y even if someone obtains access to that session-state memory, the illicitly retrieved session-state data are meaningless. The price for such an elevated degree of protection is a significant decrease in crypto- graphic throughput performance as the security coprocessor now has to meticulously encrypt and decrypt all the session's cryptographic metadata-that is, the data that it needs in order to actually encrypt and decrypt user traffic on behalf of the network processor or host CPU. Be extremely cautious with public-key cryptographic performance ratings, as companies unfortu- nately report results partially and in arbitrary units that are extremely difficult to compare. The prospective user should therefore understand the constraints of the technology and ask vendors the appropriate questions until the full picture is disclosed. IPsec Acceleration Some manufacturers quote RSA operations or DH operations, but in addition to being vague, they are not even close to defining what is actually obtained by acquiring their prod- uct. IPsec has multiple parameters that can define the computational context. It is therefore important to know what parameter compares with what. It is important first and foremost to know the follow- ing items as an IPsec accelerator spends most of its time encrypting and reformatting payloads of packets: How it performs with a typical (such as RC4) and worst-case cipher (such as the combination of Triple DES with SHA-1 hashing). How it performs with different key sizes (and, when applicable, when combined with different block sizes). Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. SECURITY COPROCESSORS SECURITY COPROCESSORS 393 How performance is affected when IPsec is configured respectively with AH, ESP, and potentially AH/ESP protocols. What happens when IPsec works in transport and, more importantly (in terms of wor