Re: Thinking aloud.

On 25 Oct 2012, Nigel Cunningham uttered the following:

> Thanks for your response - I'm no cryptography guru, so it's good to
> hear from people who obviously know more than I do. I guess the way to
> go then is to build a table of hashes that have been seen and compare
> the actual content if/when you get a collision? I suppose that would
> also help in seeing whether/how often pages have the same content.

You'd want a debugging option to do that, because reading the old page
in to compare it is going to be every bit as expensive as writing the
new one out would have been.

> Also, may I ask?: How does checksumming a page compare to using SHA1
> hashes for git blobs?

Pretty much the same.

>                       I've read that Linus isn't concerned about
> collisions there, but don't fully understand why it's not an issue
> there, but is here.

Well, it's not an issue there because it's insanely improbable that it
would happen by chance, and git hashes are not meant as a security
feature. It's possibly an issue here because it is quite possible for
e.g. cryptanalysts to be using Linux and have a page of memory filled
with something which they *know* will cause a hash collision because
they've just been studying it!

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NULL && (void)