Full Disclosure mailing list archives
Re: Expired certificate
From: Pavel Kankovsky <peak () argo troja mff cuni cz>
Date: Sun, 25 Jul 2010 00:39:13 +0200 (CEST)
On Tue, 20 Jul 2010, Marsh Ray wrote:
The usual logic given for this and other types of mandatory password expiration schemes is that it limits the time of exposure when the credentials are compromised. These days this reasoning makes less sense when the attacker might only need to use his unauthorized access for 50ms or so to install a persistent backdoor.
There are still other risks. Old copies of keys (or passwords) can be disclosed accidently or during an attack. (With the recent explosive growth of storage capacity it is a little bit too easy to keep many old forgotten copies of sensitive files.) Advances in cryptology and computing power can make old keys unsafe. People may neglect to revoke certificates that have become invalid (e.g. a personal certificate for someone who has deceased). And of course the risk of private key being stolen and being abused even after the compromised system has been cleaned up. There are situations where it is not possible to assume the other party is able to keep an up to date copy of CRL and check it (moreover, the lack of expiration date would make CRLs grow beyond any limit).
Drivers licenses, (as Pavel said) passports, most kinds of real-world credentials expire. In the computer field we deal with 10+ orders of magnitude on the time axis (10 years vs 100 ms) so normal policies don't scale well.
Even in the realm of passports et al. 10 years is way too long to prevent abuse. But it helps to reduce the number of documents that might be accepted as valid despite having been lost or stolen, carrying photographs too old to allow reliable verification or containing information that is not valid any longer. The problem is a conflict between security and convenience. Ironically, online communication allows a rather elegant solution: you can have a hierarchy of certificates starting with short-lived certs for routine operation issued online by the lowest level of intermediate CAs with each level offering less automation to reduce exposure and longer lifetimes to make up for lost convenience. Unfortunately, this approach (while being quite feasible from the technical POV) appears to be incompatible with the business model of existing CAs. On Thu, 22 Jul 2010, Dan Kaminsky wrote:
Suppose I have five hundred web servers with five hundred expiration dates, strewn out roughly uniformly over a three year period. That means, I have about one expiration every two days. Now, to run a change: [...] Lets say this is 8 man hours. That means this is 4,000 man hours of work. Assume the employee doing this work has an average cost to the company of $60/hr (remember, you need to roughly double the cost of a full time employee, after you factor in benefits, payroll taxes, etc).
If you have got 500 servers that need renewed certificates then you have got 500 server that need patches installed, not to mention other routine admin tasks. If you need 8 man hours per server to renew one certificate, how many man hours per server do you need to deploy one patch? On Fri, 23 Jul 2010, Meadow wrote:
If your organization really did have the expiration staggered at every 2 days, then you should take a bunch of servers (grouped by segment/application/whatever makes sense in your environment) and renew all the certs on that group of servers at once, even if they aren't all quite expired yet. You should also fire your program manager. The savings in labor and down-time would make up for the one-time cost of renewing some certs prematurely.
Many (if not most) CAs let you renew a certificate two or three months before its expiration and give you the remaining time back. One who needs to renew one certificate every other day can do it once in 2 or 3 months in batches of up to 30 or 45 renewals without losing anything. -- Pavel Kankovsky aka Peak / Jeremiah 9:21 \ "For death is come up into our MS Windows(tm)..." \ 21st century edition / _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.grok.org.uk/full-disclosure-charter.html Hosted and sponsored by Secunia - http://secunia.com/
Current thread:
- Re: Expired certificate, (continued)
- Re: Expired certificate Dan Kaminsky (Jul 17)
- Re: Expired certificate Pavel Kankovsky (Jul 18)
- Re: Expired certificate Marsh Ray (Jul 20)
- Re: Expired certificate Dan Kaminsky (Jul 22)
- Re: Expired certificate Marsh Ray (Jul 22)
- Re: Expired certificate Dan Kaminsky (Jul 22)
- Re: Expired certificate Marsh Ray (Jul 22)
- Re: Expired certificate bk (Jul 23)
- Re: Expired certificate Meadow (Jul 23)
- Re: Expired certificate Marsh Ray (Jul 24)
- Re: Expired certificate Pavel Kankovsky (Jul 24)
- Re: Expired certificate Dan Kaminsky (Jul 24)
- Re: Expired certificate Dan Kaminsky (Jul 24)
- Re: Expired certificate Pavel Kankovsky (Jul 25)
- Re: Expired certificate Dan Kaminsky (Jul 25)
- Re: Expired certificate Marsh Ray (Jul 26)