Updated: Never — Philip's Blog

Wouter blogs about how you can SSH with your Belgian eID card.

Unfortunately, he fails to mention that this is a very bad idea because the cards cannot be trusted.

The private key on the card has been generated by an entity that is not you and which you cannot trust for this purpose. You cannot be reasonably sure that no clandestine unencrypted copies of your private key exist under government control or under the control of a disgruntled government employee or contractor.

Rule #1 of healthy use of cryptography: generate your own keys. Trust nobody.

Do you really want to allow the government to ssh to your machine? Or the disgruntled government employee who incidently, can already impersonate you to buy a house?

If the system generating the private keys is compromised in any way, any users of the cards are fucked (to put it mildly). Your private key is "you" in a number of ways that matter quite a lot.

What about certificate revocation lists (CRLs)? I hear you cry.

Rule #2 of healthy use of cryptography: nobody ever checks CRLs. To rely on them is foolish.

Wouter's example demonstrates this rather nicely: the public key is copied to the authorized_keys file on the server directly. No CRL will ever be checked. An entry in a revocation list which is never checked will not prevent the compromised key from being used to authenticate against the system.

If any of the above scares you (which it should) I highly recommend you get the certificates on your eID revoked. Preferably, you should revoke the certificates as soon as you go to collect your eID.

Of course, revocation does not protect you against clandestine copies of the private key. Make sure you get the authority you ask to revoke your keys to sign a dated piece of paper so you can prove this later if a clandestine copy of your key is used to impersonate you.

Am I being paranoid?

Yes!

Why?

How do you feel about your "identity" being replaced by a private key which you did not generate and which you don't control? I find it incredibly scary.