3

The general process is to generate a pair of public and private keys and upload the public key to the server for SSH connection.

Then, if I have to manage a large amount of servers, am I supposed to:

  1. Reuse that public key for all servers?

OR

  1. Generate different key pairs for each of those server.

I personally believe the first choice is good enough from the security perspective. Am I correct?

Thanks.

4

The general answer is that you likely will want to put the same personal public key on all servers/accounts you want to login in on. For all practical purposes it's more or less impossible to derive the private key from the corresponding public half.

Then there are a bunch of potential exceptions.

  • While it's normally a good rule to keep the private key passphrase protected that might be less doable while performing certain automated tasks. For that purpose you might also want to have a separate keypair with an unencrypted private key, to use towards those certain (hopefully restricted) accounts.

  • Assuming you mostly connect towards modern enough servers your personal ssh key might be of the ed25519 kind. You might then for compatibility reasons also need a secondary keypair of the RSA kind to be able to login to servers running an older version of OpenSSH. Except that in such a case it's probably good enough to go RSA all the way.

  • If you use ssh agent forwarding a lot there is a theoretical benefit in using separate keypairs, limiting the damage a malicious server can do. Except that I imagine this quickly becoming messy in practice. Probably better then to simply stay away from agent forwarding then.

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