3.10.pki - CS 161 Computer Security Spring 2010...

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Unformatted text preview: CS 161 Computer Security Spring 2010 Paxson/Wagner Notes 3/10 More on Key Management These notes go into a little more detail on Public Key Infrastructure (PKI) and other approaches to key management that we didnt have time to cover in the previous lecture. 1 Certificate Chains and Hierarchical PKI Last lecture, I mentioned as an example that Arnold Schwarzenegger could sign a certificate attesting to the public key of each California state employee. However, in practice that may not be realistic. There are over 200,000 California state employees, and Arnold couldnt possibly know every one of them personally. Even if Arnold spent all day signing certificates, he still wouldnt be able to keep uplet alone serve as governor. A more scalable approach is to establish a hierarchy of responsibility. Arnold might issue certificates to the heads of each of the major state agencies. For instance, Arnold might issue a certificate for the University of California, delegating to UC President Mark Yudof the responsibility and authority to issue certificates to UC employees. Yudof might sign certificates for all UC employees. We get: { The University of Californias public key is K Yudof } K- 1 Arnold , { David Wagners public key is K daw } K- 1 Yudof This is a simple example of a certificate chain : a sequence of certificates, each of which authenticates the public key of the party who has signed the next certificate in the chain. Of course, it might not be realistic for President Yudof to personally sign the certificates of all UC employees. We can imagine more elaborate and scalable scenarios. Arnold might issue a certificate for UC to Mark Yudof; Yudof might issue a certificate for UC Berkeley to UCB Chancellor Robert Birgeneau; Birgeneau might issue a certificate for the UCB EECS department to EECS Chair Stuart Russell; and Russell might issue each EECS professor a certificate that attests to their name, public key, and status as a state employee. This would lead to a certificate chain of length 4. In the latter example, Arnold acts as a Certificate Authority (CA) who is the authoritative source of in- formation about the public key of each state agency; Yudof serves as a CA who manages the association between UC campuses and public keys; Birgeneau serves as a CA who is authoritative regarding the public key of each UCB department; and so on. Put another way, Arnold delegates the power to issue certificates for UC employees to Yudof; Yudof further sub-delegates this power, authorizing Birgeneau to control the association between UCB employees and their public keys; and so on. In general, the hierarchy forms a tree. The depth can be arbitrary, and thus certificate chains may be of any length. The CA hierarchy often is chosen to reflect organizational structures....
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This note was uploaded on 04/14/2010 for the course CS 161 taught by Professor Staff during the Spring '08 term at University of California, Berkeley.

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3.10.pki - CS 161 Computer Security Spring 2010...

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