-----Original Message-----
From: Gordon Low [mailto:[EMAIL PROTECTED]
Sent: 09 March 2004 08:29
To: [EMAIL PROTECTED]
Subject: Logical problem with small script??
Wondered if anyone can throw some light on why this script won't act
properly.
Wrote it to convert a string using a ceaser cipher for a course I am
doing. Basically get the string and replace each character with the
character offset by 3 or 4 up to 26. Have to try up to 26 times so it
was crying out for a script, trouble is it doesn't work the way I
intended and I cannot see how.
No real attempts at error catching have been done as it was only
supposed to be used by myself.
Supposed to do this
Enter
>cipher.pl phhw dw plgqljkw
...and get all 26 different combinations to crack the message.
Trouble is I get this.....
qiix ex qmhrmklx -------> offset = 1 <-------
qiix ex qmhrmklx -------> offset = 1 <-------
rjjy fy rnisnlmy -------> offset = 2 <-------
qiix ex qmhrmklx -------> offset = 1 <-------
rjjy fy rnisnlmy -------> offset = 2 <-------
skkz gz sojtomnz -------> offset = 3 <-------
qiix ex qmhrmklx -------> offset = 1 <-------
rjjy fy rnisnlmy -------> offset = 2 <-------
skkz gz sojtomnz -------> offset = 3 <-------
tlla ha tpkupnoa -------> offset = 4 <-------
Instead of just going through once it is repeating ie loops to 1 then
loops to 2 then loops to 3 up till loops to 25. Cracks the message ok at
offset 23 but I don't want it looping all the time. Code follows, I am
on Linux 8.0 with Perl 5.8, there is probably better ways to do this but
it is driving me mad trying to see the logical problem, hoping someone
can help.
*******************************************************************
#!/usr/bin/perl -w
use strict;
my @alpha =
("a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s"
,"t","u","v","w","x","y","z");
my %alphat;
my $count;
my $ceascount;
my $op = "";
foreach (@alpha){ # set up a lookup table for the array
offset
$alphat{$alpha[$count]} = $count;
$count++;
}
for ($ceascount = 1; $ceascount < ($#alpha +1);$ceascount++,print
$op){ # try all ceaser cipher offsets
foreach (@ARGV){ # take in each command line arg
for ($count=0; $count < length($_); $count++){ # go through
each arg and convert with cipher
$op .= $alpha[($alphat{substr($_,$count,1)} + $ceascount) %
($#alpha+1)]; # conversion
}
$op .= " "; # space between args
}
$op .= " -------> offset = $ceascount <-------\n"; # final result
} # use another ceaser cipher offset
*******************************************************************
Hi Gordon,
The problem here not really the logic of the script. Each time you loop
through on the outer for loop $op is being appended to, not over written.
Each time though the loop you are processing a different offset but printing
that and all previous ones.
To fix this simply move the line my $op = ""; to be the first line inside
the outer for loop and move the print to the end of that loop.
for ($ceascount = 1; $ceascount < ($#alpha +1);$ceascount++)
{
my $op = ""; # This means $op is empty each time through
foreach (@ARGV)
{
for ($count=0; $count < length($_); $count++)
{
$op .= $alpha[($alphat{substr($_,$count,1)} +
$ceascount) %($#alpha+1)];
}
$op .= " ";
}
$op .= " -------> offset = $ceascount <-------\n"; # final result
print $op,"\n";
}
Alternatively move the print to outside the loops all together. ie only
print once.
for ($ceascount = 1; $ceascount < ($#alpha +1);$ceascount++)
{
foreach (@ARGV)
{
for ($count=0; $count < length($_); $count++)
{
$op .= $alpha[($alphat{substr($_,$count,1)} +
$ceascount) %($#alpha+1)];
}
$op .= " ";
}
$op .= " -------> offset = $ceascount <-------\n";
}
print $op,"\n";
Hope this helps,
Jim
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