Hi,
This little patch makes caesar(6) useful at both encrypting and
decrypting texts by allowing a negative rotation.
Example:
$ echo Ceci est un test | caesar 10
Moms ocd ex docd
$ echo Ceci est un test | caesar 10 | caesar -10
Ceci est un test
A similar patch was proposed by Dieter Rauschenberger in 2008 with
little response so perhaps explaining why this is useful will help.
Without spoiling too much: one of the puzzle in the Infocom game Leather
Goddesses of Phobos requires to decipher such a text.
I did not touch the man page as it was unclear about rotation boundaries
anyway.
Regards.
Index: caesar.c
===================================================================
RCS file: /cvs/src/games/caesar/caesar.c,v
retrieving revision 1.20
diff -u -p -u -p -r1.20 caesar.c
--- caesar.c 10 Aug 2017 17:24:30 -0000 1.20
+++ caesar.c 15 May 2019 14:34:49 -0000
@@ -80,7 +80,7 @@ main(int argc, char *argv[])
printit(13);
if (argc > 1) {
- i = strtonum(argv[1], 0, 25, &errstr);
+ i = strtonum(argv[1], -25, 25, &errstr);
if (errstr)
errx(1, "rotation is %s: %s", errstr, argv[1]);
else
@@ -134,7 +134,9 @@ void
printit(int rot)
{
int ch;
-
+
+ if (rot < 0)
+ rot = rot + 26;
while ((ch = getchar()) != EOF)
putchar(ROTATE(ch, rot));
exit(0);
