Using Custom Blocks in Scratch: Safety Considerations for AP CSP Students

Question

Hey! 👋 I'm a student in AP Computer Science Principles, and we're learning about custom blocks in Scratch. It's super cool, but my teacher keeps mentioning safety concerns. 🤔 Can anyone explain what those are, especially when we're making games and sharing them online?

robert_gaines · Accepted Answer

📚 Understanding Custom Blocks in Scratch

Custom blocks in Scratch are user-defined blocks that extend Scratch's functionality. They allow you to create your own commands, making code more modular and readable. This is a powerful feature, but it also introduces potential safety considerations, especially when AP CSP students are sharing projects online.

📜 History and Background

Scratch, developed by MIT, is designed to be a safe and accessible platform for learning to code. Custom blocks were introduced to allow for more advanced programming techniques. As the platform evolved, so did the understanding of potential risks associated with user-generated content. These risks are mitigated by the platform's moderation and community guidelines.

🔑 Key Principles for Safe Use of Custom Blocks

🛡️Input Validation: Always validate any input received by a custom block. This prevents malicious code injection. For example, if a custom block takes a number as input, ensure it is within an expected range.
🔒Data Sanitization: Sanitize data to prevent cross-site scripting (XSS) attacks. This involves removing or encoding characters that could be interpreted as code.
🌐Privacy Considerations: Be mindful of what data your custom blocks are collecting and sharing. Avoid collecting personally identifiable information (PII) without consent.
⚠️Resource Management: Ensure custom blocks do not consume excessive resources (memory, CPU). Poorly designed blocks can cause performance issues or crashes.
📢Code Review: Encourage students to review each other's code to identify potential security vulnerabilities. This promotes a culture of security awareness.
📝Documentation: Properly document custom blocks, including their inputs, outputs, and any security considerations. This helps others understand and use the blocks safely.
🚫Avoid External Libraries: Limit or avoid the use of external libraries or APIs within custom blocks, as these can introduce security risks. If necessary, carefully vet and monitor any external dependencies.

💡 Real-world Examples

Example 1: Secure Usernames

Suppose you create a custom block to set a username. To ensure safety, you could implement input validation like this:

define set_username (username)
  if <(length of (username)) > [3] and <(length of (username)) < [20]> then
    set [user v] to (username)
  else
    say [Invalid username!] for (2) secs
  end

Example 2: Preventing Infinite Loops

Ensure custom blocks do not create infinite loops that can crash the project. Implement safeguards like maximum iteration counts:

define repeat_until_condition (max_iterations)
  set [count v] to [0]
  repeat until <(condition) or (count) > (max_iterations)>
    // Your code here
    change [count v] by [1]
  end
  if <(count) = (max_iterations)> then
    say [Loop terminated due to max iterations!] for (2) secs
  end

🔑 Conclusion

Custom blocks are a valuable tool for AP CSP students, but safety must be a priority. By following the principles of input validation, data sanitization, resource management, and code review, students can create powerful and safe projects in Scratch. Emphasizing these considerations fosters a security-conscious mindset, preparing students for more advanced programming concepts.