[Full-disclosure] Re: SecureW2 TLS security problem

[Valdis.Kletnieks at vt.edu]

On Tue, 04 Oct 2005 15:08:40 +0200, Simon Josefsson said:

>    • The process ID of the current process requesting random data
>    • The thread ID of the current thread within the process requesting random 
data
>    • A 32bit tick count since the system boot
>    • The current local date and time
>    • The current system time of day information consisting of the boot time, c
urrent time, time zone
> ...
> plus many more sources.
> 
> I wonder if anybody has quantified the amount of entropy that could
> realistically be extracted from the mentioned sources.

Umm.. "not much". ;)

For instance, note that there's "32 bit tick count" and "current time".  Wandering
over to Netcraft will give you the uptime - and how many times do they fold
"current time" in there? Each additional one adds exactly zero entropy.  Similarly,
you get 4.5 bits of entropy *MAX* from 'time zone' - and if you can guess where
the box is down to the continent, you're down to 2-3 tops, and possibly exactly 0
if you know the city....

Similarly, if "process ID" and "thread ID" are sequentially allocated integers,
there's probably only 3-4 bits of entropy in the process ID (since at each reboot,
everything starts in the same order each time)
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