RC5 is a fascinating encryption algorithm that’s all about flexibility and simplicity. Let’s dive into what makes it tick:

🔐 What Is RC5?

RC5 (Rivest Cipher 5) is a symmetric-key block cipher developed by Ronald Rivest in 1994. It’s known for being:

• Simple to implement
• Fast on both hardware and software
• Highly customizable in terms of block size, key length, and number of rounds

⚙️ Key Features

• Block Size: Can be 32, 64, or 128 bits (64 bits is common)
• Key Length: Variable—up to 2040 bits!
• Rounds: Adjustable from 0 to 255 (12 rounds is typical)
• Structure: Feistel-like network using basic operations:
  • Bitwise XOR
  • Modular addition
  • Data-dependent rotations

🔄 How RC5 Works (Simplified)

1. Key Expansion: The user’s key is expanded into a set of subkeys using mathematical constants (like e and the golden ratio).
2. Encryption:
   • The plaintext is split into two halves.
   • Each round mixes the halves using XOR, addition, and rotations.
   • Subkeys are applied at each step to scramble the data.
3. Decryption: Follows the same steps in reverse using the same subkeys.

🛡️ Strengths

• Speed: Uses simple operations that are fast on most processors.
• Flexibility: You can tune it for performance or security.
• Compact: Requires minimal memory—great for embedded systems.

⚠️ Weaknesses

• Security Depends on Parameters: Fewer rounds or shorter keys can make it vulnerable.
• Some Attacks: Certain configurations (like 12-round RC5 with 64-bit blocks) are susceptible to differential attacks.