Building a Blackjack Game: Logic, Design, and Cryptographic Fairness

Lxne - December 18, 2024

Blackjack is one of the most popular casino games worldwide, known for its simplicity, fast-paced gameplay, and high RTP (Return to Player). The RTP represents the percentage of all wagered money a game is expected to pay back to players over time. In Blackjack, this number can reach 99% or higher when played with optimal strategy, making it one of the fairest games in the casino world.

In this post, I'll walk you through the process of building my online Blackjack game — from game logic and card-shuffling algorithms to user interface design and cryptographic fairness.

Why Blackjack?

Blackjack was an easy pick for my online casino project. It's a game that's simple and fun for everyone, offering a great balance of luck and strategy. I've played Blackjack many times with friends and family (without real wagers), so I already knew the rules well. My goal was to create a classic Blackjack experience using the standard 6-8 decks of cards, just like you'd find in a real casino.

Game Rules & Mechanics

Staying true to the game's classic rules, I implemented Blackjack based on standard casino gameplay. Here's how the game works:

  • Dealer Stands on Soft 17: If the dealer has a hand valued at 17 with an Ace counted as 11 (a "soft 17"), they must stand.
  • Blackjack Pays 3:2: A natural Blackjack (an Ace plus a 10-value card) pays 3:2, meaning a $10 bet returns $15.
  • Insurance Option: If the dealer's face-up card is an Ace, players can choose insurance to hedge against the dealer having a Blackjack.
  • Split and Double Down: Players can split pairs into two separate hands or double down after receiving their first two cards.
  • No Surrender or Card Swap: I decided not to implement surrender or card-swapping mechanics, keeping the experience as authentic as possible.

In the event of a tie (a “push”), the player's bet is returned with no win or loss — just like in a real casino.

Design & Visual Style

When designing the game, I wanted to keep the interface clean and simple. I used CSS animations for smooth interactions and even added a custom logo on the back of the cards for branding.

To enhance the experience, I added intuitive animations for dealing cards, where cards are dealt as if from a real card shoe which is typically located to the dealer's left. When a player wins, green outlines appear around their cards, while a red outline highlights losing hands. These small touches make the game more immersive while keeping the design uncluttered.

Core Logic & Game Mechanics

Implementing the game logic required handling many complex mechanics behind the scenes.

Shuffling & Randomness

The most critical part of Blackjack is ensuring the deck is shuffled fairly. I used cryptographically secure random number generation combined with the Fisher-Yates Shuffle algorithm. This guarantees the deck is shuffled in an unpredictable and provably fair way.

Hand Evaluation

Building the logic to evaluate players' and the dealer's hands was challenging. I wrote an algorithm that checks each hand for:

  • Hard and Soft Hands: Correctly counting hands with Aces as 1 or 11.
  • Pairs for Splitting: Detecting identical cards to enable splitting.
  • Blackjack Detection: Checking if the player or dealer has a natural Blackjack.

The dealer's decision-making logic was straightforward: the dealer hits until reaching soft 17 or higher, following standard Blackjack rules.

User Interaction & Betting System

Players can interact with the game using simple controls:

  • Hit: Take another card.
  • Stand: Keep the current hand.
  • Double Down: Double the bet and receive only one additional card.
  • Split: Split a pair into two separate hands.
  • Insurance: Place a side bet when the dealer shows an Ace.

To make betting easy, I added a feature where players can enter their bet amount manually or use buttons to double or halve the bet. This allows for strategies like the Martingale System, where players double their bet after every loss to recover past losses with a single win.

Fair Play with Cryptographic Verification

Fairness is a core feature of my Blackjack game. The deck is shuffled using cryptographic randomness with a secret server seed. Once the entire deck has been used, the seed and final deck order are revealed to the player, enabling them to verify that the shuffle was fair.

Here's how Provably Fair Shuffling works:

  • Server Seed: The platform generates a hidden server seed before shuffling.
  • Deck Shuffle: The cards are shuffled using the server seed and cryptographically random numbers.
  • Verification: After the game, players can check the initial deck order by comparing it with the revealed server seed, ensuring the shuffle wasn't manipulated.

Challenges & Lessons Learned

The most difficult part of developing the game was writing the hand evaluation algorithm, especially when distinguishing between hard and soft hands involving Aces. Since an Ace can count as either 1 or 11, keeping the total hand value accurate required precise logic.

The best way to debug and refine the game logic was by playing the game repeatedly to catch edge cases and ensure all scenarios were accounted for.

This project taught me a lot about front-end design — an area I hadn't focused on much before. From animations and card designs to interface usability, I learned how to build a visually engaging game that's still functional and intuitive.

Final Thoughts

Looking back, I'm extremely happy with the outcome. If I were to revisit the project, the only thing I'd change would be refactoring the code to make it even cleaner and more modular. But as a whole, the project came together just as I envisioned — a simple, fair, and immersive Blackjack game with solid gameplay mechanics and an elegant design.

Building this game was a rewarding experience, and I look forward to applying everything I've learned to future projects.