Re: Subresource Integrity Length Extension?

On 27.01.2014 17:50, Andrew wrote:
> One solution would to be use a HMAC construction where the 'key'
> material is composed from resource meta data, including the verified
> Content-Length, or to mandate a hash function immune to such attacks,
> such as SHA-3.

Thank you for bringing this to our attention.
I actually had someone come up to me yesterday, to raise this very same

It would be an interesting challenge to set oneself, to make a working
lengh extension that not only contains valid JavaScript, but also does
something evil (one could imagine appending "eval(name);//" and then
append some more to fix up the hash - maybe that'll work. But I'd rather
we don't take the chances ;)

So maybe an HMAC makes more sense - who'd pick the key? Is it just
something encoded within the attribute by the website author then?

What do the others think?

Received on Tuesday, 28 January 2014 08:44:26 UTC