Posts tagged JavaScript

Subresource Integrity for JavaScript

Including JavaScript files from a CDN can be beneficial in many ways as you don’t have to ship the code with your code and caching can be done by the browser of a proxy server. It also allows for injecting untrusted code into a web page as someone else is hosting the code you rely on. But Firefox, Chrome, and Opera already support Subresource Integrity checking script and link tags. Hopefully, both Safari and Edge (or Internet Explorer) will support it soon.

But how does it work? First, let’s calculate the SHA256 hash of JQuery version 3.2.1 hosted by Cloudflare. Also, keep in mind to verify this number with the official version offered by JQuery. In this example, we download the minimized version of JQuery with curl and run it twice through OpenSSL to generate the checksum and encode the result in base64 format.

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