I understand exactly how it works. How do you get a code-signing paradigm down to something as simple as curl | sh though? (Well not as simple, but still a human-readable one-liner that works on nearly all Linux systems.)
I thought maybe a single-line invocation might piggy-back on SSL as follows:
- get a server's public key that is not online or able to answer requests (because if it were it couldn't be airgapped)
- but still use the key to verify the script that's downloaded from the server that is online.
- only pass the code to sh if it was properly signed by the offline server.
Then the offline server could be "https://key.meteor.com" and the private key wouldn't have to be anywhere but an airgapped machine.
I don't know if there is more of the SSL infrastructure that I'm missing though (I'm not an expert) or if this could practically be reduced down to a tamper-evident one-liner (a la curl https://install.meteor.com | sh). It would be a marked improvement over just passing anything from a potentially compromised server straight to bash though!
> How do you get a code-signing paradigm down to something as simple as curl | sh though? (Well not as simple, but still a human-readable one-liner that works on nearly all Linux systems.)
You don't, really. Not currently anyway. Retrieving a binary/archive and doing out-of-band verification are two logically separate steps.
The problem with your suggestion is that SSL is about transport security. It verifies that you are talking to the right server, but does not provide any guarantees beyond that.
It's not really possible to shoehorn release signing into that, without additional infrastructure.
It doesn't matter how you combine things - the server and the signing system are (and should be!) two separate entities, and you cannot rely on the server to tell you who the signing system is (because that'd give you no better security than not having a signing system at all).
> It would be a marked improvement over just passing anything from a potentially compromised server straight to bash though!
It wouldn't, because as far as I can tell, you're still relying on the server to tell you what the correct release signing key is. How else would you obtain it?
I thought maybe a single-line invocation might piggy-back on SSL as follows:
- get a server's public key that is not online or able to answer requests (because if it were it couldn't be airgapped)
- but still use the key to verify the script that's downloaded from the server that is online.
- only pass the code to sh if it was properly signed by the offline server.
Then the offline server could be "https://key.meteor.com" and the private key wouldn't have to be anywhere but an airgapped machine.
I don't know if there is more of the SSL infrastructure that I'm missing though (I'm not an expert) or if this could practically be reduced down to a tamper-evident one-liner (a la curl https://install.meteor.com | sh). It would be a marked improvement over just passing anything from a potentially compromised server straight to bash though!