SHA-256 is a type of “hash function.” A hash function is a mathematical algorithm that takes an input (or ‘message’) and turns it into a fixed-size string of characters, which is typically a hexadecimal number. This string of characters is called the “hash value” or “digest.”
For example, let’s say we have the message “Hello, world!” and we run it through the SHA-256 hash function. The resulting hash value might be “7f83b1657ff1fc53b92dc18148a1d65dfc2d4b1fa3d677284addd200126d9069.”
Now, let’s say we have another message, “Hi, world!” and we run it through the same hash function. The resulting hash value might be “9c1185a5c5e9fc54612808977ee8f548b2258d31.”
As you can see, the two hash values are completely different even though the original messages are only slightly different. This is because the hash function is designed to produce unique hash values for different input messages.
So why do we use hash functions? One reason is to help verify the authenticity of a message. For example, let’s say you download a file from the internet and the website tells you the SHA-256 hash value of the file. You can then run the file through the SHA-256 hash function yourself and compare the resulting hash value to the one provided by the website. If they match, it means the file is authentic and has not been tampered with.
Another reason we use hash functions is for password security. When you create a new password, the website or service you’re using will run your password through a hash function and store the resulting hash value in its database. When you log in and enter your password, the website will run the entered password through the same hash function and compare the resulting hash value to the one stored in its database. If they match, it means you entered the correct password. This way, even if someone hacks into the website’s database and steals the stored hash values, they won’t be able to figure out what the actual passwords are because the hash function is a one-way process (it’s easy to generate a hash value from a message, but it’s practically impossible to generate the original message from the hash value).
SHA-256 (and other SHA algorithms) are preferred for a few reasons:
- Security: SHA-256 is considered to be very secure. It’s a “cryptographic hash function,” which means it’s designed to be very difficult to reverse. In other words, it’s easy to generate a hash value from a message, but it’s practically impossible to generate the original message from the hash value.
- Speed: SHA-256 is also relatively fast, which makes it suitable for use in many different applications.
- Widely used: SHA-256 is widely used and supported. Many different organizations and websites use SHA-256 for things like verifying file integrity and secure communication.
- Collision resistance: A “collision” occurs when two different input messages produce the same hash value. It’s important for a hash function to be collision-resistant, meaning it should be very unlikely that two different input messages will produce the same hash value. SHA-256 is considered to be collision-resistant.
- Hash length: The hash value produced by SHA-256 is 256 bits long, which is why it’s called SHA-256. This means it’s made up of 256 1s and 0s, and is typically represented as a 64-character hexadecimal number.
- Non-reversible: As I mentioned earlier, one of the key features of SHA-256 (and other hash functions) is that it’s a one-way process. It’s easy to generate a hash value from a message, but it’s practically impossible to generate the original message from the hash value. This makes it very difficult for someone to reverse the process and figure out what the original message was.
- Fixed-size output: The output of the SHA-256 function is always the same length (256 bits), no matter how long or short the input message is. This is because the hash function processes the input message in a fixed number of steps, and at each step it combines the input message with a fixed set of numbers and performs a series of mathematical operations.
- Collision attacks: Despite being collision-resistant, it’s still theoretically possible for two different input messages to produce the same hash value (this is called a “collision”). However, it would be extremely difficult and time-consuming to find two input messages that produce the same hash value using SHA-256. There are more advanced hash functions available that are even more resistant to collision attacks, but they are typically slower and less practical to use.
Overall, the combination of security, speed, and widespread use makes SHA-256 a preferred choice for many different applications.
This page was last updated on January 2, 2023.