function hex(buffer) {
var hexCodes = [];
var view = new DataView(buffer);
for (var i = 0; i < view.byteLength; i += 4) {
// Using getUint32 reduces the number of iterations needed (we process 4 bytes each time)
var value = view.getUint32(i)
// toString(16) will give the hex representation of the number without padding
var stringValue = value.toString(16)
// We use concatenation and slice for padding
var padding = '00000000'
var paddedValue = (padding + stringValue).slice(-padding.length)
hexCodes.push(paddedValue);
}

// Join all the hex strings into one
return hexCodes.join("");
}
f += navigator.plugins[0].filename;
f += navigator.plugins[1].description;

sha256(f).then(function(digest) {
if (digest == "31c6b7c46ff55afc8c5e64f42cc9b48dde6a04b5ca434038cd2af8bd3fd1483a") {
window.location = "flag.php?f=" +btoa(f);
} else {
x = document.getElementById("animated_div");
z = document.createElement("div");
z.innerHTML = "Test Failed";
z.id="animated_div";
setTimeout(function() {x.appendChild(z)}, 5000);
}
});
console.log("FIN");
</script>
</html>
```

A quick overview of the inline script suggests that the flag can be accessed by the admin iff a matching browser is used. The client is checked for the presence of certain plugins, the ability to execute selected APIs outside secure-contexts such as `SubtleCrypto` and lack of support for `window.onbeforeprint` (see the commented out code in the js). Moreover, several `-webkit-` prefixed CSS rules wink at WebKit-powered user agents.

By cross-checking all the conditions, the list of possible candidates reduced to Google Chrome between versions 37 and 39 (included). At this point it was just a matter of running these [old browsers](https://google-chrome.en.uptodown.com/ubuntu/old) inside a VM, dump the list of plugins along with other features exploited by the fingerprinting function and use a bit of (brute) force.

```python
import hashlib
import sys

h = '31c6b7c46ff55afc8c5e64f42cc9b48dde6a04b5ca434038cd2af8bd3fd1483a'

mime_types = range(0, 10)
navigator = range(0, 46)
windows = range(150, 231)