[svn-inject] Tagging upstream source version of scowl

[deb_pkgs/scowl.git] / 6 / r / enable / CHECKSUM.DOC

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+                        THE "CHECKSUM" PROGRAM\r
+ÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜ\r
+\r
+A "checksum" is a uniquely generated file signature, a sort of digital\r
+certificate of authenticity for that file. It is a number calculated\r
+from the very contents of the file. Changing a single character in the\r
+file results in a different checksum. This makes it easy to determine\r
+whether a file has been tampered with or altered.\r
+\r
+A generic checksum utility might work by assigning each character (letter)\r
+in the tested file a numerical value according to its relative position in\r
+the alphabet. If we were to give 'a' a value of 1, then 'b' would be 2,\r
+'c' would be 3... and finally 'z' would become 26. Finding the sum of\r
+all the numbers associated with the characters in a word file would\r
+yield a ridiculously large number, so, at periodic intervals, one could\r
+divide the running total by a cleverly chosen "magic number" and only\r
+keep the remainder. Throw in an additional factor to distinguish adjacent\r
+characters from one another, so that a transposition of letters makes a\r
+difference in the final total. To increase security, output the checksum\r
+in hexadecimal, or base 16 notation, so that the letters 'a' through\r
+'f' stand for the decimal numbers 10 through 15.  Simple, yet effective.\r
+\r
+For all you technical types, this is nothing more than a simple "hashing"\r
+algorithm, nevertheless, it serves its purpose by detecting most instances\r
+of tampering and alteration in files\r
+\r
+The first release of ENABLE used a checksum utility written by one\r
+of the maintainers of that list. That particular checksum program\r
+had a clever hack to return the same checksum for both the DOS and\r
+UNIX versions of an otherwise identical list. In the interests of\r
+increased security, the original checksum program will no longer be\r
+distributed with ENABLE. Users of the ENABLE list wishing to verify\r
+that their copy of the list is pristine are now urged to download the\r
+"MD5 Command Line Message Digest Utility", written by Ron Rivest\r
+(of RSA fame) from http://www.fourmilab.ch/md5/. The "md5.zip"\r
+file from that site contains both a 32-bit Windows binary and the\r
+source code for a UNIX build. The md5 signature for the WORD.LST\r
+file in ENABLE2K is B175518814B6B8787CFE34C7BB8705B6 (if the file is\r
+converted to UNIX format, with the CR's removed, the md5 signature is\r
+E942E9E884090D2BDB02265864882231).  The maintainers of the ENABLE list\r
+regret that they can offer no assistance in using "md5".\r
+\r
+Those interesting in delving more deeply into the subject of file security\r
+may obtain Phil Zimmerman's "PGP" program. It is considerably more secure,\r
+if more complex, than even the excellent md5 package. The excellent book,\r
+PGP: PRETTY GOOD PRIVACY, by Simon Garfinkel (O'Reilly & Associates,\r
+Inc., ISBN 1-56592-098-8), gives in depth coverage on the subject.\r
+\r
+\r
+                                 M\Cooper\r
+                                PO Box 237\r
+                       St. David, AZ  85630-0237\r
+                        thegrendel@theriver.com\r
+               http://personal.riverusers.com/~thegrendel/\r