4 ms·

I use one key everywhere, but the private key lives on two places only: a usb drive on my keychain and on a backup floppy. When I sit down at a system, I load t

by lutorm 16y ago

I use one key everywhere, but the private key lives on two places only: a usb drive on my keychain and on a backup floppy. When I sit down at a system, I load the key into the agent and then unmount the usb drive. It seems that the only way the private key could be compromised is if someone breaks into the agent when I'm on the machine or if someone spoofs the connection to the agent (which, if I understand correctly, won't give them the key, only the ability to use the key while the agent is running). If the usb drive is lost/stolen, there should be no information that reveals which systems it works on. The key also has a very long passphrase, since I only type it once per day, so that should at least make brute force attacks against the key difficult. This seems like a pretty secure solution to me. What other weaknesses can you think of?

niels_olson 16y ago
encrypt the USB drive's partition?
meastham 16y ago
(which, if I understand correctly, won't give them the key, only the ability to use the key while the agent is running) By design, talking to to the ssh-agent should not give you the decrypted key. However, in reality, anybody that could write to the ssh-agent socket could also ptrace() the agent and find the key in its memory. That would of course require becoming the user you are running ssh-agent as, but that's typically not very difficult. What other weaknesses can you think of? A key logger. Basically, if you don't trust the system you decrypt your key on, all bets are off.
- lutorm 16y ago
  Yeah, talking to the agent on the same system, I agree. But I think the risk of compromising the agent are a lot higher through the forwarded connection (which I use to log into highly populated systems). And I meant that through the connection you shouldn't be able to get the key. The key logger is a good point, but I basically only log in from my laptop, office computer or home computer. Only if one of those three are compromised, as opposed to one of the innumerable machines I log in to, should that be a risk.

by lutorm 16y ago

niels_olson 16y ago

encrypt the USB drive's partition?

meastham 16y ago

(which, if I understand correctly, won't give them the key, only the ability to use the key while the agent is running) By design, talking to to the ssh-agent should not give you the decrypted key. However, in reality, anybody that could write to the ssh-agent socket could also ptrace() the agent and find the key in its memory. That would of course require becoming the user you are running ssh-agent as, but that's typically not very difficult. What other weaknesses can you think of? A key logger. Basically, if you don't trust the system you decrypt your key on, all bets are off.

lutorm 16y ago
Yeah, talking to the agent on the same system, I agree. But I think the risk of compromising the agent are a lot higher through the forwarded connection (which I use to log into highly populated systems). And I meant that through the connection you shouldn't be able to get the key. The key logger is a good point, but I basically only log in from my laptop, office computer or home computer. Only if one of those three are compromised, as opposed to one of the innumerable machines I log in to, should that be a risk.