[Http-crcsync] General comments on crcsync document

Patrick McManus mcmanus at ducksong.com
Fri Jul 17 13:32:19 EDT 2009


you've triggered an a-ha in me.

for some reason in my head I had the server calculating the same number
of hashes as the client (e.g. 40).. but that's not true.. the server
does a rolling calculation and, in the case of all misses calculates
every possible window - which in the case of a 100K document is just shy
of 100K different hash values.. which is a lot more than 40 ;)

do I have that right?

so 100k crcs each of which could falsely match 40 different client
supplied crcs gives us 4 million lottery tickets into a 4.2 billion
address space.. so that puts us on the same page at 1 in 1000 (modulo
those bogus assumptions).

That's a whole lot of crcs ;)







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