[ale] little math

[Geoffrey]

Jim Popovitch wrote:
> On Fri, Feb 12, 2010 at 10:26, Geoffrey <lists at serioustechnology.com> wrote:
>> Jim Popovitch wrote:
>>> But the data that is being repeated is itself random.   So you would
>>> essentially be repeating random data sequentially.   The only pattern
>>> is the random data.
>> As I see it, he's creating a single 2 mb random file.  Then write that
>> repeatedly to the disk.  You've just created a pattern.
> 
> If, as I suggested, he did multiple writes in parallel, and then
> destroy the FATs... where's the harm?
> 
>> If you now write encrypted data to that drive, you can easily spot it as the rest
>> of the disk is chunks of 2mb data that are all identical.
> 
> But the new data being written _is_ encrypted, right?  And it will be
> written on top of patterns of random data, right?
> 
> What's specifically wrong with that?

Visually:

random date = 2rtv4

Thus your drive has:

2rtv42rtv42rtv42rtv42rtv4....2rtv4

Now I write some encrypted data:

2rtv42rtv4RANDOMrtv42rtv4....2rtv4


You immediately know where I wrote the data, thus you can exclude a huge 
portion of the drive with your attack.

-- 
Until later, Geoffrey

"I predict future happiness for America if they can prevent
the government from wasting the labors of the people under
the pretense of taking care of them."
- Thomas Jefferson