This looks impressive.
Is an MD5 hash still "safe" if you use a salt? Can an attacker generate a collision having the MD5 hash without knowing the salt?
Is an MD5 hash still "safe" if you use a salt? Can an attacker generate a collision having the MD5 hash without knowing the salt?
You should still use a different hash algorithm though.
Developer writes some code and publishes it. It's big, so he puts it on an untrusted CDN, and also publishes an MD5 hash of the code (not via the CDN).
User downloads the code from the CDN, and verifies the published hash matches.
A malicious CDN couldn't make an evil file with a matching hash, based on known attacks against MD5, unless they could influence the Developer to get certain data into the original file.
Then the CDN, by definition, would control the data that the end-user (downloader) hashes.
But I understand the confusion: londons_explore meant to write "there are no known (practical) preimage attacks" against MD5, which is true, since the only theoretical preimage has a complexity 2^123 or so.
I _think_ that would do it though, if your salt is private and secure enough and you apply it the right way. I easily could be missing an attack though, so take with a large grain of salt (heh).
Depending on how the salt is applied, yes.
Great work btw!
> I can retroactively adjust the hex digits in the image without affecting the resultant hash
My point is: I give you a hash H, can you generate a collision by finding a string X, so that when I append an (unknown to you) salt S then MD5(X + S) = H.
EDIT: To make it clear, the only feedback you get when you try X is whether the final hash matches, you don't get the resulting hash each time.
What you can do trivially is find 2 strings X1 and X2 such that md5(X1) == md5(X2). In this case seeding the way you described won't help because md5(X1+S) will equal md5(X2+S) due to the way MD5 works