Tuesday, October 5, 2010

Notes from CCS'10

I would like to point out a paper that was presented at CCS'10 today. I liked "Survivable Key Compromise in Software Update Systems" by Samuel, Mathewson, Cappos and Dingledine because it is an excellent example how careful engineering can ease (if not solve) the pains of a worst case scenario. Key compromise, especially of root keys, is the worst case scenarios of any Public Key Infrastructure (PKI) and the PKIs used to authenticate software updates are among those with the highest impact on our entire IT infrastructure. Every software contains some vulnerabilities and without authenticated software updates it is only a matter of time until attackers exploit those vulnerabilities for their purpose. Even worse, a malicious software update could be used to insert new vulnerabilities into secure systems. If you can not trust the PKI and the keys used to authenticate a software update, how can you trust the update? The root keys used to establish a PKI are very well protected and rarely used but, unfortunately, it doesn't mean that they are always secure, it just means that they are less likely to be compromised. But it still happens that you can not trust them anymore, as e.g. https://www.redhat.com/archives/fedora-announce-list/2008-August/msg00012.html shows. Replacing the compromised keys with new, trustworthy ones is a delicate task and regaining the lost trust is difficult. Unfortunately, currently the PKIs used for software updates do not prepare for this case much; therefore the TOR project decided to develop a new PKI system out of existing concepts that is better prepared to cope with this worst case and the result was presented in the paper. I do hope that bigger software projects, such as major linux distributions or Mozilla pick up on this and continue improving the update infrastructure.

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