Web Caching

Content Integrity

Can you trust the information you receive from a cache? How do you know it has not been modified? How do you know it is what the origin server intends for you to see?

This is an extremely difficult problem, with no known solutions at this time. TCP does not currently provide any form of end-to-end security, which means this problem is not specific to HTTP or the Web. The Transport Layer Security protocol (TLS, formerly Secure Sockets Layer) does provide end-to-end security on top of the network transport protocols. TLS protocols [Dierks And Allen, 1999] are designed to prevent eavesdropping, tampering, and message forgery. However, the security provided by TLS is in effect only for the duration of the data transfer. It does not guarantee—especially for cache hits—that the object you receive has not been modified since the origin server generated it. Unfortunately, we do not have a general purpose digital signature scheme for web objects. Even if such a thing did exist, to be of any real value it would require out-of-band communication for the key exchange. In other words, it would be pointless to retrieve signing keys from the cache.

Recent security features being added to DNS [Eastlake, 1999] might be able to support a scheme for authenticating web objects. For example, lets say you request the URL http://www.monkeybrains.net/index.html. The response is an HTML page that includes, in comments, a digital signature. To validate the signature, you need the public ...