3 ms·
> Fortunately, as long as the proxy doesn’t have the original server’s private key, then the key fingerprint will be different. Will it? What is the proxy serv
by deathanatos 11y ago
> Fortunately, as long as the proxy doesn’t have the original server’s private key, then the key fingerprint will be different.
Will it? What is the proxy server happens to have a key whose fingerprint hash is the same as the original server's key?
SSH very recently upgraded how keys are fingerprinted; the screenshots in this article are the old method, which as I learned recently, are MD5 hashes. (I had thought they were SHA1.) SHA-256 is what gets used now. But, for example, Ubuntu's LTS doesn't have the update. I'm glad they made the change, but I'm left wondering how key exchanges aren't somewhat vulnerable on unupgraded machines.
(e.g., fingerprints now look like:
SHA256:7h5Q0O1Qc8G7Hv/hVIrx1d6ZTgnITwrutr1XDBYY0sg
)
- sargun 11y agoI'm not sure how easy it is to forge a fingerprint. Given most of the MD5 collision work was done based on length-extension attacks, I think SSH is somewhat more tolerant to these. Nonetheless, your point stands - it is possible to forge a key that has the same fingerprint as the original server, but I cannot think of any practical way to do this.
- userbinator 11y agoNonetheless, your point stands - it is possible to forge a key that has the same fingerprint as the original server, but I cannot think of any practical way to do this. If I understand correctly that's basically a preimage attack, and even for MD5 where you can find arbitrary colliding pairs very easily today, AFAIK no one has come up with a single preimage example or practical attack.
- TillE 11y agoRight, none of the published MD5 attacks allow you to generate data to match a specific hash value. It's certainly a good idea to avoid MD5, but it's not easily exploitable in most situations.