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If CAs don't have private keys , how are they signing certificates?
by jiggy2011 13y ago
If CAs don't have private keys , how are they signing certificates?
- blibble 13y agoyou transmit your public key, identity and server information. the CA then verifies your identity, and then produces a certificate by signing (using their private key) the message digest of the concatenation of: - certificate information: server name/organisation/country/... (the "subject"), start date, end date, etc - your public key - the subject of their certificate your private key should never leave your system.
- jiggy2011 13y agoRight, but the CA in that scenario has their own private key. If the private key for say Verisign was shared with the NSA, then the NSA would be able to MITM anybody using a cert that appeared to come from verisgn.
- blibble 13y agothey wouldn't share their key, the complicit CA would generate a certificate for a key generated by the NSA with the CA capability bit enabled. the NSA could then can use that to MITM sites without explicit pinning.
- jiggy2011 13y agoIf they NSA could coerce a CA into sharing the key, they could make less detectable MITM attacks. So when you look at the chain you see: Verisign (lol j/k really the NSA) -> Site cert Rather than: Verisign -> Third party CA (suspicious) -> Site cert If you pinned the site certs you should be able to defeat both of these.
- 23david 13y agowhy couldn't they coerce all CA's into sharing the keys?
- antocv 13y agoThey can and they most probably have done that. Even Iran and China did it, stole root CA private keys, kind of sloppy because we know. Coercion by legal means, moles or good old hacking or planting bugged hardware in the targets system and extracting private keys. Its within the realms of NSA, remember, they have the capability to make their own processors.
- nivla 13y agoThe CA doesn't have/or need your private key. It works by signing your public key with its private key, thus affirming that you are whom you say you are. Think of it as getting a recommendation letter from your professor with his signature. Public and Private keys are also cryptographically related to each other, so a change in one will affect the other.
- jiggy2011 13y agoI mean , they do have their own private keys. So anyone with access to a CA's private key can pretend that they are that CA.
- marcosdumay 13y agoYes, but they can't pretend that they are the company you are talking to... Or at least they'll leak enough information to get caught if they do that in a massive way.
- jiggy2011 13y agoThey can if they simply sign a cert that is identical in all but public key.