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Comment by weichi | Hacker News Reader

Very interesting article. But it makes we wonder ... if someone gets access to your key file, that's nearly always going to be because they have access to your login account, right? And at that point isn't the gig pretty much up?

In other words, how much additional security does password-protecting your private key gain you?

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It provides some security against attackers that aren't capable of subtlety. If yank your unencrypted hard drive out and walk away with it in my pocket I can't use your encrypted SSH key to impersonate you to other machines unless I can break the passphrase.

If your HDD is stolen they can plug it into another computer and copy any file they want.

They would get quite a few pseudorandom numbers of mine, aside from a self-compiled Linux kernel. :-)

> aside from a self-compiled Linux kernel.

Likely sitting on an unencrypted /boot, waiting to be replaced by one with a keylogger, am I right? Of course a sane person doesn't trust a system that's been compromised before nuking it and reloading from a clean image.

There is unfortunately relatively little you can do to thwart such an attack, apart from keeping your notebook with you at all/most times.

Though using a USB key for /boot might be an idea, it is a little less clunky than a ThinkPad and since I suspend to RAM most of the time, it could even be practical. Hm.

Can't TPM be used for this? It could verify your /boot with keys external to the disk itself. I'm not sure if somebody has actually built a solution that uses it yet.

https://en.wikipedia.org/wiki/Trusted_Platform_Module

It could (the same goes for Secure Boot, in some sense). But the three-letter agencies from whom you want to protect yourself here likely have backdoor keys</paranoia>.

Sure it can, as can its evolution in the form of UEFI's Secure Boot, the problem is everyone wants to label these as technologies to enable lock-in instead of technologies to provide a trusted boot chain to ensure your system isn't compromised.

Creating multiple SSH keys is an interesting form of obfuscation, but it relies on trimming your bash command history and not using ssh-config files.

> In other words, how much additional security does password-protecting your private key gain you?

Someone took your laptop, they could now have one of two things:

(a) - Just your laptop

(b) - your laptop and every server you're using your key for access to.

b is prevented by the passphrase.

No, I think more like one of three things:

a) just your laptop, b) your laptop and all files, or c) your laptop and all your files, and access to servers as per above.

I like "a" the best, and it's achieved through full-disk encryption. You don't even need a new passphrase for that, considering that you probably already password-protect your computer.

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