[Cryptography] grand principles and niggling details

[Tom Mitchell]

On Tue, Dec 20, 2016 at 3:15 PM, John Denker <jsd at av8n.com> wrote:

> On 11/22/2016 01:03 PM, Ron Garret wrote:
>
> > I am constantly surprised by how often discussions of randomness
> > arise on this list, and how long they continue.  Everything that
> > matters about randomness can be summarized in four bullet points
>
> I really don't think so.
>
> Let me offer a different list of grand principles:
>
>   Principle #1:  In the security business, there are very few grand
>    principles.  Mostly what we have is a boatload of niggling details.

.....

>
> > 1.  You need two things: an entropy source, and a whitener.
>
....

>
> I say that is an excellent question,
>

 ....

>
> Here's a particular case:  Consider booting a system, called the
> /target/ system, from a "Live CD" .iso image.
>
.....

>
> 1)  Observe that nobody actually uses CDs for this purpose anymore.
>  For obvious reasons, they use USB flash drives.
>


There are two things missing in a "live: CD or USB-flash boot image.

One is a unique and unpredictable bit pile sufficiently large to support
the generation of communication keys that changes.

A second is the time of day.  A number of IOT devices do not have a
real time clock and tinkering with time has protocol and system issues.

A live CD is a constant -- much like a PRNG in that it will always do what
it does.  It can have unique hard baked secrets or constant hard baked
secrets.
A live USB flash with read write
  -) can be a safe single purpose system.
  -) can install a system.
  -) can repair a system
  -) can infect or disinfect a system.

If I recall SSH and friends expect the time of day on two machines to
be close enough.    I know that system changes and updates can
depend on meta data in  the files system including the various time
stamps.

So add time of day to the list of important volatiles.


-- 
  T o m    M i t c h e l l
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