🚀 go-pugleaf

uri@watson.ibm.com (Uri Blumenthal) writes:

>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].

    Tripwire supports hooks for up to ten signature routines.  We
ship it with MD5, Snefru, CRC32, CRC16, MD4, and MD2.  Although
the CRC routines are not "signatures" in the cryptographic sense,
they are nice to have since they are considerably faster than the
more secure algorithms -- which are (hopefully) one-way hash
functions.

    By default, Tripwire checks a file's MD5 and Snefru signature.
However, any combination of signature checks may be used to fit
your system's performance vs. security equation.  e.g., checking
MD5 signatures once per day, but checking CRC32 once every hour
is possible using Tripwire.

    Furthermore, if you have the newest and most secure signature
algorithm, say the super-secret Gurgleblatz Mark VIbis XIX routine,
you can simply add an interface to it to Tripwire's arsenal.  The
interface is simple enough:

	    int signature_routine(int fd, char *sig, int siglen);

    (Tripwire stores an array of pointers to the signature functions,
so it's very general.  Just compile it right in!)

>	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...

    Tripwire includes a 'sigfetch' utility that simply spits out the
signature for a given file.  A simple shell script could offer this
functionality.  As part of the Tripwire design, we require that the
database be immediately moved to a safe location (e.g., some read-only
media).

    In fact, I'll make sure a shell-script wrapper to do this is
included in the next Tripwire release.

Gene