public function encrypt($plain_string,$base64_encode=true){
		if(!$this->verified) $this->verify();
		//add size atom to encrypted string
		$size = pack('N',strlen($plain_string));
		$plain_string = $size.$plain_string;
		//encrypt and return
		$enc_string = mcrypt_encrypt(
			 self::$crypt_cipher
			,base64_decode($this->key)
			,$plain_string
			,self::$crypt_mode
			,base64_decode($this->iv)
		);
		if($base64_encode) return base64_encode($enc_string);
		return $enc_string;
	}