[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

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

Step 1: Rename your buff-in.rc5 file to something else (I use
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

Colin L. Hildinger
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