PSARC/2008/190 - Preinception IPS

[Bart Smaalders]

Garrett D'Amore wrote:
>> Since each action can contain arbitrary attributes, the customer's
>> signature action can contain whatever data he wants; the packaging
>> system happily ignores that which it doesn't know about so he can
>> add new attributes to his signature ad nauseam.
>>
>> This would mean that any actions that are signatures are simply
>> ignored when computing the hash for signing purposes.  Each signature
>> can carry whatever extra data (within reason, of course) is deemed
>> necessary by the signer.
>>
>> If the customer is worried about retrieving these packages from a repo
>> run by a hostile which is attempting to edit his meta data, we can 
>> always include just the signature being generated (minus the hash value)
>> in the hash.
>>
>> Thus, each signature stands alone, but if present cannot be altered w/o
>> detection.
> 
> I think you want the hash value in the signed portion.  Otherwise, how 
> do you keep someone from reattaching a different signed meta data from a 
> "bad" package to a "good" package?
> 
> Possibly all you need is just the hash signature.
> 
> I still don't really understand whether meta data can alter the behavior 
> of the software (either the installed software or the installation 
> software itself) -- can it?
> 
>    - Garrett

The signed portion of the manifest would consist of all the entries in 
the manifest (actions) aside from signatures, _plus_ any metadata 
included in the signature being generated.

Thus signatures cannot be spoofed or exchanged, but they may generated 
by anyone w/ a key and added to the manifest.  They cannot be altered
w/o invalidating that signature.  The rest of the manifest cannot be
altered either w/o invalidating all signatures.

For example, suppose the manifest consists of:

set name=fmri value=pkg:/cheeseshop at 1.0
dir group=sys mode=0755 owner=root path=/scripts
file b0b7615454f3a3ec0d0d159677618bbb476052e0 group=bin mode=0444 
owner=root path=scripts/cheeseshop.txt
signature ....

and you wish to sign it again with the additional meta data of
airspeed_of_unladen_swallow=20

then the complete hashed text would include the manifest text
minus the already present signature but including the 
airspeed_of_unladen_swallow=20 in a canonical format.

- Bart



-- 
Bart Smaalders			Solaris Kernel Performance
barts at cyber.eng.sun.com		http://blogs.sun.com/barts
"You will contribute more with mercurial than with thunderbird."