function decrypt($enc_string,$base64_decode=true){
		if(is_null($enc_string) || empty($enc_string)) return NULL;
		if(!$this->verified) $this->verify();
		//decrypt and return
		if($base64_decode) $enc_string = base64_decode($enc_string);
		$plain_string = mcrypt_decrypt(
			 self::$crypt_cipher
			,base64_decode($this->key)
			,$enc_string
			,self::$crypt_mode
			,base64_decode($this->iv)
		);
		//get size of string from atom
		$size = unpack('N',substr($plain_string,0,4));
		$size = array_shift($size);
		//make sure we have the original string
		$plain_string = substr($plain_string,4,$size);
		return $plain_string;
	}