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Closing the window of attackClosing the window of attackPosted Aug 29, 2008 1:37 UTC (Fri) by tialaramex (subscriber, #21167)In reply to: The proposed Fedora key-migration plan by pragmatine Parent article: The proposed Fedora key-migration plan
I don't agree. The factor you're missing is /time/ which is often the most critical factor in design of cryptographic systems.
Often an attacker can eventually obtain a secret (e.g. crack the Fedora signing key's passphrase), but they obtain it too late to be useful and the cryptosystem has functioned as desired. Nobody in the business of keeping serious secrets expects them to last forever, but they only have to last long enough. On June 5th 1944 the detailed plans for the Normandy landings were among the most important secrets in the world. Over the following days and weeks they became merely a historical curiosity.
Updating everyone to new keys closes the window of attack, giving the attackers much less time to capitalise effectively if they do in fact have, for example, an encrypted signing key for which they are trying to guess the passphrase. It's the same reason it makes sense to occasionally change your password. If someone has been slowly trying to figure out the password by watching you type it in, or they have been trying to break the PHK MD5 hash they managed to steal from an old backup, all their slow work is undone by simply changing the password, and they must begin again.
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Closing the window of attack Posted Aug 29, 2008 9:14 UTC (Fri) by pragmatine (guest, #39557) [Link]
that assumes the passphrase of the old key hasn't already been cracked though. if it has all bets are off.
Closing the window of attack Posted Aug 29, 2008 23:10 UTC (Fri) by Sutoka (guest, #43890) [Link]
For an administrator, if the password of the key has already been cracked then you should try to verify the new key from as many different sources as possible first.
It's also possible the key *wasn't* stolen, and that this is just a precautionary measure to make sure the packages signed by the attacker don't get installed on the user's system as if they were valid.
I wonder if there's a version of the fedora-release package signed with the new key, allowing the admin to first install the key manually then use the newer version of the RPM (thus not having to trust the old key at all).
In the future, Fedora might wanna have multiple keys. One *normal* key they do all their signing with (like now), then another emergency key in case, well, this happens. The emergency key's only purpose would be to make it easier to replace the standard key (i.e. this fedora-release package would be signed with the emergency key). Obviously Fedora would want to make sure the key was encrypted and not stored somewhere that it'd be inconvenient to get to (preferably not accessible by a computer).
Closing the window of attack Posted Aug 30, 2008 0:02 UTC (Sat) by bojan (subscriber, #14302) [Link]
> In the future, Fedora might wanna have multiple keys.
If Fedora packages were signed by multiple independent signatories, yum could be designed to accept (for instance) only packages signed like this:
- Fedora key
or
- 5 keys from independent signatories
In that case, a compromise of a single key would be easily avoided, as long as you had enough signatories in the pool to make up the numbers (and with vast number of people involved in Fedora, this is definitely possible).
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