Re: [dtn-interest] Comments on RFC 5050

[Amy Alford <[e-mail]>]

If you replaced PIB with BAB in your scenario, authentication would fail.
 However, this could only occur if node C is non-security aware.

Dictionary entries in extension blocks aren't protected by PIB or PCB.  An
ESB ciphersuite that provided integrity would protect any extension block
it was applied to.  There isn't a PIB equivalent for extension blocks (if
there were, it would be what you would use to protect dictionary entries
for an extension block (as well as the block contents)).  A revision to
6257 will probably provide a PIB equivalent for extension blocks.



On Mon, Jun 24, 2013 at 3:03 PM, Michael Noisternig <
[e-mail]> wrote:

> Am 24.06.2013 20:48, schrieb Amy Alford:
>
>
>>         4.7. Dictionary Revision:
>>         "Any [unreferenced] strings (scheme names and SSPs) in a bundle's
>>         dictionary ... may be removed from the
>>               dictionary at the time the bundle is forwarded."
>>         ...subject to that authenticity is not lost.
>>
>>            * Yes, but that’s implicit.  Strings that are needed in order
>> to
>>
>>              verify authenticity are referenced, so they can’t be
>>         removed from
>>              the dictionary.
>>
>>
>>     Could it happen that some extension block be processed, removed and
>>     its EID references removed by some intermediate node on a security
>>     path? I am still trying to figure out what is possible with the
>>     current security spec.
>>
>> Yes.  Talking through a specific example is probably the best way to
>> clarify this.  Suppose we have a very boring network of:
>>
>> Node A --- Node B --- Node C --- Node D
>>
>> Node A sends a bundle to node D, with a PIB block with security source
>> of node A and security destination of node D.  Node B can add a PIB
>> block with security source node B and security destination node C.  When
>> node C removes the PIB block destined for node C, it may change the
>> dictionary.  But, it would change it back to its state at the time the
>> first PIB was calculated.
>>
>> In any event, PIBs don't cover the dictionary (only the specific entries
>> being used in the blocks covered by the PIB).  BABs cover the
>> dictionary, but are always the last security block added and first
>> removed.  The only time dictionary changes would invalidate a BAB are if
>> the dictionary was modified at a non security aware node.  However, if
>> the dictionary was being modified because of a change to an extension
>> block, that would invalidate the BAB anyway.  The only dictionary
>> changes that would invalidate a PIB are gratuitous changes to case
>> insensitive fields.
>>
>> - Amy
>>
>
> Ah, I missed that the PIB does not protect the complete dictionary.
> Otherwise, I was more thinking about partially overlapping paths. Something
> like where Node A adds some (non-security) extension block together with
> some new dictionary entry, both to be processed and removed by Node C,
> whereas Node B adds a PIB to be consumed by Node D.
>
> But what about dictionary entries by non-primary blocks? How are they
> being protected end-to-end?
>
> Michael
>
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