Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site burl.UUCP
Path: utzoo!linus!philabs!cmcl2!floyd!clyde!burl!rcj
From: rcj@burl.UUCP (R. Curtis Jackson)
Newsgroups: net.puzzle
Subject: Re: three spies
Message-ID: <352@burl.UUCP>
Date: Wed, 19-Oct-83 11:05:44 EDT
Article-I.D.: burl.352
Posted: Wed Oct 19 11:05:44 1983
Date-Received: Thu, 20-Oct-83 07:56:23 EDT
References: <534@ihuxw.UUCP>
Organization: Western Electric, Burlington, NC
Lines: 66

I have had three people ask me what rot 13 is, so I decided
to (once again, for you net.jokes readers) explain:

rot 13 is a method of encryption that is used to hide things from
those who might not want to see them.  Offensive jokes on the net
are encrypted in this manner so that only those who want to read
them have to do so.  It is accomplished by adding 13 to the ascii
value of each letter; this addition of 13 is wrapped around within
each of the two (upper and lower case) character sets.  For instance,

'c' + 13 ==> d e f g h i j k l m n o = 'p'
'T' + 13 ==> U V W X Y Z A B C D E F = 'G'
etc.

Here is a program that reads stdin and outputs stdout; it will encrypt/
decrypt any rot13 text.  Because it is a filter, it can easily be used
at the '?' prompt of readnews with the 's' option:

? s | rot13

It will take an argument for the rotation value -- but the default (and
the standard for netnews, because it is easily reversible) is 13.

NOTE:  IF YOU ARE RUNNING ONE OF THE NEWER VERSIONS OF NEWS (I BELIEVE
IT IS 2.10 AND UP), YOU CAN TYPE AN UPPER-CASE D ('D') TO THE '?' PROMPT
OF READNEWS, AND IT WILL DECRYPT ONLY WHAT IS ENCRYPTED WITH ROT 13
AUTOMAGICALLY.  It does not always work correctly, though; so you may
have to back up with a '-' ('D' option does not accept a '-' modifier
like 'f' and 'r' and 's'), then type 'D 13' to the prompt and it will
perform the same function as the program below.  Note that the 'D'
option is NOT like the 's' option; you can save an article with 'D', but
you lose the header and the only way to do it is 'D > filename'.
====================================================================
/* program to rotate the upper and lower case ascii character set */

#include <stdio.h>
#include <ctype.h>

main(argc,argv)
	int argc;
	char *argv[];
{
	int c;
	int rotation;

	if (argc > 1)
	{	if (sscanf(argv[1],"%d",&rotation) != 1) exit(1); /* bad conversion */
	}
	else rotation = 13;
	while (rotation<0) rotation += 26;

	while ( (c=getchar()) != EOF ) {
		if (isupper(c))	{
			putchar('A'+ (c-'A'+rotation) % 26 );
			}
		else if (islower(c)) {
			putchar('a' + (c-'a'+rotation) % 26);
			}
		else putchar(c);
		}
}

-- 

The MAD Programmer -- 919-228-3814 (Cornet 291)
alias: Curtis Jackson	...![ floyd clyde ihnp4 mhuxv ]!burl!rcj