Implementing Secure Pseudorandom Number Generators
Written by  Daisie Team
Published on 8 min read


  1. What are Pseudorandom Number Generators?
  2. PRNGs and security
  3. How to implement a basic PRNG
  4. Security improvements for PRNGs
  5. Implementing a secure PRNG
  6. Verification and validation of PRNGs
  7. Common pitfalls in PRNG implementation
  8. Why secure PRNGs matter

With the ever-increasing interest in online security and encryption, the role of pseudorandom number generators in cryptography has become more significant. These generators, often abbreviated as PRNGs, serve as the heartbeat of many cryptographic systems, ensuring secure and unpredictable data. But you might be wondering, what exactly are these generators and how do they work? Let's dive into the details of PRNGs and understand why they are so important in cryptography.

What are Pseudorandom Number Generators?

At the most basic level, a pseudorandom number generator (PRNG) is a computer program or an algorithm that produces sequences of numbers that only seem random. But here's the catch—they're not really random. They are determined by an initial value known as the seed. If you know this seed, you can predict all the numbers that the PRNG will spit out.

Now, you might be thinking—why use something pseudo-random, why not just use truly random numbers? Well, in many cases, we actually prefer pseudorandomness for a few reasons:

  • Reproducibility: In debugging or testing stages, it's handy to recreate the exact same scenario. With a PRNG, you can do this by using the same seed.
  • Efficiency: Generating true randomness in a computer is a tough job and often slower. PRNGs, on the other hand, can spit out numbers instantly.
  • Control: In some cases, you might want to control how "random" your numbers are. With PRNGs, you can adjust the seed to get the desired effect.

While the concept of PRNGs might seem simple, implementing secure pseudorandom number generators in cryptography is a whole different ball game. It's not just about generating numbers that look random. It's about generating numbers that are unpredictable enough to stand up to potential attackers. And that's where the real challenge lies.

PRNGs and Security

When it comes to cryptography, the security of a PRNG is of utmost importance. Remember, in cryptography, our priority is to keep information secret and safe from prying eyes. But what does it mean for a PRNG to be secure?

A secure PRNG should be able to produce a sequence of numbers that is not only pseudorandom but also unpredictable. That means even if someone knows the entire history of your generated numbers, they still shouldn't be able to guess the next number. That's a tall order, right?

Consider an analogy: Imagine you're playing a game of poker. Now, a predictable deck is like a PRNG with a known seed. If your opponent knows the order of the deck (the seed), they can predict your hand and you'll lose the game. But if your deck is shuffled well (a secure PRNG), your opponent can't predict your hand, no matter how many previous hands they have seen. That's the kind of unpredictability we need from a secure PRNG in cryptography.

But here's the thing: not all PRNGs are created equal. There are many different types, each with its own strengths and weaknesses. The choice of PRNG can have a significant impact on the security of your cryptographic system. So, it's important to understand the basics of how these generators work and how to implement them correctly.

How to Implement a Basic PRNG

Implementing a basic pseudorandom number generator (PRNG) isn't as scary as it might sound. Let's break it down into simple steps, shall we?

First, you need a starting point, also known as a seed. This could be any number, but it's usually the current time. Here's why: the current time is always changing, so it makes for a good unpredictable seed. You could say time is on our side here!

Next, we need a function that takes this seed and turns it into a new number. This is where some math comes in. But don't worry, you don't need to be a math genius to understand this. Think of it like a magic trick where you put a number in, do some mathematical tricks, and voila—a new number comes out!

A common function to use is a linear congruential generator (LCG). Don't let the fancy name intimidate you—it's just a simple formula: (a * seed + c) modulus m. Here, 'a', 'c', and 'm' are constants that you choose. The 'modulus' operation is like a clock: when it reaches 'm', it starts over. It's like magic!

Now, every time you want a new pseudorandom number, you just repeat this process. Take the new number, put it back into the function, and get another new number. It's like a never-ending magic trick!

Remember, this is a very basic PRNG. It's good for understanding the concept, but it's not secure enough for pseudorandom number generators in cryptography. But don't worry, we'll get to the secure stuff later!

Security Improvements for PRNGs

Now that we've dipped our toes into the basics of PRNGs, let's dive into how to make them secure—especially for cryptography. You might ask, "Why bother?" Well, imagine you have a really cool secret and you want to keep it safe. That's where pseudorandom number generators in cryptography come in!

One way to improve security is to use a more complex function. Remember the linear congruential generator (LCG) we talked about earlier? Well, it's a bit like a bike lock. It does the job for a while, but if someone really wants to crack it, they could with enough time and effort. We need something more like a bank vault!

For that, we can use something called a cryptographically secure pseudorandom number generator (CSPRNG). Now, this might sound like a mouthful, but it's not as complicated as it seems. A CSPRNG is a PRNG with properties that make it suitable for use in cryptography. In other words, it's a PRNG that's been working out and is ready to protect your secrets!

One of the properties of a CSPRNG is what's called 'next-bit unpredictability'. This means that even if you know all the previous numbers, you can't predict the next one. It's like a magician who keeps pulling different colored rabbits out of a hat, and you have no idea what color the next rabbit will be!

Another property is 'backtracking resistance'. This means that even if someone gets hold of a later number, they can't figure out the previous ones. It's like trying to follow someone's footprints in the sand, but the waves keep washing them away.

So, while it may take a little more effort to implement a CSPRNG, the security improvements are well worth it. After all, when it comes to keeping secrets safe, you want the best protection you can get!

Implementing a Secure PRNG

Okay, so now you understand what a pseudorandom number generator is and why we need to beef it up for cryptography. Let's roll up our sleeves and figure out how to implement a secure PRNG.

First things first, you need to select an algorithm. There are plenty of algorithms out there, like the Mersenne Twister, which is super popular for its long period and high-quality randomness. Or you might choose the Yarrow algorithm, which is known for its strong security features. It's like choosing a pet; you need to pick one that suits your needs best.

Next, you need to seed your PRNG. Remember, the seed is the starting point of your pseudorandom sequence. It's like planting a tree—the seed you plant determines what kind of fruit you'll get. But here's the catch: if you want your sequence to be unpredictable, you need to make sure your seed is unpredictable too. You could use the current time, or some kind of user input—anything that's hard to guess.

Now, you're ready to generate numbers! With your algorithm and seed in place, your PRNG will start producing a sequence of numbers. But remember, these aren't just any numbers. These are the secret keys to your cryptography castle!

Finally, make sure you periodically reseed your PRNG. This is like changing the locks on your doors every so often. It makes it even harder for anyone to predict your sequence and break into your castle.

And there you have it! You've just implemented a secure PRNG. Feels good, doesn't it?

Verification and Validation of PRNGs

So, you've got your PRNG up and running and it's producing a dazzling array of numbers. But how can you be sure it's doing its job properly? This is where verification and validation come in—sort of like a report card for your PRNG.

Verification is all about making sure your PRNG is working according to the design. It's like checking to see if your pet is performing the tricks you taught it. You could use a variety of tests for this, such as the Diehard tests, which check your PRNG's output against a suite of statistical benchmarks. Or you might use the TestU01 suite, which is a smorgasbord of tests for randomness. Either way, you need to ensure your PRNG is behaving as expected.

Validation, on the other hand, is all about making sure your PRNG suits your needs. It's like making sure your pet is the right fit for your lifestyle. For example, if you're using your PRNG for cryptography, you might want to validate it against the standards set by the National Institute of Standards and Technology (NIST). This will tell you if your PRNG is secure enough for your cryptography needs.

Remember, a PRNG that passes verification and validation is a happy PRNG—and a happy PRNG makes for secure pseudorandom number generators in cryptography.

Common Pitfalls in PRNG Implementation

Let's face it, nobody's perfect. And that includes us when we're trying to implement pseudorandom number generators in cryptography. So, let's talk about some common pitfalls that we might stumble over.

First up is the classic mistake of using a simple PRNG for critical tasks. It's like using a kitchen knife instead of a surgeon's scalpel for an operation. Simple PRNGs, such as the Linear Congruential Generator (LCG), might be easy to implement but they're not secure enough for cryptography. Always pick a PRNG that's up to the job!

Second, is the trap of bad seeding. The seed is the starting point for your PRNG. If you use a predictable seed, like the current time, then your output becomes predictable too. And predictability is a no-no in cryptography. So, make sure your seed is truly random.

Third, is the oversight of not periodically reseeding your PRNG. If you let your PRNG run for too long without a new seed, it might start to cycle or repeat its outputs. And that, my friend, can spell disaster in cryptography.

Finally, there's the pitfall of not testing your PRNG thoroughly. Just because your PRNG looks like it's working fine doesn't mean it is. Always validate and verify your PRNG, as I mentioned in the previous section.

Avoiding these pitfalls can help ensure your PRNG is strong and secure. After all, robust pseudorandom number generators are the backbone of secure cryptography.

Why Secure PRNGs Matter

So, you might be thinking, "Why all this fuss about secure pseudorandom number generators in cryptography?" Well, let me tell you—it's more important than you might think.

Secure PRNGs are like the invisible heroes of the digital world. They're behind many things that you use every day. When you're shopping online and enter your credit card details, it's a secure PRNG that helps keep your information safe. When you're chatting with your friends on a secure messaging app, guess what's helping to keep your conversation private? Yup, it's a secure PRNG.

Okay, so secure PRNGs are important for our daily digital activities. But that's not all. They're also vital for national security. Governments and military organizations around the world use cryptography for secure communications. And you guessed it—secure PRNGs play a key role in that.

So, next time you're implementing a pseudorandom number generator in cryptography, remember its importance. Your work is contributing to a safer and more secure digital world. And that's something to be proud of!

If you're looking to further expand your knowledge on secure pseudorandom number generators and other cryptography concepts, don't miss the workshop 'Crypto For Creators, Part 1: The Backbone Of The Digital Economy' by Tom Glendinning. This workshop will provide you with a strong foundation in understanding the world of cryptography and how it plays an essential role in the digital economy.