| How about doing this with n of m? Anyone have code? You can also get shade from ftp.dsi.unimi.it:/pub/security/crypt/code/shade.tar.gz 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 -- Adam Shostack adam@bwh.harvard.edu Politics. From the greek "poly," meaning many, and ticks, a small, annoying bloodsucker.