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Comment by sirl1on | Hacker News Reader

You can define a CSP header to only exec 3rd Party scripts with known hashes

But that doesn't make it easy to integrate a new script from an author who doesn't provide the hash already.

Vendor your dependencies. It’s better for you as a maintainer anyway, since caching only works[0] with first party domains with any reliability.

And once you vendor your dependencies you can calculate the hash yourself

[0]: there are caveats to this

How would third party distribution like a cdn affect hashing?

I think https and integrity hashes address two very orthogonal attack vectors.

Because if you're not getting the real benefit (improved response times due to caching) you can stop worrying about hashing it properly or not and simply serve a copy you know to be good (or at least known and probably version controlled). Now you don't need to hash or know which hash is correct or worry about the user getting served the wrong file because someone else got hacked.

Not sure I follow, how does hashing mean you lose improved response times or caching?

Do you mean that hashing the file takes time? I guess that can be significant, but it's probably 2 or 3 cycles per byte, and average js size is like 10kb tops? 30khz doesn't look like much, it's a millionth of a second.

No, the hashing either when generating or checking is very fast like you said. Hashing itself isn't the culprit, but the battle between browsers and those fingerprinting users.

Originally the point of using a shared CDN like this was that if others used it too the file would already be cached on the user's computer and make it even faster. But, this feature was used for fingerprinting users by checking which files from other websites were cached and browsers have isolated the caches in response which makes it impossible to get the speed benefits from before.

So if you're not getting that speed benefit, and only really getting a tiny bandwidth reduction, the risks of serving the file from a 3rd party (which could be mitigated by the hashes) aren't worth it compared to simply vendoring the file and serving it yourself.

So it's not that hashing prevents caching or lowers response times, but that the risk it is mitigating isn't worth the effort. Just 'err on serving the file yourself.

It’s about control foremost. If you vendor your dependencies you know what you’re serving and can calculate the hash and use it in your CSP, and provides more stability for versioning.

Plus, as mentioned, only 1st party origins enjoy any benefits of caching content for faster load times so you get an additional benefit

But you can .. get the hash yourself?

wget url; sha256 file

Of course you can. But when it comes to security, one thing is very important in practice: making the secure way of doing things as easy as possible.

So, why did you not actually post the correct shell script? Apparently that would have been more effort to get right and ensure is correct right? And also work for every OS. And there you have it: if someone first has to figure out which script to run, some percentage will give up here. And that's my point: the browser should make it as easy as possible to avoid that from happening.

Cool. Now your site will break if the upstream pushes a fix while you're on vacation.

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