[rc5] Blocks

wooledge at kellnet.com wooledge at kellnet.com
Thu Oct 9 22:33:57 EDT 1997


Eric Gindrup wrote:

>      It's not clear that the delay will be trivial.  Let's posit a 
>      request-only client that requests 5 blocks per second.  Currently, the 
>      entire effort is completing ~20 blocks per second.  So this client can 
>      tie up 20% of the outstanding keyspace.

One of us misunderstands the key recycling issue; I think it's you.
(At least I hope it's not me. ;-)

When the keys have all been handed out, my understanding is that the
main keyserver will then:

  1) Assemble a new keyspace of all the unchecked blocks (which are all
     "outstanding"); and then

  2) Start handing them out randomly.

The only delay that will be introduced by an "attacker" who requests
large numbers of blocks is the extra burden placed on the key servers.
The clients will still get their keys and/or generate random ones; most
of them probably won't even notice any problem (depending on how long
it takes for the new keyspace to become ready).

>      the malignant 
>      client can (possibly) request the block containing the key (~20%) and 
>      make it appear that no block contains the key (because there are no 
>      blocks that are neither reported nor assigned).  This will necessitate 
>      re-searching the entire keyspace.

This is a different issue.  An attacker who *falsely reports checked
blocks* is very different (and much more serious) than one who simply
fetches blocks and never returns results for them.

Anyone can fetch blocks in large numbers, simply by running the client
in a shell/batch loop.  It doesn't take any hacking skills whatsoever.

Reporting false negative results requires knowledge of the client-server
protocol (not published).  That would require some sort of reverse
engineering, and/or programming skills.

-- 
------------                  Greg Wooledge                  -------------
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