Ask HN: One SSH key or many SSH keys? | Hacker News Reader

Ask HN: One SSH key or many SSH keys?

4 pointshtunnicliff6 comments

Is there any benefit to using multiple, separate keys to authenticate to different resources versus only using a single SSH key?

On one hand, I've heard that an SSH key is supposed to represent an identity, so using your "identity" everywhere makes sense.

On the other hand, I've heard that keeping SSH keys separate is important in the same way using separate passwords for different resources is important.

What do you all think?

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I use a distinct key for each remote account. Although it's meant to be infeasible to infer a private key from a public key, distinct keys give me another layer of defence in depth in case an attacker ever finds a way to do it. Another advantage is that I can use passphrases selectively. For example, if I have an unpriviledged remote account with shell access disabled because it's used only for proxy tunnelling, it's less important to have a passphrase protecting its key than it would be for a remote root account, and not having one could be more convenient.

It is not exactly like using the same password in multiple sites because you just need one remote site that stores your password in plain text or simple enough to reverse to compromise all the accounts that use the same password. For asymmetric encryption is the private part the one that should be safe (assuming the right algorithms) and just you should have access to it. If someone/something else can access/use them directly or indirectly then they may get compromised. And that may be a guide on why having multiple certificates, because you can discriminate with passphrases against i.e. local agents.

One per device seems a good rule of thumb. If you have 2 laptops, each gets a diff ssh key, and then you config both in github/server(s).

It's slightly more painful to setup, but you get more flexibility later on in case you loose one key you have the other, and in case you need to cancel just one you can.

If you use hardware security keys, you get one per device naturally.

Second that. By means of which ssh key was compromised you get an answer of which of your devices need formatting.

I prefer three: one for particularly important projects, one for normal projects, and one where security isn't a major concern.

I like using short-lived SSH certificates, and avoiding long-lived keypairs entirely.

Vendor post but it summarises the operational and security problems well.

https://smallstep.com/blog/use-ssh-certificates/

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