They the Same?

In a nutshell? No, it’s not true. The cryptographic processes of hashing and encryption are distinct. Encryption is a method of converting plaintext (readable) data into unreadable data using algorithms and a key. However, you can decrypt the data using either the same (symmetric encryption) or a mathematically similar but different cryptographic key (asymmetric encryption).

A cryptographic hash function, on the other hand, is special. Since hashing is a one-way method, you can’t restore data to its original format once it’s been hashed.

But how do hash functions work and what do they look like? Let’s start with the first part of the question and then move on to the second part later.

Examples of Cryptographic Hash Functions

The performance or hash length is calculated by the hashing algorithm you use. For SHA-1 hashes, the value can be 160 bits; for the SHA-2 family of hashes, the value can be 256 bits, 384 bits, or 512 bits. Hexadecimal characters are widely used to describe them. The quantity and size of the input data can be changed, but the output value is still the same in terms of size.

Consider the following hash inputs and outputs as an example:

Example Input Texts Hash Values Using SHA-1
Hello D364965C90C53DBF14064B9AF4BAABCA72196E2E
Hello! You are reading an article about the cryptographic hash function! B26BACAB73C46D844CABEC26CE32B030FED1164F

The length of the hash value remains the same in this case, whether the input value is a single word or a full sentence. (A 160-bit hash value, for example, has 40 hexadecimal characters, while a 256-bit hash digest has 64.) So, even though I used the same algorithm to hash one of the Harry Potter books — or the whole sequence — the lengths of the hash values will remain the same!

Hash functions can be used in a variety of ways. However, for the purposes of this post, we’ll concentrate on a couple of the ways they’re useful:

  1. Ensuring data integrity,
  2. Creating and verify digital signatures (which are encrypted hashes), and
  3. Facilitating secure password storage.

Providing safe password storage, ensuring data integrity, and creating and verifying digital signatures (encrypted hashes).

The Types of Cryptographic Hash Algorithms

Businesses and companies use a variety of cryptographic hash algorithms (although some are now sunset due to theoretical or practical vulnerabilities). The following are some of the most widely used hashing algorithms:

  • The SHA family (SHA-1, SHA-2 [including SHA-256 and SHA-512], and SHA-3)
  • The MD family (MD)
  • Whirlpool,
  • Tiger,
  • NTLM, and
  • LanMan (LM hash).

Not all of these algorithms are considered safe for any application or function. Some hash functions are fast, while others take a long time to complete. When it comes to cryptographic hash functions, you’ll want to use a slow hash function rather than a fast one when hashing passwords, for example (the slower the better).

Cryptographic Hash Properties

So, what characteristics characterise a stable cryptographic hash function?

  • Determinism — The procedure should always produce the same consistent length output or hash value, regardless of the size of the input or the key value.
  • Computational Speed — The speed of a hash function is critical, and it should vary depending on the application. For example, in some cases, a fast hash function is required, while in others, a slow hash function is preferred.
  • Image Resistance — Reversing hashes should be incredibly difficult (i.e., it should serve as a one-way function for all intents and purposes). Someone should be unable to reverse engineer the hash to determine its original key value due to the complexity of the hash function and the obscurity of the data. Even a minor alteration to the original input can yield a completely different hash value.

Characteristics of a Hash Function in Cryptography

Cryptographic hash functions have two distinguishing characteristics.

A Hash Function Is Practically Irreversible

Hashing is often thought of as a one-way feature. Because of the amount of time and computational resources required, reversing it is highly infeasible (though theoretically possible). That means you can’t deduce the original data from the hash value unless you have an inordinate amount of money.

In other words, the hash value would be h if the hash function is h and the input value is x. (x). It’s (almost) difficult to work out the value of x if you have access to h(x) and know the value of the hash function h.

Hash Values Are Unique

In an ideal world, no two separate input data sets can produce the same hash value. If they do fit, a collision occurs, indicating that the algorithm is unsafe to use and vulnerable to birthday attacks. Collision resistance is a feature that boosts the strength of your hash and makes data more stable. This is due to the fact that a cybercriminal will have to break not only the hash value but also the salt value.

If the hash function is h, and the input data sets are x and y, the hash value of h(x) should always be different from h(y) (y). As a result, h(x) h (y). This means that even the tiniest change in the original data will change the hash value. As a result, no data manipulation goes unnoticed.

How Does Hashing Work?

Let’s take a look at how a hash function operates in cryptography now that we know what it is.

First and foremost, the hashing algorithm divides the large input data into equal-sized blocks. The hashing method is then applied to each data block separately by the algorithm.

While each block is hashed separately, they are all interconnected. The first data block’s hash value is used as an input value and is applied to the second data block. Similarly, the second block’s hashed output is merged with the third block’s hashed output, and the combined input value is hashed once more. The loop continues until you get the final has production, which is the sum of all the blocks involved.

That is, if the data in some block is changed, the hash value of that block changes. Since its hash value is used as an input in subsequent blocks, all of the hash values change. This is how even the tiniest change in the input data can be detected since the hash value changes.

The input value of data block-1 is (B1), and the hash value is h in the diagram (B1). The input value B2 of block 2 is combined with the previous hash value h(B1) to create the hash value h. (B2). This method of comparing the output value of one block with the input value of the next block continues down the line through all of the blocks.

3 Main Features of a Hash Function in Cryptography

Let’s look at what hashing does and doesn’t do in cryptography in the next portion.

It Enables Users to Identify Whether Data Has Been Tampered With

All hash values are different when generated with a unique and random number. As a result, if an attacker attempts to update, alter, or delete some part of the original input data (text data, programme, application, email information, or even the media file), the hash value will change. The users are informed as soon as the hash value changes. Users will instantly notice that the content of a message or a software application has changed since it was received or generated by the original sender/developer.

As a consequence, if a hacker instals malicious code into a software application, the user is warned not to download or instal it because it has been tampered with. Users may also notice whether an attacker modifies the content of an email to trick recipients into sharing sensitive information, transferring money, or downloading a malicious attachment. As a result, they should refrain from taking any of the acts suggested in the letter.

A Hash Function Prevents Your Data from Being Reverse Engineered

When you apply a hash function to data, you get an unintelligible result. So, even if an attacker gains access to the data’s hashed values through a leaking database or a cyber attack, they won’t be able to easily interpret or guess the original (input) data.

Hackers are unlikely to decode the hash value even though they know which hash function (algorithm) was used to hash the data since the hash value cannot be easily reversed using modern tools. It’s simply unfeasible at scale due to the amount of money and time that such a method would necessitate. As a consequence, cryptographic hash is used to secure data when it is in transit or at rest.

You Can’t Retrieve the Data Because It Doesn’t Exist

You can’t recover the original data from the hashed value because hashing is non-reversible. When your goal is to prevent hackers from accessing your plaintext data, this is a good thing. However, if you need to retrieve data for any purpose, a hash function in cryptography may be problematic.

When it comes to password storage, for example, if you have hashed the passwords to store them, you won’t be able to retrieve them if you or your users forget them. The only choice open to you or your users is to reset the password. At the same time, if you simply send a file’s hash value, the receiver will verify its integrity but not convert the hash value to plaintext. To do so, you’ll need to submit the file’s encrypted version as well as its hash value.

Applications of Cryptographic Hash Functions

Any of the preceding information about the cryptographic hash function is purely theoretical. But how useful is it in practise? In cryptography, a hash function is used to map data integrity. Data is protected from leakage by hashing, which compares large chunks of data and detects any data tampering.

Hashing can be used for a number of purposes, including:

  • Digital signatures,
  • Biometrics,
  • Password storage,
  • SSL/TLS certificates,
  • Code signing certificates,
  • Document signing certificates, and
  • Email signing certificates.

You can’t check every code and word of a large piece of data or software when comparing it. When you hash it, however, it transforms large amounts of data into tiny, fixed-length hash values that are much easier to verify and compare.

How Hashing Works in Code Signing

Let’s take a look at how the cryptographic hash function is used for code signing certificates. Assume you’re a software publisher or developer who digitally signatures your downloaded software, scripts, programmes, and executables with code signing certificates. This certificate helps you to inform your customers, clients, and operating systems about your identity (i.e., that you are who you say you are) and the validity of your product. It also employs a hash function that alerts them whether the document has been tampered with after you signed it.

You will use the code signing certificate until you have a final version of your code ready to go. This means that the code signing certificate hashes the entire programme and encrypts it, resulting in the digital signature of the publisher or creator.

When a user instals your software, their operating system produces a hash value to compare to your software’s initial hash value. If it does, that’s fantastic; it means they can continue with confidence knowing what they do. However, if anyone attempts to deceive you by changing your programme or digital signature, the hash value they create will no longer match your original hash, and the user will be informed.

This ensures that a hash value that hasn’t been tampered with guarantees the quality of your apps. In this case, the cryptographic hash function means that no one can change your programme without your knowledge.

How Hashing Works in Password Storage

This section is particularly useful if you’re a company or organisation that requires users to save their passwords on your website. When a user saves their password on your site (i.e., on your server), a mechanism occurs that uses a hash function to encrypt the plaintext password (hash input). This generates a hash digest, which your server saves in its password database or list.

There is no way for your workers (or other cybercriminals) to get a hold of a list of your users’ original plaintext passwords stored on your server. The hashing takes place on the server, and they don’t have access to the “initial register” of plaintext data.

This differs from encryption, which encrypts data and then decrypts it using an encryption key and a decryption key. Remember that the purpose of hashing is to prevent the data from being returned to its original plaintext format (i.e., to only be a one-way function). On the other side, with encryption, the aim is for the encrypted data to be decryptable with the correct key (i.e., a two-way function).

That does not, however, imply that passwords are fully safe (even when hashed). This is where the process of salting comes into play, which we’ll go through shortly. But first, let’s look at an example of hashing in reality.

How Does Hashing Work? A Hypothetical Situation

Alice is a dealer whose company loans Bob’s office stationery on credit. She sends Bob an invoice with an inventory list, billing number, and her bank account information after a month. Before submitting the paper to Bob, she adds her digital signature and hashes it. However, when the paper is in transit, Todd, a hacker, intercepts it and replaces Alice’s bank account information with his own.

When Bob’s machine receives the message, it measures the document’s hash value and finds that it varies from the original hash value. Bob’s computer warns him right away that something is wrong with the document and that it is untrustworthy.

Bob would have trusted the document’s content even though it hadn’t been hashed because he knew Alice and the transaction information in the document were real. However, Bob became aware of the change because the hash values did not match. Now he calls Alice and tells her about the details in the paper he got. Alice confirms that her bank account is not the same as the one mentioned in the paper.

A hashing function protects Alice and Bob from financial theft in this way. Consider how this scenario might relate to your own company and how it might help you and your customers avoid being victims of cybercrime.

What Is Salting & Why Do You Use It with Password Hash Functions?

Until hashing, the input values are salted by adding randomly generated characters. It’s a hashing method used in passwords. It distinguishes the hashing values and makes cracking them more difficult. But what difference does it make?

Assume Bob and Alice share the same social media platform password (“Sunshine”). The passwords are stored on the site using SHA-2. Their hash values would be the same since the input value is the same: “8BB0CF6EB9B17D0F7D22B456F121257DC1254E1F01665370476383EA776DF414.”

Let’s imagine a hacker uses malware, brute force attacks, or other sophisticated hash cracking techniques to find out Bob’s password (input value). They will use the same password “Sunshine” to circumvent all other accounts’ authentication mechanisms. They simply need to look at the table of hash values and look for user IDs with the same hash value in their password column.

This is where the use of salt comes in handy. The input values are supplemented with some random alphanumeric characters. Assume Bob’s password has the salt “ABC123” and Alice’s password has the salt “ABC567.” The hash value for the inputs “SunshineABC123” and “SunshineABC567” is stored when the machine saves the password. Even though both original passwords are similar, their hash values are now different due to the salts added. Even if the hacker manages to steal Bob’s password, they won’t be able to enter Alice’s account.

There is a significant distinction between encryption and hashing. Although encryption is a method that uses a key to transform plaintext data into an incomprehensible format, it can also be decrypted using the same or a different key. Hashing, on the other hand, maps your input data to a fixed-length output using a hash function. This is something you won’t be able to recover because it’s basically a one-way operation.

Hash Function Weaknesses

Cryptography’s hash functions, like other technologies and methods, aren’t flawless. There are a number of key points worth noting.

  • There have been instances in the past where common algorithms such as MD5 and SHA-1 generated the same hash value for different data. As a result, the collision-resistance rating was compromised.
  • Hackers use a technique known as “rainbow tables” to try to break unsalted hash values. This is why salting passwords before hashing is so critical for password security.
  • Attackers, security experts, and even government agencies use software services and hardware equipment (dubbed “hash cracking rigs”) to crack hashed passwords.
  • The hashed data can be broken using brute force attacks.

Wrapping Up on the Topic of a Hash Function in Cryptography

In the field of information technology, hashing is a very useful cryptographic method for authentication (verifying digital signatures, file or data integrity, passwords, and so on). In terms of features and implementations for particular purposes, cryptographic hash functions differ. Understanding which hashing algorithms to use (or avoid) in particular contexts is an important part of using hashing.

Cryptographic hash functions, while not flawless, serve as excellent checksums and authentication mechanisms. When a salting technique is used, it can be used to safely store passwords in a way that is too difficult for cybercriminals to invert into anything accessible.


Melina Richardson is a Cyber Security Enthusiast, Security Blogger, Technical Editor, Certified Ethical Hacker, Author at Cybers Guards & w-se. Previously, he worked as a security news reporter.