Licensing

How to Generate Secure License Keys for Software Evaluation and Distribution

In today’s software landscape, allowing potential customers to try your software before making a purchase is a common practice. However, you also want to protect your intellectual property and prevent unauthorized copying or distribution. One effective way to achieve this is through software evaluation licensing, particularly by implementing a well-designed license key system.

The Challenge of Software Evaluation Licensing

When distributing your software, you might face several challenges, including:

  • Allowing users to evaluate the software without making it freely available.
  • Preventing unauthorized copies and ensuring the software is used only by the intended license holder.
  • Incorporating details into the license keys, such as expiration date and user-specific configurations (like the MAC address).

To tackle this problem, it’s important to construct a license key that can effectively encapsulate these requirements while remaining user-friendly.

Creating a License Key System: A Step-by-Step Guide

1. Define the Information to Include

First, decide what information needs to be embedded within the license key. Commonly included details are:

  • MAC Address: Ties the software to a specific machine.
  • Expiration Date: Sets the validity period for the license.
  • Additional Restrictions: Any other limitations you envision (e.g., usage limits, feature sets).

2. Hashing for Security

One way to generate a secure license key is by using a hashing algorithm. While there are many hash functions available, we recommend using MD5 for this purpose. Although it isn’t the most secure hashing algorithm, it is sufficient to deter casual attacks.

Here’s how to implement this step:

  • Combine the chosen information (like MAC address and expiration date) into a single string.
  • Hash this string using MD5.
  • Extract the first ‘X’ characters from the hash to form the key. Choose ‘X’ based on the desired length of the key.

3. Formatting the License Key

The structure of the license key can include both the hashed portion and the plain information. This mixture allows for easy verification while preventing users from tampering with the critical details.

Here’s a simple example of how a license key file might look:

# License key for XYZZY
expiry-date=2009-01-01
other-info=blah
key=[md5 hash of MAC address, expiry date, other-info]

4. Optional Obfuscation

While the hash will prevent most users from changing crucial details like the expiration date, consider including the expiration date and other information in a slightly obfuscated format within the key. This makes it more challenging for a casual user to modify the key without breaking its functionality.

Conclusion

By following the steps outlined above, you can implement an effective license key system for your software. This not only allows potential customers to evaluate your products confidently but also safeguards your software against unauthorized distribution and use. Remember, while no system is foolproof, you can implement changes that deter casual misuse and foster a more secure distribution model.

With these strategies in hand, you’re well on your way to successfully navigating the landscape of software evaluation licensing!