[OLPC Security] Securing the laptop: First pass for some basics.

[Christopher Blizzard]

Tim Flavin wrote:
>>
>> > Instead of generating
>> > cryptographic checksums from the files on the laptop,
>> > the checksums would be contained in files cryptographically
>> > signed by the school districts and schools.
>>
>> Linux packaging generally has check sums files in packages that allow
>> you to do verification, and digital signatures on the packages
>> themselves.
> 
> The problem with packages is that you have to check the signiture on
> each one of hundreds if not thousands of packages before you can trust
> the checksums. Verifing signatures is compute and in our case power
> intensive.

We could make this a lot faster.  The reason why we end up checksumming 
every file in every package is because every package is separate and 
it's nice to be able to tell users what file has been changed.  But 
those aren't necessarily our goals.

What you could do is have a manifest of files and run a single md5sum on 
that set based on a well-known algorithm to get the files in the right 
order.  That way you can tell that something has gone wrong in a 
particular set, and you can probably use that information to track down 
which files has changed using an offline database.

> This program would run in several modes.  The beginner could use it to fix
> problems get his laptop back in working order.  This would be the
> equivalent of a
> partial reload.  For more advanced students, it can flag the files and let
> them decide what to do.
> 
> My basic aim is to be able to quickly see if the system is OK and give a
> "FIX IT" button to inexperienced user.  (We may have a lot of them soon.)
> 

Like a big "Undo" button? :)

I would love this as well.  What do you use for a source?  Another 
laptop?  Some server?  (Which won't always be there?)

> Good point.  I was hopeing that there would not be a lot of configuration
> files. Hostname and password files would be special cases. Most of the 
> other
> files I can think of are .profile type files in /home/*.  We can back these
> up and replace them with working default files and let the student
> replace them with the backups. This program is mostly intended to help
> people who don't edit a lot of files in /etc.

My personal goal is to take the system files from one machine and clone 
them to another and have them "just work."  This means that config files 
really do need to be transitory.  That is, you never have to change a 
system config file in order to do something to your system.

--Chris