[RC5] DES 2 (in preparation of)

Colin L. Hildinger colin at ionet.net
Wed Jan 7 23:59:48 EST 1998


On Wed, 7 Jan 1998 14:01:49 -0800 (PST), Mary Conner wrote:

>
>Okay, here's the scenario.  We'll assume the one we were originally
>talking about, an 80 block in-buffer, the client does 30 blocks a
>day, they are faithfully flushed once a day, either by hand, or by
>having a 30 block out-buffer.  The keyspace is exhausted, the blocks
>are reissued, and those 50 stale blocks are done by someone else.
>But then either the computer's owner goes on vacation, or there is
>some network problem, and the client goes on with doing those 50 blocks
>which have already been done by someone else.  Better to be doing random
>blocks than 50 that have already been done.  I don't expect this to be too
>big a deal with DES II, but I've heard that with rc5/64, when the 0x64
>keyspace is exhausted, once return of 0x64 blocks trickles off, those
>that have not been returned will be reissued in order to close out the
>keyspace.

Well, the keyspace is so large that by the time they start
redistributing the 0x64 blocks the number that will be out there will
be very tiny to say the least.  I mean, it's almost all distributed now
I'd wager, but how long before they start re-sending?  They might as
well keep distributing only new keyblocks until they've all been
distributed once.  At that point the 0x64 ones would have been
distributed years in the past.

>In order to avoid this situation you can do one of three things.
>1) don't run with a in-buffer bigger than your out-buffer, and don't
>manually flush the client on a regular basis.
>2) if you do decide you want to do this, then when you start seeing
>keyblocks from outside the current subspace let your in-buffer go empty to
>clean out those blocks.
>3) or, once you start seeing keyblocks from outside the current subspace,
>you can delete your in-buffer to ensure that your "dead space" will
>not have blocks that will eventually be reissued before you're likely
>to get to them.
4) And (IMO a really good option is) every once in a while do the
following:

Step 1: Rename your buff-in.rc5 file to something else (I use
buff-bak.rc5)
Step 2: Start a second instance of the client some time when you're
going away for a long period.  Use the "-in buff-bak.rc5 -runbuffers"
options and said instance will use the buff-bak file and exit when it
finishes the buff-bak.rc5 file.

When you get back from your trip the "primary" client will be happily
working and the one using buff-bak.rc5 will have cleaned it up for you.
 Problem solved.  As a matter of fact you could even write a script and
schedule it to do this once a month or something if you're really
worried.



Colin L. Hildinger
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