Content Security Policy (CSP) is a powerful security feature that helps protect websites from malicious attacks like Cross-Site Scripting (XSS). One challenge with CSP is allowing legitimate inline scripts while blocking malicious ones. CSP hashes provide an effective solution to this problem.
What Are CSP Hashes?
CSP hashes are cryptographic hashes of inline scripts. When you add a hash to your CSP, browsers will execute inline scripts only if their content matches the specified hash. This allows you to permit specific inline scripts without enabling all inline code, enhancing security.
How to Generate CSP Hashes
Generating hashes involves hashing the exact content of your inline scripts. Common algorithms include SHA-256, SHA-384, and SHA-512. Here's a simple process:
- Copy the inline script content.
- Use a hashing tool or command-line utility (like OpenSSL) to generate the hash.
- Include the hash in your CSP header.
For example, using OpenSSL:
echo -n "<script content>" | openssl dgst -sha256 -b64
Implementing CSP Hashes in Your Website
Once you have your hash, add it to your Content Security Policy. For example, in your HTTP headers:
Content-Security-Policy: script-src 'self' 'sha256-...' ;
Example
If your inline script is:
<script>console.log('Hello, world!');</script>
And the hash generated is:
'sha256-XxYz...'
You would include it in your CSP header like this:
Content-Security-Policy: script-src 'self' 'sha256-XxYz...';
Best Practices and Tips
- Always generate hashes from the exact script content.
- Update hashes if you modify inline scripts.
- Combine hashes with other CSP directives for comprehensive security.
- Test your CSP policies thoroughly to avoid blocking legitimate scripts.
Using CSP hashes effectively balances security and functionality, allowing legitimate inline scripts while blocking malicious content. Proper implementation and testing are key to maintaining a secure website.