What is the SHA-256 algorithm, and how does it work?

While we spend a lot of time talking about encryption, SHA-256 deserves its rightful place in the Mount Olympus of cybersecurity. Here’s why hashing and the SHA algorithm in particular are so important.

SHA stands for Secure Hashing Algorithm, and it is a family of cryptographic hash functions developed by the National Security Agency (NSA) in the United States. A hash function, in simple terms, is a mathematical algorithm that takes an input (any data, like a file or a password) and produces a fixed-size string of characters, which is the hash value or digest. But keep in mind that it is not encryption. To know how they differ, check our hashing vs encryption comparison.

SHA-256 is the successor of SHA-1, a widely popular algorithm in the past. However, it has since been deemed insecure due to vulnerabilities discovered in its code. As technology advanced and computing power increased, it became easier for attackers to exploit these weaknesses and compromise the integrity of hashed data.

SHA-256 refers to the bit size of the hash output. In other words, the resulting hash value from SHA-256 is 256 bits long, which provides a significantly larger search space compared to its predecessor, making it computationally infeasible to reverse engineer the original input from the hash value.

You can think of SHA-256 as your favorite sauce made by blending and mixing vegetables and spices. While you can’t tell what’s in there exactly (unless you check the label) — every time you taste it, you know it’s the sauce you love so much.

SHA-256 takes words and symbols and blends them up just like your favorite sauce maker. If the words and symbols are the same, the 256-bit long hash would be the same, too. But if you change one little detail, the output will be different.

Hashing algorithms like SHA-256 can take short passwords and 100,000-word e-books and pass them through a number of complex steps to produce a 256-bit hash value.

SHA-256 plays a pivotal role in ensuring data security, ranging from protecting a blockchain wallet to helping store user passwords and digital signatures. Here are its most common uses:

Digital signatures

In the realm of digital signatures, SHA-256 can ensure the integrity and authenticity of documents and messages. For example, SHA-256 generates a hash value from the content being signed, acting as a unique digital fingerprint. The signer’s private key is then used to encrypt the hash value, creating the digital signature.

On the recipient’s end, a program can decrypt the signature using the corresponding public key and compute the hash value of the document.

Password hashing

One of the most popular SHA-256 uses is password hashing. Instead of storing the actual passwords, companies derive their hash values instead. It’s much safer for the user. Every time you enter your password, the system derives a new hash value and checks if it matches with the one stored on the database.

Blockchain technology

The emerging blockchain technologies also use SHA-256 to secure the integrity and immutability of data stored in blocks. Because each block in a blockchain contains a unique digital fingerprint, nobody can change the contents of the block without changing their hashes. In other words, by linking blocks using their hash values, the blockchain creates a transparent and tamper-proof ledger that anyone can verify.

File integrity

Hashing can help protect the integrity of any file —- documents, videos, software executables, you name it. It’s important because whether you need to sign a contract you’ve been working on for weeks or update a piece of software, you can verify that in neither case the file has been tampered with.

SSL/TLS certificates

We’re not here to debate the differences between TLS vs SSL. Just know that hash functions such as SHA help make your browsing better, even if you’re already using a VPN. SHA-256 can help secure SSL/TLS (Transport Layer Security) certificates by creating a digital signature your device can verify. For example, when a server presents its TLS certificate to clients such as web browsers, the client can then use the corresponding public key to decrypt and verify the signature. If the SSL certificate was not issued by a trusted certificate authority or has been tampered with, the hash values wouldn’t match.

Sometimes, hashing terminology can be a bit tricky. Let’s go over a view terms you should know to fully understand how SHA-256 works:

Rounds

A round is a sequence of operations performed multiple times to thoroughly mix up the data until it’s unrecognizable. This process is repeated 64 times within the SHA-256.

Shift amount

The concept of a shift amount is used as a consistent technique for rearranging bits. The data blocks are partitioned into eight portions, each consisting of 32 bits. These eight segments are subsequently shifted in a specific manner, effectively shuffling and randomizing the data.

Additive constants

In SHA-256, specific values known as additive constants are incorporated into the data blocks. There are 64 such constants involved in this process. These round constants are derived from the cube roots of the first 64 prime numbers. Notably, only the initial 32 bits of these fractional values are utilized.

We’ve covered a lot of ground today and, hopefully, it explains why SHA-256 is important. There are a few more advantages we haven’t talked about yet. SHA-256 is versatile and easy to implement in a variety of settings. It’s also really hard to break. For example, hashing algorithms should be irreversible, but aren’t always. SHA-256 is strong enough to prevent hackers from deriving the original message from the hash value.

Hashing can also help you fight off a cybersecurity attack. For example, if you had to defend against a DDoS attack, you could use SHA-256 to authenticate and verify the integrity of incoming network traffic.

When it comes to disadvantages, SHA-256 is slower and more resource intensive than the previous versions. Some researchers also claim that in the future, SHA-256 may be vulnerable to brute-force attacks.

Many consider SHA-256 to be one of the most secure hashing algorithms today. This is because it’s great at preventing values from being reversed back to the original content. Another problem that it solves well is avoiding hashing collisions. This means that two separate inputs cannot produce an identical hash. Lastly, secure hashing algorithms must ensure that values are different enough so nobody could tell that two hashes come from a similar data. SHA-256 is great at all three tasks.