Key Derivation Functions: Best Practices & Tips
Written by  Daisie Team
Published on 7 min read


When you're dealing with cybersecurity, it's crucial to understand key derivation functions. This blog will simplify the concept, offer best practices, and provide tips to ensure you're utilizing these functions effectively. So, whether you're a seasoned coder or just starting out, we'll walk you through everything you need to know about key derivation functions to boost your security game.

What are Key Derivation Functions?

Key Derivation Functions (KDFs) are like skilled locksmiths in the digital world. They take an input—think of it as a chunk of raw metal—and pass it through a specific process to create a secure key. The input could be a password or another piece of sensitive data. It's similar to how a locksmith would fashion a key from a block of metal. The purpose of a KDF is to create a key that's tough to crack, enhancing the security of your data.

To understand key derivation functions, let's break it down a bit:

  • Input: The raw material, which could be a password or some other data. This is what the KDF will transform into a secure key.
  • Process: This is the specific function the KDF uses to transform the input. It's a bit like the locksmith's tools and techniques.
  • Output: The secure keying material produced by the KDF. Like a well-crafted key, this is designed to be hard for hackers to replicate or guess.

Key derivation functions are not a one-size-fits-all solution. There are different types, with the most common being hash-based key derivation functions. But don't fret—we'll get into that a bit later on.

Now that you have a basic understanding of key derivation functions, let's explore how they're used in real-world scenarios.

Key Derivation Function Use Cases

Picture this: you've just bought a brand new padlock, but it came with no keys. Instead, there's a blueprint that a locksmith can use to create a key specifically for your lock. In this scenario, the blueprint is like a key derivation function. It takes a 'seed' (like our password) and creates a key that fits our metaphorical padlock.

So, what happens when we apply this to the digital world? Let's take a look at some common scenarios.

  1. Creating Secure Passwords: One of the most common uses of KDFs is in the creation of secure passwords. A KDF takes a user's password and transforms it into a unique, complex password. It's like taking a simple house key and turning it into a highly secure, impossible-to-duplicate key for a safe. This is essential in today's world, where cyber threats are lurking around every corner.
  2. Encrypting Data: KDFs are also used to encrypt data. When you're sending sensitive information across the internet, you don't want it to be intercepted and read by unauthorized parties. To prevent this, KDFs can be used to generate encryption keys, which scramble the data so it can't be read unless you have the key to unscramble it.
  3. Securing Wireless Networks: Wi-Fi networks use KDFs too. When you enter a password to connect to a Wi-Fi network, a KDF takes that password and turns it into a complex key. This key is used to encrypt the data transmitted between your device and the Wi-Fi router, preventing others from snooping on your connection.

But remember, like a locksmith, a key derivation function is only as good as the input it's given. A weak password or input can still lead to a weak key, no matter how good your KDF is. So always ensure your inputs are strong to get the most out of your key derivation functions.

Best Practices for Using Key Derivation Functions

Now that we've covered what key derivation functions are and some of their use cases, let's talk about how to use them correctly. Here are some handy tips to help you make the most of your KDFs.

  1. Use a Strong Seed: The seed is the starting point for your key derivation function. It's like the ingredients in a recipe— if you start with low-quality ingredients, you're not going to end up with a top-notch dish. So, always use a strong, unique seed for your KDF.
  2. Choose a Suitable KDF: Not all KDFs are created equal. Some are better suited for certain tasks than others. For instance, PBKDF2 is great for password hashing, while HKDF is excellent for creating keys for encryption. It's important to understand key derivation functions and their strengths to choose the right one for your needs.
  3. Update Your KDFs Regularly: Just like your phone's software, KDFs need updates too. As technology advances, so do the methods used by hackers. Keeping your KDFs updated ensures they're equipped with the latest security features to protect your data.
  4. Limit the Number of Guesses: If someone is trying to crack your derived key, they'll most likely do it by guessing. By limiting the number of guesses, you can make this process incredibly time-consuming and impractical for the attacker.

By following these best practices, you can ensure that you're using key derivation functions effectively and securely. Always remember, understanding key derivation functions is a journey, not a destination— there's always more to learn!

How to Securely Implement Key Derivation Functions

So, you've decided to implement a key derivation function. Good for you! But how do you do it securely? Here are a few steps to guide you through the process.

  1. Choose a Reliable Cryptographic Library: Your first step should be to find a solid cryptographic library that supports the KDF you've chosen. This library should be well established and widely used in the community, ensuring its reliability.
  2. Set Up a Strong Seed: We've talked about the importance of a strong seed before. When implementing a KDF, it's vital to use a unique and random seed. This seed is your first line of defense against attackers.
  3. Configure Your KDF Properly: Key derivation functions often come with a range of configurable options. It's important to understand these options and how they affect your KDF. For example, increasing the number of iterations can enhance security but also requires more computational resources.
  4. Test Your Implementation: Never assume your implementation works perfectly. Always test it thoroughly to ensure it functions as expected. This includes testing edge cases and potential failure points.

Remember, the goal here is to understand key derivation functions and how to implement them securely. It's not about rushing through and ticking off boxes. Take your time, do your research, and always prioritize security over convenience.

Key Derivation Functions and Password Storage

Let's talk about another important application of key derivation functions — password storage. You might be thinking, "Why do we need to use KDFs for storing passwords?" Well, storing passwords in plain text is a big no-no, and even hashed passwords can be vulnerable to attacks. Here's where KDFs come in.

  1. Hashing vs. Key Derivation: While hashing creates a unique output from an input, KDFs go a step further. They add a salt (a random value) to the input, which drastically reduces the risk of brute force and rainbow table attacks. This makes KDFs a much safer option for storing passwords.
  2. Adding Work Factors: KDFs also introduce work factors like computational cost and memory usage. It means an attacker has to spend more resources to crack each password, making attacks less feasible.
  3. Upgrading Legacy Systems: If you're dealing with a system that used to store passwords as hashes, you can upgrade it to use a KDF. You don't even need to ask users to change their passwords. When users log in, you can take their password, run it through the KDF, and replace the old hash with the new derived key.

So, if you're looking to understand key derivation functions better, consider how they can help with password storage. It's a practical application that showcases their strengths and benefits.

Tips for Choosing the Right Key Derivation Function

Choosing the right key derivation function can feel like a daunting task, especially if you're new to this. But don't worry, we've got some simple tips to help you make the right choice.

  1. Understand Your Needs: The first step is to understand why you need a KDF. Are you trying to secure passwords, generate keys for encryption, or something else? The use case will guide your choice.
  2. Consider the Work Factor: Different KDFs have different work factors — computational cost and memory usage. If you're using a KDF for password storage, you might want a high work factor to discourage brute force attacks. But if you're generating keys for a real-time system, a high work factor might slow things down too much.
  3. Check the Standard: Some KDFs, like PBKDF2 and Scrypt, are widely recognized and have been around for years. They're tested, trusted, and have a lot of documentation. But don't just go for the most popular one — make sure it fits your needs.
  4. Ask for Help: If you're still not sure, don't hesitate to ask for help. There are plenty of forums and communities where you can get advice from people who understand key derivation functions well.

Remember, there's no one-size-fits-all when it comes to KDFs. The best choice depends on your specific situation and needs.

Common Mistakes to Avoid in Key Derivation

As you get ready to dive into the world of key derivation functions, it's important to be aware of some common pitfalls. Here's a short list of mistakes to avoid:

  1. Using Weak Passwords: Even the strongest key derivation function can't protect a weak password. No matter what KDF you use, always enforce strong password policies.
  2. Ignoring Updates: KDFs evolve over time, with updates fixing bugs and improving security. If you're using an outdated KDF, you're not getting the best protection possible. So, always keep your KDFs up to date.
  3. Skipping the Salt: Salting is a key step in key derivation, adding an extra layer of security. If you skip the salt, you're making it easier for attackers to crack your keys.
  4. Reusing Keys: Reusing keys is a big no-no. If one key gets compromised, all data encrypted with that key is at risk. Always generate a new key for each session or user.

Remember, understanding key derivation functions is only part of the battle. You also need to use them correctly to keep your data safe and secure.

If you're interested in learning more about key derivation functions and wish to dive deeper into cryptography best practices, check out the workshop 'Crypto For Creators, Part 1: The Backbone Of The Digital Economy' by Tom Glendinning. This workshop offers a comprehensive understanding of the role cryptography plays in the digital economy, and it will help you grasp the importance of key derivation functions in securing your digital assets.