🚀 go-pugleaf

|> >If I can make that backward calculation either
|> >directly or by trial-and-error in a reasonable time, then your
|> >signature protection system is no protection.
|> 
|> I strongly agree. That's why I wrote my ATP program. A version
|> portable to BSD will be ready soon. Anyway ATP is very like tripwire
|> but is protects its database with DES/CBC. I gonna release it to
|> the net and to ftp@ghost.dsi.unimi.it:/pub/security as soon as I finish.

I'd say two things:

	a) The signature should be cryptographically strong.   It
	   means that it's infeasible for an adversary to compose
	   a message with the same signature as yours.  There are
	   several algorithms available, MD5 one of them... There
	   is no reason to be afraid of an adversary  being  able 
	   to "make backward calculation" [using decent sig, that 
	   is].

	b) The database of signatures is to be protected from [malicious] 
	   modifications [because since the algorithm is known, an enemy,
	   even if he can't modify your file  to fit the "old" signature,
	   could in this case to change the file AND the signature]. I'd
	   think, DES/CBC is quite enough of protection...
-- 
Regards,
Uri.		uri@watson.ibm.com
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