Random Number Seed in File? (was: ElcomSoft Co.Ltd. fould a flaw in V3Beta1)

On Fri, 24 Mar 2006 01:31:08 -0500, Rony Shapiro <[email protected]> wrote:
>
> The good folks at ElcomSoft have found a weakness in the new release that
> makes the master encryption key vulnerable to a brute-force attack when
> running pwsafe on pre-XP versions of Windows, basically since we  
> fallback to
> the rand() prng for those platforms.
>

I was thinking about this the other day. So all implementations of Password
Safe require a good random number generator (whether provided by the  
operating
system or not), and, just as important, need to seed any PRNG. It is not  
easy
to come up with a good source of entropy to initialize the PRNG's seed.  
Password
Gorilla currently uses the (microsecond) timing between keystrokes when  
the user
enters the master password.

I was wondering if it would be a good idea to set aside a header field in  
the
V3 database format for the seed, so that it can be carried over across  
runs.
This new header field would be a random number that an implementation could
optionally use to (help) seed a PRNG.

When a database file is opened, the implementation would add some "new"  
entropy
to the one in the header field, and, if the file is saved, update the seed  
with
new random numbers. The entropy in the file would then "get better" over  
time,
as more and more fresh randomness is added to the initial value from file
creation.

If an implementation used an external (e.g., OS-provided) (P)RNG, it could
ignore the header field, but would still have to fill in the random number  
when
saving the database.

IIRC, Linux does something quite similar for its /dev/random entropy  
generator.

This field would have to be encrypted, a la the B1-B4 header fields.

Does this make sense?
Frank


-- 
Frank Pilhofer, [email protected]


-------------------------------------------------------
This SF.Net email is sponsored by xPML, a groundbreaking scripting language
that extends applications into web and mobile media. Attend the live webcast
and join the prime developer group breaking into this new coding territory!
http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642