Razor2 supports nilsimsa "fuzzy" hashes, but right now those are disabled server-side because of bugs in the hash algorithm resulting in a high collision rate.
Thus ephemeral sigs are what razor2 uses, for now. It is defeatable, but it does require the spammer to change a lot of bytes scattered around across the whole message. Since the hashed selection is chosen at random and changes every so ofteh (the razor server stores the whole message body of reported spams to facilitate such changes), the spammer never knows where to insert his "razor compensation" garbage bytes.. so he has to insert them all over the place.
It's defeatable, but requires some effort on the pat of the spammer, which is at least something. It's definitely a lot better than razor1 which just SHA hashed the whole body, allowing spammers to compensate by changing any one byte of the body.
You can read a little about the ephemeral signatures algorithm on the razor site:
http://razor.sourceforge.net/docs/whatsnew.html
At 02:59 PM 12/13/2002 +0000, Justin Mason wrote:
> Razor2 uses ephemeral sigs by default, which only hashes some subset of > the body of the email. ie: bytes 50-200, then later it might be > 120-900.Well, I hope that's not it -- that's pretty trivial to work around too ;) --j.
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