Basic encoding function gone wrong

[748323]

I'm making an encoding function, but it went wrong already. I know that this would be very easy to crack, but it will become a lot more complicated later on.

Pretty much, the code declares the variables, changes them into arrays, and uses Str_replace to replace all instances in $_GET['x'] with another. "a" with "f", "b" with "c", etc.

But, it doesn't work that way. When I tell it to encode "a", it returns "2". When I try to encode "abcdef", I get "2U#dt2", instead of the results I wanted, which is "f)tIk^". Thanks.

<?

$abc = "abcdefghijklmnopqrstuvwxyz1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ!@#$%^&*()_-+=";
$key = "f)tIk^PQoOhzNJw9-_6ebs!4pxRaEqT$U2LWd07FGl&BZVy3+7#rm=M%5*jYXvD(AcHu1CKn@IgS";

for($i=0; $i < strlen($abc); $i++) {
	$x = $i + 1;
	$abc_array[] = substr($abc, $i, 1);
	$key_array[] = substr($key, $i, 1);
}


$enmsg = str_replace($key_array, $abc_array, $_GET['x']);

echo $enmsg;

?>

 

[jpadie]

have slightly changed the code to give the effect you wanted.

$abc = "abcdefghijklmnopqrstuvwxyz1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ!@#$%^&*()_-+=";
$key = "f)tIk^PQoOhzNJw9-_6ebs!4pxRaEqT$U2LWd07FGl&BZVy3+7#rm=M%5*jYXvD(AcHu1CKn@IgS";
$_GET['x']="now is the time for all good me to come to the aid of the party";

for($i=0; $i < strlen($abc); $i++) {
    $key_array[substr($abc, $i, 1)] = substr($key, $i, 1);
}

$encoded = "";

for($i=0; $i < strlen($_GET['x']); $i++) {
	$k = substr($_GET['x'], $i, 1);
    $encoded .= $key_array[$k];

}


echo "The message is " . $encoded;

?>

 

[748323]

Can you please explain how your code works? Also, why doesn't mine work as expected? Thanks a lot. I will look into your code and try to understand it, though.

 

[jpadie]

in pseudocode the array structure is
array[key]=>array[value]

the first foreach loop assigns the encoded value to each array[value] for array[key]. thus array['a'] = array['f'] in your example.

i believe that this is where you were going wrong as you were merely creating two arrays with numeric keys.

the second foreach loop iterates through the incoming _GET variable and sets a new variable equal to the encoded value which is the value assigned to the key that equals the character of the _GET var [sorry - it's easier to explain in the code...]. thus if letter 5 of the _GET var is an "X" then the encoded value will be $key_array['X']

lastly i don't think that you can use str_replace in the manner you did, (given the inputs you had).

hth
Justin

 

[jpadie]

I've had another look at your code. one serious mistake you made was the reversal of the search and replace keys in the str_replace function.

i think that there are also issues with some of the characters in your search string (the carat seems to cause problems). as a result if you print_r both of your arrays then you find that there is a large number of keys that are unfilled in the key array.

debugging your code i took things right back to basic and got the following to work just fine.

<?
$abc = "abcd";
$key = "f)tI"; 
$x="abcd";
echo "<br><br><br>";

for($i=0; $i < strlen($abc); $i++) 
{
    $abc_array[] = substr($abc, $i, 1);
    $key_array[] = substr($key, $i, 1);
}
print_r ($abc_array);
echo "<br>";
print_r ($key_array);

$e = str_replace($abc_array, $key_array, $x);
echo "<br><br>results: $e";
?>