1. INTRODUCTION
With the advance in the use of the Internet, the creation of
tools that facilitate the development of applicatory is inevitable,
therefore the search of the technological perfectioning in the
dissemina1c6ao of information through the Internet is each bigger
time. The WWW if has shown one of the used tools more in the Internet
for the dissemina1c6ao of information, as well as the one of greater
and faster evolution.
Together with the use of the WWW, that codifies its pages in
language HTML, diverse types of applicatory had appeared that they had
been integrating its functionalities to the Browser WWW. These
applicatory ones interact with language HTML aiming at to improve the
resources offered for who develop the pages that will be
disponibilizadas in the Internet. The use of Java Applet, that
derived from the Java language, is an example of applicatory that it
was incorporated in language HTML.
For desenvolvedores of WWW pages that are interested in
improving the resources offered for its pages, the applicatory ones
that they had been incorporated in language HTML if they have shown of
great utility, but have who use its potentialities in improper way,
piercing security projects and providing bothering for who it has
access them.
The assignment of hostile executable content will be evident
when after the act of receiving, its execution to try to monopolize or
to explore the resources of the system in an improper way and without
authorization.
A hostile executable content can violate the security
politics and obtain to inside twirl codes native of the machine that
received them, taking the control of the system total.
This type of behavior comes to stand out that the access to
the executable contents for people who are unaware of its
potentialities can be dangerous, therefore who is sailing in the
Internet does not know when its Browser is receiving a content
executable, also being unaware of which it goes to be the result of
its execution.
They are not common tools that obtain to block an attack
whose intermediary is the proper application, that is, the blockade to
an application protocol are not comumente feasible, therefore the
majority of the current projects of protection for on corporative nets
to the Internet does not control this type of access.
The majority of the projects of security for Intranets that
are on to the Internet is based on the Firewalls. They obtain to
block the improper access being based on the filtering of the
protocols of level 3 (Net) and 4 (Transport) of the Model of Reference
ISO/OSI, IP and TCP respectively in the Internet architecture. As an
executable content is part of the application, them they obtain to
have access any machine, being this of an Intranet theoretically
protected by a Firewall or directly on inside to the Internet, since
that the Firewall does not have a filter that it hinders the entrance
of some executable contents for the interior of an Intranet. Exactly
thus attacks that use technologies in set can ignore the filters taxes
for some Firewalls.
2. FUNCTIONAL CHARACTERISTICS OF THE EXECUTABLE CONTENTS
As the technologies used in the construction of executable
contents are several and each one of them possesss proper
characteristics, in the next sessions each one to them is detailed.
2.1 Java Applet
The Java language was developed by the Sun Microsystems to
make possible that applications and Applet could be developed, being
differentiated in the following way: Java applications are developed
to be executed for a Java interpreter, inside of a Java environment
and the Java Applet are executed by a Runtime of the Java language
that is inlaid in the Browsers WWW.
When a Browser receives an Applet to be executed, for the
definitions of security imposed by the language, this Applet would
inside have a restricted execution of the machine of the user, that
is, the act of receiving of Java Applet for the Browser WWW would not
have to cause risks to the machines, importing if this Applet he was
not loaded of an Intranet or the Internet. For its definition the
actions executed for a Java Applet are restricted to an area in the
dedicated Browser WWW to the Applet, being this area called Sandbox.
An Applet can inside make any thing of the Sandbox, but it cannot
read, record or to execute nothing that is it are of the reach of the
Sandbox. The Sandbox aimed at to guarantee that if the user to
receive an Applet hostile, it will not provoke no damage in the
machine. Uma Sandbox is constituted by the following elements:
Characteristics of Security, verification of the ByteCode, ClassLoader
and manager of security.
Characteristics of Security: This part is responsible for
the definitions of functioning of the Java language that will go to
try to hinder that the attacks most common can be applied using
programming artifices. To exemplificar one of the characteristics of
security of the Java language, we can say that a Java programmer will
not be able to forge addresses for the memory, therefore the
allocation and the model of reference of the memory is total obscure,
being controlled for the Runtime system of the platform.
Verification of the ByteCode: When a Java compiler compels a
code source it generates a ByteCode. For the Runtime of the language,
one I break up compiled of code can have come of any part of a net,
and he does not know yourself if the compiler who generated the
ByteCode was trustworthy or not, that is, if it followed or not them
rules of security specified by the manufacturer of the Java Language.
The Runtime of the language simply does not trust the ByteCodes that
they are brought by the net, and submits them it a series of
verifications. These verifications try to guarantee that the code
that will be passed to the Java Interpreter will be apt to be executed
without no problem.