# What is a key derivation function for dummies?

I’d be happy to explain what a key derivation function (KDF) is in simple terms.

Imagine you have a secret value, like a password, and you need to generate one or more secret keys from it. A key derivation function is a cryptographic algorithm that helps you achieve this. It takes your secret value as input and produces a derived key as output.

Now, you might wonder why we need a KDF in the first place. Well, passwords and secret values are often stored in databases or used to generate private keys for encryption. However, it’s crucial to protect these sensitive values from unauthorized access. If an attacker gains access to the stored passwords or private keys, they can wreak havoc on your security.

Here’s where a KDF comes into play. It ensures that even if an attacker gets hold of the derived key, it would be computationally infeasible for them to reverse-engineer the original secret value. In other words, a KDF adds an extra layer of security by making it difficult to determine the original secret value from its derived key.

Let’s take a look at a simple example to illustrate the concept. Suppose you have a password “MySecretPassword” and you want to generate a private key for encryption. Instead of directly using the password as the key, you can apply a KDF to derive a more secure key.

The KDF takes the password as input and performs multiple iterations of a hash function, which is a mathematical operation that transforms data into a fixed-size string of characters. Each iteration incorporates a salt, which is a random value added to the password to further increase security.

The resulting derived key is a unique and secure string of characters that can be used as the private key for encryption. The important thing to note here is that the derived key is not the same as the original password, but it is derived from it in a secure manner.

There are different types of KDFs available, each with its own strengths and characteristics. Some popular ones include Argon2, Scrypt, and PBKDF2. These KDFs have been extensively researched and are considered secure for various use cases.

To summarize, a key derivation function is a cryptographic algorithm that takes a secret value, like a password, and produces one or more derived keys. It adds an extra layer of security by making it computationally difficult for an attacker to determine the original secret value from its derived key. KDFs are widely used to protect sensitive information and ensure the confidentiality of passwords and private keys.