src/Zend/Filter/File/Encrypt.php
public function filter($value)
    {
        if (!file_exists($value)) {

            throw new Zend_Filter_Exception("File '$value' not found");
        }

        if (!isset($this->_filename)) {
            $this->_filename = $value;
        }

        if (file_exists($this->_filename) and !is_writable($this->_filename)) {

            throw new Zend_Filter_Exception("File '{$this->_filename}' is not writable");
        }

        $content = file_get_contents($value);
        if (!$content) {

            throw new Zend_Filter_Exception("Problem while reading file '$value'");
        }

        $encrypted = parent::filter($content);
        $result    = file_put_contents($this->_filename, $encrypted);

        if (!$result) {

            throw new Zend_Filter_Exception("Problem while writing file '{$this->_filename}'");
        }

        return $this->_filename;
    }
public function filter($value)
    {
        if (!file_exists($value)) {

            throw new Zend_Filter_Exception("File '$value' not found");
        }

        if (!isset($this->_filename)) {
            $this->_filename = $value;
        }

        if (file_exists($this->_filename) and !is_writable($this->_filename)) {

            throw new Zend_Filter_Exception("File '{$this->_filename}' is not writable");
        }

        $content = file_get_contents($value);
        if (!$content) {

            throw new Zend_Filter_Exception("Problem while reading file '$value'");
        }

        $encrypted = parent::filter($content);
        $result    = file_put_contents($this->_filename, $encrypted);

        if (!$result) {

            throw new Zend_Filter_Exception("Problem while writing file '{$this->_filename}'");
        }

        return $this->_filename;
    }
Defined by Zend_Filter_Interface

Encrypts the file $value with the defined settings

@param  string $value Full path of file to change
@return string The filename which has been set, or false when there were errors