ROT13 in Powershell

Let see if someone would like to talk about this function. You can open your administrative command prompt and type powershell. Copy and paste the following function onto the powershell command line.

Function Rot_num([string]$str, $n)
{
$value=""
For ($index= 0;$index -lt $str.length;$index++){
$ch= [byte][char]($str.substring($index,1))
if ($ch-ge 97 -and $ch -le 109){$ch=$ch+ $n}
else {
if ($ch-ge 110 -and $ch -le 122){$ch=$ch- $n}
else {
if ($ch-ge 65 -and $ch -le 77){$ch=$ch+ $n}
else {
if ($ch-gt 78 -and $ch -le 90){$ch=$ch -$n}
}
}
}
$value=$value+ [char]$ch
}
Return $value
}

After you have pasted the function above, you can start using it to see how it works. Just type rot_num followed by a string and the number 13. Then you can do the same to decrypt the value by typing rot_num encrypted message and the number 13 again. It should decrypt the encrypted message.

PS C:\> Rot_num Hell0Urhere2014 13
             Uryy0Heurer2014
PS C:\> Rot_num Uryy0Heurer2014 13
             Hell0Urhere2014

So, talk about what this code does and what is ROT-13.