From: Hal <hfinney@shell.portal.com>
Date: Tue, 26 Apr 94 08:56:46 PDT
To: cypherpunks@toad.com
Subject: Re: message splitting for better mixing?
Message-ID: <199404261557.IAA02689@jobe.shell.portal.com>
MIME-Version: 1.0
Content-Type: text/plain


Jim Miller
> 
> The idea:
> 
> 1) write sender-side code to split message into N parts and send each  
> part through a different remailer chain.
> 
> 2) decrypt the parts as they arrive as per normal encrypted remailer  
> messages.
> 
> 3) write receiver-side code to detect "a part" and stuff it in a file  
> until the remaining related parts arrive.  When all related parts  
> have arrived, present the complete message to receiver.

Here is a program I found in the usenet archives which will do some of the
splitting and merging features.  Note that the merge is smart in that you
just cat the pieces together and process them.  The main feature of the prog
is that you can reconstruct even with a few missing pieces, necessary because
of the unreliability of remailer email.  I don't think the splitting is
cryptographically strong, but each piece could be separately encrypted if
desired.


> Path: ghost.dsi.unimi.it!rpi!zaphod.mps.ohio-state.edu!cs.utexas.edu!uunet!newsflash.concordia.ca!clyde.concordia.ca!altitude!mirkwood.CAM.ORG!hebrais
> From: hebrais@mirkwood.CAM.ORG (Philippe Hebrais)
> Newsgroups: alt.sources
> Subject: shade -- split a file with shadows
> Message-ID: <hebrais.0xu4@mirkwood.CAM.ORG>
> Date: 13 Dec 92 07:57:05 GMT
> Organization: Secte des adorateurs des semiconducteurs
> Lines: 675
> X-Newsreader: MeNews 2.8.0
> 
> 
>                 SSSSS   HH   HH    AAA    DDDD     EEEEEEE
>                SS   SS  HH   HH   AA AA   DD DD    EE
>               SSS      HH   HH  AA   AA  DD  DD   EE
>                SSS     HH   HH  AA   AA  DD   DD  EE
>                SSS    HHHHHHH  AAAAAAA  DD   DD  EEEE
>                 SSS   HH   HH  AA   AA  DD   DD  EE
>                 SSS  HH   HH  AA   AA  DD  DD   EE
>             SS   SS  HH   HH  AA   AA  DD DD    EE
>             SSSSS   HH   HH  AA   AA  DDDD     EEEEEEE
> 
> `shade' is a file splitting and merging utility.  It takes a large
> file and splits it into uniformly sized blocks.  It can also output
> extra blocks (called shadows).  These shadows can be used to recover
> missing sections if they get corrupted or it they are lost.  With a
> single shadow, `shade' can recover ANY single missing block.  As many
> shadows are needed as there are blocks missing.  If too few blocks
> and shadows are available, nothing can be recovered.
> 
> For example, foo.bar (259042 bytes) is split into 5 sections
> of 45000 bytes, 1 section of 34042 bytes and 2 shadows of
> 45000 bytes.  Each of these 8 parts is sent through email.
> Even if any two of these eight parts gets lost, the original
> foo.bar can be reconstructed.
> 
> `shade' is a simple application of the chinese remainder theorem
> for polynomials with coeficients modulo two.  For more information
> see the comments at the beginning of project.c.
> 
> 
> 
> SAMPLE USAGE
> 
> Split "bar" (111042 bytes) into 20000 byte chunks and output 2
> shadows.  All these parts will be uuencoded and output to
> foo.uu.001, foo.uu.002, etc.
> 
>     % shade -u -k 2 -l 20000 -o foo bar
>     [001] [002] [003] [004] [005] [006] [aaa] [aab] Done.
> 
> Merge these parts back together:
> 
>     % rm foo.uu.003 foo.uu.005
>     % cat foo.uu.* | shade -m -u
>     Merging bar (111042 bytes)
>     Got section 4 (20000 bytes)
>     Got section 1 (20000 bytes)
>     Got section 2 (20000 bytes)
>     Got section 6 (11042 bytes)
>     Got shadow 1 (20000 bytes)
>     Got shadow 2 (20000 bytes)
> 
>     Missing: [003] [005]
> 
>     Recovering 2 sections:
>     [001] [002] [aaa] [004] [aab] [006]
> 
> 
> 
> DISTRIBUTION
> 
> Shade is copyright Philippe Hebrais 1992.  You have the permission
> to use this code is anyway you feel appropriate as long as you give
> credit where it is due.  There is no warranty of any kind.  I am not
> responsible for any damage caused directly or indirectly by this
> program.
> 
> 
> AUTHOR
>           ,
> Philippe Hebrais <hebrais@mirkwood.cam.org>
> 
> --
>       Philippe Hebrais   hebrais@mirkwood.cam.org
>    Voix: (514)731-9146   uunet!philmtl!altitude!mirkwood!hebrais