Basic string encoding/decoding functions

Functions:

These are basic string encoding/decoding functions I developed for use in flat-file databases. They offer limited security to protect sensitive data from being viewed.

Usage:

<?php encode($string,$key); ?> to encode.
<?php decode($string,$key); ?> to decode.

Code:

<?php

function encode($string,$key) {
    $key = sha1($key);
    $strLen = strlen($string);
    $keyLen = strlen($key);
    for ($i = 0; $i < $strLen; $i++) {
        $ordStr = ord(substr($string,$i,1));
        if ($j == $keyLen) { $j = 0; }
        $ordKey = ord(substr($key,$j,1));
        $j++;
        $hash .= strrev(base_convert(dechex($ordStr + $ordKey),16,36));
    }
    return $hash;
}

function decode($string,$key) {
    $key = sha1($key);
    $strLen = strlen($string);
    $keyLen = strlen($key);
    for ($i = 0; $i < $strLen; $i+=2) {
        $ordStr = hexdec(base_convert(strrev(substr($string,$i,2)),36,16));
        if ($j == $keyLen) { $j = 0; }
        $ordKey = ord(substr($key,$j,1));
        $j++;
        $hash .= chr($ordStr - $ordKey);
    }
    return $hash;
}

?>

Example #1:

Encode:
<?php echo encode("Please Encode Me!","This is a key"); ?>

Result:
p3e4e4241674d2r4m4i5o464a4f2p3k5c2


Decode:
<?php echo decode("p3e4e4241674d2r4m4i5o464a4f2p3k5c2","This is a key"); ?>

Result:
Please Encode Me!

Example #2:

Encode:
<?php echo encode("Please Encode Me!","A New Key"); ?>

Result:
t3t5e434q494f2m4s5j5w544b4d2m3k5i2


Decode:
<?php echo decode("t3t5e434q494f2m4s5j5w544b4d2m3k5i2","A New Key"); ?>

Result:
Please Encode Me!