Encryption decryption problem

[computerzworld]

I am having one php function which encrypts the string using custom encryption. I am trying to decrypt the string using its reverse function but I am unable to do so. Here is the function which encrypts the string.

function encrypt($str)
{
    $cReturn = "";

$newStr = trim($str);
$len = strlen($newStr);

$j =0;

for($i=0;$i<$len;$i++)
{
    $j++;

    $cTemp = substr($newStr,$i,1);

    if(in_array($cTemp,range(1,9)))
    {
        $cTemp = chr(64 + intval($cTemp));
    }

    $cReturn.= chr(ord($cTemp) + $j);
}
return $cReturn;
}

What should be the reverse function of it? Please help me. Thanks in advance....

[NogDog]

I'm not going to take the time right now to figure it out for you, but I will take the time to ask, "Why reinvent the wheel?" PHP has built-in access to a number of encryption methods which are based on algorithms invented by experts in the field, are most likely much stronger encryptions than what you are trying to implement, and have been tested and optimized.

[computerzworld]

ya you are absolutely right but I am provided one algorithm which is used to encrypt the string & I need to decrypt the same using reverse algorithm but I am unable to do it....

[NogDog]

One problem I see is that you cannot differentiate between the numbers 1 through 9 and the letters A through I:

echo encrypt("123456789");
echo "<br>";
echo encrypt("ABCDEFGHI");

Both lines will be "encrypted" as "BDFHJLNPR". Off-hand I see no way to tell whether any character that gets decrypted to a letter in the range A-I is supposed to be that character or a digit from 1-9, other than perhaps some sort of spell-checker/dictionary look-up sort of thing.

[NogDog]

Here's the best I can do without an idea on how to resolve the problem with the digits 1-9:

<?php
function encrypt($str)
{
    $cReturn = "";

$newStr = trim($str);
$len = strlen($newStr);

$j =0;

for($i=0;$i<$len;$i++)
{
    $j++;

    $cTemp = substr($newStr,$i,1);

    if(in_array($cTemp,range(1,9)))
    {
        $cTemp = chr(64 + intval($cTemp));
    }

    $cReturn.= chr(ord($cTemp) + $j);
}
return $cReturn;
}

function decrypt($str)
{
   $result = '';
   for($i = 0, $len = strlen($str); $i < $len; $i++)
   {
      $j = $i + 1;
      $result .= (chr(ord($str[$i]) - $j));
   }
   return($result);
}

// TEST
$test = "ABCXYZ abcxyz 123789";
echo "<pre>";
echo encrypt($test);
echo "\n";
echo decrypt(encrypt($test));
?>

Output:

BDF\^`'ikmƒ…‡.PRTY[]
ABCXYZ abcxyz ABCGHI

[computerzworld]

thanks for the reply... i will try to figure it out.... thanks once again....