Encrypten en decrypten met persoonlijke sleutel

<?php
    
    class EncryptedString
    {
        var $sKey;    
        var $sData;
        
        function EncryptedString($sData, $sKey)
        {
            $this->sKey = sha1($sKey) . sha1($sKey . substr(sha1($sKey),2,1)); // Create a combined 320 bits key 
                                                                               // 320 bits is save for longer encryption strings    
            $this->sData = $sData;
        }
        
        function Encrypt() 
        {
            
            // Encryp the data by your personal key
            $sResult = '';
            for($i=0; $i<strlen($this->sData); $i++) 
            {
                $char = substr($this->sData, $i, 1);
                $sKeychar = substr($this->sKey, ($i % strlen($this->sKey))-1, 1);
                $char = chr(ord($char)+ord($sKeychar));
                $sResult .= $char;
            }
            
            $this->sData = base64_encode($sResult); // Encode the result into an Base64 string and store it
            
            return $this->sData;
        }

        function Decrypt() 
        {
            $sResult = '';
            $this->sData = base64_decode($this->sData); // Decode the data from Base64
            
            // Decryp the data by your personal key
            for($i=0; $i<strlen($this->sData); $i++) 
            {
                $char = substr($this->sData, $i, 1);
                $sKeychar = substr($this->sKey, ($i % strlen($this->sKey))-1, 1);
                $char = chr(ord($char)-ord($sKeychar));
                $sResult.=$char;
            }
            
            $this->sData = $sResult; // Store the decrypted / original string
            
            return $this->sData;
        } 
    } // End of class
    
    
    
    
    /*
     * USE OF THE ENCRYPT CLASS
     * ------------------------
     * 
     * For encrypting: 
     *   - Create clear string
     *   - Create clear key
     *   - Create EncryptedString object
     *      * @params: string, key
     *   - Call class function Encrypt()
     *      * @return: encrypted string
     * 
     * For decrypting
     *   - Create encrypted string
     *   - Create clear key
     *   - Create EncryptedString object
     *      * @params: encrypted string, key
     *   - Call class function Decrypt()
     *      * @return: decrypted string
     * 
     * 
     */
    
    $sKey = "pHpFRe@kZ"; // The personal key will be transformed to a combined SHA1 key in the constructor
     
     
    // Example of encrypting a string
    $sString = "TOP SECRET";
    $oEncrypt = new EncryptedString($sString, $sKey);
    $oEncrypt->Encrypt(); // returns encrypted string: tYSAWbl5dbd4uA==
    
    // Example of decrypting a string
    $sString = "tYSAWbl5dbd4uA=="; // Encryption of "TOP SECRET"
    $oDecrypt = new EncryptedString($sString, $sKey);
    $oDecrypt->Decrypt(); // returns decrypted string: TOP SECRET
    
    
?>