At 9:17 AM 7/6/96, Declan McCullagh wrote:

"We are writers, not crytographers."

-Declan .... This seems to be an application for Bloom filters. See page bottom of page 561 in Knuth's "Searching and Sorting", First Edition. (Vol 3 of Art of Computer Programming)

With a Bloom filter you can hide which URLs you reject yet quickly rejecting particular URLs. Compute SHA(URL) yielding 160 bits. Divide that into 16 ten bit quantities b[i], for 0<=i< 10. Reject the access if P[b[i]] = 1 for each i. P is an array of 1024 bits computed by someone with the index prohibitorum. (pardon my Latin) Yes, this excludes 1/1024 "falsely accused" URLs, but you get the idea.