The CodeBase Attribute
Earlier lessons discussed briefly some of the
processes involved in downloading controls via the Internet, and the security threats
posed by the shared nature of the Internet. In this chapter, you will learn about the
actual process of installing Internet components and a few ways to prevent the
installation of unwanted code or content. This process involves three stages:
- First, the control is downloaded to the local
- Second, the control undergoes a verification process
to ensure its integrity.
- Finally, the control is installed onto the machine
and added to the system registry.
The following sections of this chapter define these
steps, and describe, in greater detail, the various application program interfaces (APIs)
that apply to them.
ActiveX objects within an HTML document go through
several stages before they are installed on a user's local machine.
The first step, the downloading or acquisition of
the component, can happen in a couple of different ways. A few of these ways (as they
relate to the Web) were discussed earlier, ( when installing an application such as
Internet Explorer, for instance). Remember however, in this network-centric lesson, that
ActiveX controls can be installed via floppy disks, data tape, and so on. The usual method
of installing these components, however, is from within an HTML document via an ActiveX
Web browserusing the <OBJECT> tag.
The second step, verification , can use any or none
of the following steps (installation and component downloading) to ensure that the control
will not act maliciously on your system. Because the verification process is not
mandatory, each individual user, programmer and administrator must decide which, if any,
of the processes will be used.
The third step, installation, depends on which
selected verification process the control has successfully passed through. Even if a
control has no programmed security features, users will be prompted on whether or not they
wish to install that object. This is because objects with no security features cannot
identify themselves as safe.
Not every installed object is necessarily be an OLE
object. When the object is an OLE control, there are several considerations for ensuring
There are two primary HTML tags that can be used to
download an item from the Internet : <OBJECT> and HREF.
Minimal security via ActiveX is available within the
HREF tag because HREF is treated as a hyperlink rather than an OLE object. An example of
this would be a CGI server script; the hypertext reference would look like the following:
<A HREF="http://www.domain.net/CGIScript.exe">CGI Script</A>
The browser, treating CGIScript.exe as a hyperlinked
document, would download and launch the .EXE without conducting any real security
To enable the majority of ActiveX security features,
you must identify an item as an object. (CGI scripts are not normally OLE objects).
Identify the item as an OLE object using the <OBJECT> tag.
This site is Microsoft's display gallery for their ActiveX controls. You can observe the
code download and verification processes in action as you download the controls from this
The CodeBase Attribute
After identifying an object via the <OBJECT>
tag (and setting its parameters if necessary), use the CodeBase attribute of the
<OBJECT> tag to inform the user's system of the location of the control. The format
of the Code attribute closely resembles the format for any URL:
As time goes by, computer programs are either phased
out or, preferably, upgraded. This can cause some problems with conflicting versions of
the same control. When a software manufacturer decides to upgrade its control,
applications or scripts written around that code might not work with versions other than
the one for which it was written. To manage the installation of different versions of the
same control, the Code attribute enables content providers (HTML authors) to specify which
version their page needs.
This version identification information is tacked
onto the end of the Code URL in bold in the following example:
Using this attribute, you can identify all versions
for which your application is usable. If your application was written for Version 1 and is
still usable with Versions 2 and 3, the preceding example is how you should format the
attribute. If the user has Version 1 installed on his machine, his browser will attempt to
obtain the most recent version specified (here, Version 3) when it hits this tag.
For the most part, software vendors try to keep their products backwards compatible. This
allows users of the product to perform minimum modifications to their programs when a
control is upgraded. One example of this is the evolution of Visual Basic.
Basic began gaining wide acceptance before object-oriented programming was very popular.
These early versions of Basic used line numbers and REM statements. During this time, the
first major burst of growth in the training, education and employment of programmers was
occurring. As a result, the bolus of programmers used these features to identify the
location of subroutines, or to identify a line of text as a comment, to be ignored by the
As Visual Basic came into being, REM statements were replaced by the apostrophe ('), and
the use of line numbers to maintain the sequence in which code was to be executed became
To maintain backwards compatibility, the choice between long and short commands was made
an option. A programmer could use the simple apostrophe to identify a remark, or he could
use the REM statement. To the compiler, they are the same. Line numbers also became
By allowing programmers to use these conventions, Microsoft ensured that a programmer who
spent days or months or years developing an application could still use all or most of his
code in the new programming environment. This is backwards compatibility .
.CAB and .INF Files
There are several types of objects that can be used
as ActiveX objects within the <OBJECT> tag of an HTML document. Each object has its
own specific features and drawbacks:
- .CABCompressed cabinet file
- Portable Executables (PEs)(.OCX: custom
control; .EXE: standalone executable; .DLL: dynamic link library)
- .INFSetup information file
.CABCompressed Cabinet Files
For you hard-core hackers out there, the compression type used for .CAB files is based on
the Lempel-Ziv compression algorithm. This is a "lossles" algorithm that was
developed in 1977. Where some other compression algorithms look for whitespace, Lempel-Ziv
looks for repeated binary sequences. Then it uses an offset value to refer to the first
instance of the sequence.
About the time Windows95 was released, users began
seeing .CAB files on a variety of Microsoft products' installation disks. The ActiveX SDK
includes a tool, diantz.exe which is used to create these active archives. Active
means that the archives have more power and utility than the previously popular shareware
compression standards (such as ZIP, LZH, ARJ, ARC, XX_ and so on).
With the CABView utility (available in the Windows95
PowerToys on the enclosed CD), users can double click a CABinet file to make their system
view and treat the archive as a subdirectory of its current directory. Drag and drop,
execution of PEs, and file editing are all supported within a CABinet.
Now you're going to learn how to use Microsoft's two
command-line utilities for working with cabinet file compressionDiantz.exe and
Extract.exe. These can be found in the \InetSDK\bin directory.
Diantz.exe is the utility for creating .CAB
files . It's very easy to use from a prompt. Simply follow .exe with the name of the file
you want to add to a cabinet, and the name of the cabinet to which you want the compressed
The Diantz Utility
Diantz source destination Diantz /F directive_file
The Diantz utility is used to create and update compressed file .CABinets.
There are two methods that can be used with this utility. The first is to add files one by
one like so:
Diantz.exe MyFile.dat MyCab.cab
This would add MyFile.dat to MyCab.cab, creating MyCab.cab if it doesn't already exist. If
you don't specify a .CABinet file, it'll just compress the file alone, and name the
compressed file the same as the original, except that the last character will be an
The other way is to use a directive file on the command line like so:
Diantz.exe /F MyDirec.ddf
This will build the .CABinet according to the instructions in the Diamond directives file
Several other command-line parameters can be used with either of these methods, including
/V#Where # is the level of verbosity (1-3)
/D VAR=MyValuethis sets the environment variable VAR to the value in MyValue
/L DIRwhere DIR is the destination directory for the archive
The name of the file in the InetSDK is Diantz.exe, but if you type the .EXE name alone at
a prompt, you will see that it returns the help information for a command called
Diamond.exe. You might want to rename Diantz.exe to Diamond.exe because that's the file's
This is the utility used for extracting files
from a .CAB file. It is also very simple to use from a prompt. Just follow .exe with the
name of the .CABinet from which you want a file extracted, and the name of file.
The Extract Utility
Extract cabinet file
The Extract utility is used to extract files from compressed file .CABinets. To use it,
follow the executable name with the name of the compressed cabinet and the name of the
file you wish to extract, like so:
Extract.exe MyCab.cab MyFile.dat
This will extract the file MyFile.dat from the cabinet MyCab.cab.
Lets try an example of the Diantz.exe and
Extract.exe cabinet manipulation utilities.
First, create a direcotry within which to work.
Let'suse a directory called \CabZip\
on the C drive.
You can find an example of the files with which we will be working on the CD-ROM in a
similarly named directory.
Next, make sure that the Diamond compression utility
(Diantz.exe) is available within this directory. Since this utility is in the
\INetSDK\Bin\ directory, just make sure its in the path. To verify that Diantz.exe
is in the path and available from within any directory, type path at the DOS command
prompt. If you do not see the \INetSDK\Bin\ in the list of directories returned by the
path statement, add a line to your autoexec.bat file as follows:
This appends the \InetSDK\Bin\ directory to your
default program search path. Make sure this statement is on a line after all other path
statements in your autoexec.bat. This ensures other directories are searched first. This
way, as your programs become updated (and they will!), the \INetSDK\Bin\ directory will be
the last place your system looks for a program that it cant find elsewhere.
The next step is to copy the files from the CD-ROM
into this new directory. The files are listed in the following table:
Table 17.1. CD-ROM files .
||and that's done with.wav
||OLE-OCX ActiveX Programming.mcc
||VB Internet Controls News.url
Next, create a cabinet for each file. Place each
file in its own cabinet to observe the compression ratios for the different kinds of
This demonstration shows that text-based and bitmapped files compress very well. On the
other hand, binary files, such as audio applications, dont compress as well. Also,
once you have created a cabinet (or used any other form of compression on a file), you
will not be able to compress it again to reduce it further.
To make this compression process go a little faster,
you can create the following batch file
(a sample has already been created on the CD-ROM
diantz /v3 "ActiveX.ccc" activex.cab
diantz /v3 "Alice1.jpg" alice1.cab
diantz /v3 "Cheshire.avi" Cheshire.cab
diantz /v3 "resume.doc" resume.cab
diantz /v3 "Office95.xls" Office95.cab
diantz /v3 "OLE-OCX ActiveX Programming.mcc"
"OLE-OCX ActiveX Programming.cab"
diantz /v3 "VB Internet Controls News.url"
"VB Internet Controls News.cab"
diantz /v3 "and that's done with.wav"
"and that's done with.cab"
Notice the quotation marks (") around some of the files. When working from a DOS
command prompt, it is often necessary to place these marks around files with long
filenames, long file extensions, case sensitivity and embedded spaces.
Next, extract each one of the cabinet files. If you
extract them into the current directory (where copies already exist), you will be prompted
as to whether you wish to overwrite the current copy or not. To automate this process,
create a batch file with the following command (a copy of this batch file, named
CabUnZip.bat is in the \CabZip\ directory on the CD-ROM):
for %%x in (ACTIVEX.CAB ALICE1.CAB CHESHIRE.CAB RESUME.CAB OFFICE95.CAB OLE-OC~1.CAB
VBINTE~1.CAB ANDTHA~1.CAB) do extract.exe %%x
Type the whole thing on one line. Perform this
function from the command prompt as well as from within a batch file. From a prompt,
replace the batch variable identifier (%%) with a command line variable identifier (%).
The .OCX, .EXE and .DLL files are referred,
collectively, as PE (Portable Executable) files. These files are the simplest to use as
ActiveX controls because they require no other files (that is, they are standalone
utilities) and they can be run automatically.
A PE cannot be cross-platform compatible. It can
only run on the machine type for which it was compiled. For this reason, content providers
who use PEs as embedded objects need to consider the type of machine with which their
users will be accessing the document.
Over a distributed environment such as the Internet,
these BLOBs (Binary Large Objects) can take a long time to download. If the code is tight,
or the file is compressed using a compression algorithm, this significantly reduces the
amount of time it takes to download them. But if the file is compressed, it can not be
self-executing. It must first be uncompressed, or returned to its original form. The
exception to this is .CAB filesthey can be self-executing when used as ActiveX
.INF files are used to tell the local machine how to
setup the control and where to get its components. By specifying the files that various
machines might need (such as Mac, UNIX, Win95), the .INF file can be used to install a
different package for each type of system.
These .INF files are very similar to the old .INI
; Setup File for Sample.INF
Referring to the preceding sample .INF file, note
that when launched by an ActiveX browser, the commands within an .INF file would install
two files: sample.ocx and sample.dll. The .OCX would be retrieved from www.domain.net,
while the .DLL would come from the same directory as the .INF (because no external site or
directory was specified). The destdir setting has 2 options: 10 for the Windows directory,
and 11 for the Windows\System directory. If no destination directory is specified, the
control is kept in a cache until purged by automatic (that is space-saving) or manual
You can also see in the sample that the file version
is 18.104.22.168 (note that commas are used instead of dots in the .INF file version settings).
If the machine has version 0.9 installed, it will still download the newer version. If,
however, the local machine has a newer version, 22.214.171.124 for instance, it will not bother
to install the older version. That would be a bug.
An attribute of the <OBJECT> tag, called the
CODETYPE attribute , can be used to further inform the system about the object's
requirements. CODETYPE identifies the object's MIME type. An example of the CODETYPE
attribute, defining an audio-video interface animation would look like this:
ActiveX uses another MIME type to identify the
machine for which the code was written.
This feature of the Code tag is perhaps one of the
most exciting. The Holy Grail of programming has been the use of one program on a variety
of systems. Although this is still not possible (and probably never will be), features of
the Code tag do allow the user's machine to retrieve a copy of the control, designed for
the user's individual systemwhether it is a Mac, UNIX box, PC, or whatever. The
format for this is a MIME type that conforms to the following specification:
where the options for each field include:
FileType - pe, cabinet or setupscript
OS - win32 or mac
CPU - x86, ppc, mips or alpha
Referring to the preceding sample, note that this
MIME type format is extended to allow an .INF file to specify which files would be
required on different machines. In this example, the controls for a Win95 MIPS machine
would be in Win95.cab, the controls for a WinNT Alpha machine would be in WinNT.cab and
the controls for a Macintosh are in MAC.cab. In each case, the entire cabinet would be
downloaded, but only the necessary files would be installed. Also, it keeps a Mac from
having to download the code for a PC and vice-versa.
The threats to system security manifest themselves
in three items: OLE objects, non-OLE objects, and document content. The first two are of
primary significance to the system developer. The last, document content, allows parents,
employers and other individuals to determine the type of content their users view, without
actually censoring every item their users can accessan impossible task.
Prior to ActiveX, the installation and configuration
of software was completely controlled by the user or his system administrator. Now,
through simply looking at a Web page, a control or other object can find its way to the
user's machine with very little user interaction. This exposes the user to the threat of
malicious or simply undesirable code being installed on their local machine.
Internet Explorer, Netscape, and most other browsers
allow the users, not the system administrator, to select the level of security they wish
to observe. Internet Explorer ships with the highest level of security enabled by default.
Some users disable their security features to avoid those pesky confirmation dialog boxes.
You might want to think twice before disabling any of them.
Although a determined hacker can still create a Web
page that gives the user this kind of grief, the use of ActiveX security measures helps
ensure that the developer of the code is identifiable. In the event that the developer's
software creates an undesirable effect, the user will have information to contact him and
inform him of his code's apparent bugs.
Another feature of ActiveX security is that it
allows users to determine whether they want to install a piece of code in the first place.
If the control does not have security features enabled, the user is told that the code
might not be safe, and prompts him as to whether or not he wants it installed on his
machine. If the security features are enabled, it gives the user's machine certain
information about the code and its developer, and that information is verified over the
Net through certifying authorities such as Dun & Bradstreet or GTE.
See trust verification in action when you visit
Microsofts ActiveX control site at http://www.microsoft.com/activex/controls.
When you download a page with an ActiveX control that is not already installed on your
system, Internet Explorer begins downloading the control to your cache (see Figure 17.1).
When the control has been retrieved, another window pops up, asking if you want to install
the control and informing you of any security certificates it contains (see Figure 17.2).
Figure 17.1. When
downloading an ActiveX control, several things happen in Internet Explorer.
Figure 17.2. After an
ActiveX control is downloaded, a pop-up window appears.
Companies such as Verisign have Web sites set up to allow individuals and companies to use
their trust verification services to issue and validate digital IDs.
Finally, ActiveX security has a feature called
Internet Ratings , which provides a degree of parental, administrator or employer control
to define which sites are not to be accessed by their users. Web page developers can place
code within their HTML pages or their ActiveX controls to inform systems that attempt
access about the any risque[as] content on that page. Administrators can then determine
what level of freedom their users have in accessing pages with various levels of violent
or sexual content.
On the enclosed CD-ROM, a directory called \Ratings\
contains several HTML files. If you load the ratings.aspl file into Internet Explorer, you
can view different pages with the ratings system enabled on them. For more information
about having your site rated, you should contact a ratings service.
When you buy a software product off the shelf at
your local store, you have certain assurances that the product will perform as stated on
the box. This assurance (or "Implied Warranty of Merchantability") comes in the
form of a product logo. Microsoft uses a very high-tech hologram to mark its products. If
a knock-off artist wants to copy a Microsoft product and sell it on shelves, he would need
more than a simple printing presshe'd need a hologram copying program as well (or a
box of Microsoft hologram stickers).
This logo-on-a-box method is not as easy to do with
software that is distributed via the Net. Instead, several other methods of verifying
security come into play in ActiveX programming. Information for verifying authenticity and
integrity is contained within the object itself. It might come in the form of X.509
security certificates or other embedded information.
Base Security Layer
Microsoft's Base Security Layer SDK provides the
means whereby a control can be certified as safe. This happens through the System
Certificate Store. I will only briefly discuss the System Certificate Store here. The full
specification can be found in the ActiveX SDK in the \INetSDK\Help\Security\BSLH
When you download and install code that has a
Certificate of Authenticity, this software vendor's certificate is stored in the local
machine's System Certificate Store. Certificates from a variety of vendors can be found
Some of the API calls for accessing this store are
- WinGetSystemCertificateStoreReturns a handle to
the local System Certificate Store.
- WinInsertCertificate or CertStoreAddCertAdds a
new certificate to the System Certificate Store.
- FindCertificateByIssuerNameQueries the System
Certificate Store for a certificate issued by a certain agency.
Using these API calls, a programmer can query the
Base Security Layer for the existence of a security certificate, and retrieve the
information within that certificate to validate a control or controls as authentic. This
certificate is used by the trust verification service.
Trust verification service is the set of API calls
that determines whether a requested object can be trusted. It provides features whereby a
trust administrator can define what is and is not allowed to be installed on a machine.
It also provides a means whereby the administrator
of a system can define the types of processes, controls and other objects that will be
allowed. Although the security certificate will provide information about an object, it is
still up to the trust administrator to make the final call.
To take advantage of trust-verification services,
the trust administrator must work with a trust provider. This provider maintains a server
or group of servers that provides authentication of certificates. This provider determines
the methods used in validating a certificate, thus freeing users and their system
administrators from the complexities of producing and verifying trust certificates.
When an application on a user's machine attempts to
use an object that requires trust verification, the service contacts the software
provider, their agent and/or any other trust providers to validate or update the
Now that you know a little about the
behind-the-scenes processes used to identify safe objects, let's go into how local users
and administrators can implement these features in their own systems. As I stated earlier,
security of all kinds boil down to a few basic features: UserID, Password and,
occasionally, physical location. Still, these can be very powerful when any or all of them
are kept secret.
The Safety API has its first implementation in the
Microsoft Internet Explorer. Users can designate the degree of security they wish to
observe by selecting the Security tab of the View|Options menu in MSIE and pressing the
Programs button (see Figure 17.3). The three options are
- ExpertEvery control that is marked as safe
requires the user to decide whether it will be loaded. Controls that are not marked as
safe can not be loaded.
- NormalOnly controls marked as safe will be
loaded; the user will be prompted to load unmarked controls.
- NoneNo warnings...no security.
Figure 17.3. Internet
Explorer configuration menu to select the level of security.
The complexities of ActiveX security boil down to
two basic questions:
- CreationIs this control still safe when
- InitializationIs the control, standing alone,
The Safety API provides the means to evaluate these
hazards during creation and initialization.
Control Still Safe When Scripted?
When creating an OLE control , programmers define a
set of interfaces with which they want that control to operate.
An example of this type of safe control is the
Marquee control. Its only function is to display animated text in a box. There is no way
for this cutesy little display to harm your machine, so it is safe with any code.
An example of a potentially unsafe control is the
SMTP control from the Internet Control Pack. This control could be scripted to send an
e-mail resignation letter to your boss, or worseyour spouse!
To identify the control as safe for scripting, add
it to the CATID_SafeForScripting Component Category in the system registry. Additionally,
you can add code to the control's internal registration and unregistration routines to
ensure its management in the proper Component Category.
the Control, Standing Alone, Safe?
Controls go through several phases, each having its
own risks and strengths.
When controls are first created (or initialized) on
a system, certain properties define them. In turn, these properties are defined by the
data from an IPersist* interface. The data in this interface can come from just about
anywhere, including some remote server.
The danger here is twofold: the control can
initialize in an undesirable way, or worse, it can send your private data to an untrusted
To identify the control as safe for initializing,
add it to the CATID_SafeForInitializing Component Category in the system registry.
A more versatile, although higher level, method that
works with registry settings is the IObjectSafety interface . In addition to marking a
control as safe or unsafe, it can be manipulated programmatically to command a control to
change its safety level.
To make a control safe for initializing, set the
SetInterfaceSafetyOptions of this interface to INTERFACE_SAFE_FOR_UNTRUSTED_CALLER.
To make a control safe for scripting, set the
SetInterfaceSafetyOptions of this interface to INTERFACE_SAFE_FOR_UNTRUSTED_DATA.
Of course, a particularly brilliant and malicious
programmer can build, rebuild, or reverse-engineer any control to report itself as safe
for scripting, and cause all kinds of damage. That makes trust verification of the source
of the control all the more important.
The Code-Signing Tool
The ActiveX SDK includes a set of tools to assist
the programmer in signing code as safe. This reduces the preceding complex steps to a few
simple steps. This kit helps the programmer certify PEs, cabinets, controls and class
This tool kit uses public key encryption and digital
signatures to determine both the true source of a control and the integrity of that
control (because it was released by the source). The following details each step required
for signing a control as safe.
- Obtaining a *.CER (X.509 certificate)Before you can
digitally sign your code, you must obtain a software publishing certificate through a CA
(certification authority) such as Microsoft or GTE, or through an LRA (local registration
agency) such as your employer or university. The CA determines whether you are who you say
you are, and issues an X.509 certificate, with the public key that you provided embedded
within it. The certificate also has additional information embedded within it identifying
your organization. Distribute this certificate with all signed software.
A control author can choose from two levels of certification. Other levels might present
themselves in time , but the current choices are individual certification or commercial
To obtain individual certification, an applicant needs only to submit positive
identification (as defined by the CA), and promise that the software he publishes won't be
To obtain commercial certification, software vendors must complete the steps required for
individual certification, but must also obtain a D-U-N-S[rm] number from Dun &
Bradstreet, and must generate and store a private key on a dedicated piece of hardware.
For training purposes, the ActiveX SDK includes a utility called MakeCert.exe, which
generates a test (that is, not real) x.509 certificate under your name, and generates a
public and a private key (also known as a keypair). The makecert Utility will then
generate a *.CER (certificate) file.
- Obtaining an .SPC (Software Publishing
Certificate)When you obtain an X.509 certificate, you will use the Cert2SPC.EXE
utility to generate a Signed-Data object in the PKCS#7 format (Private Key Cryptography
Standard #7). This object contains information from however many certificates you want to
use (you can use more than one certificate to sign code if you like).
- Signing a FileThe SignCode Wizard walks you through
the steps of adding your digital signature to your code. When you complete this step, you
can begin to distribute your signed code safely over the Net.
When a user whose ActiveX security features are enabled loads a page that has one of your
signed objects (OCX, DLL, EXE, CAB or class), a dialog box will prompt them as to whether
they wish to load your object. When this dialog appears, it will contain information you
specified when you created the .SPC file. This could include your name, address, phone,
Web site, logo and a variety of information. When you have gone completely through the
wizard, you will ba able to sign your controls and code using public key encryption (see
- Determining File IntegrityWhen you have distributed
your signed code, there is no guarantee that someone will not corrupt your code and
distribute it with the public key signature. If one of your users reports a bug and you
think the fault lies with a hacker (instead of your program), obtain a copy of that user's
suspect code. Then test it to determine its integrity.
The ChkTrust utility can tell you whether your code has been tampered with. It does this
by extracting the PKCS#7 object from the file and extracting the X.509 certificate from
that. It then creates a new hash, and checks it against the one in the PKCS#7 object.
If the hash (digital signature) created with both the public and the private keys is
deemed valid, the suspect program is proven to be the same as the one that the author
originally distributed. If one or both of the signatures is found to be invalid, than the
code is proven to have been altered.
DoUse the MakeCert Utility to generate pretend certificates.
Don'tContinue to use the MakeCert Utility after you obtain a real certificate from
an LRA or CA.
Figure 17.4. The processes
behind public key encryption go through many levels to ensure integrity.
Public Key Encryption
To be confident that your code is safe, you should know a little about the theory and
process behind public key encryption. It is actually little more than a password-protected
password. You must know the first password (the public key) to get the second password
(the private key). The process is shown graphically in Figure 17.2.
As simple as that sounds, its use over the last five years has prompted several government
agencies to consider restricting it.
In simple terms, public key encryption takes an item through several steps:
- A user makes up a passwordthis can be as small
as a word or as large as a passage from a guide.
- The user creates an object that he wishes to encrypt,
such as a letter to his bank.
- The user invokes a routine that creates a
cross-section (or hash) of the object. This routine (such as an RSA scheme) might
read every 4th character, or every even-numbered character on every other
odd-numbered line or some such algorithm. (In reality, encryption schemes are much more
complex!) The hash then becomes that object's "digital signature."
- Because the object and the password are combined to
create the signature, each object generates a unique signature and, if the object is
altered, its signature changes. A talented vandal can use the public key to generate a new
signature and the end user has no way of knowing that the package was altered from its
original state. This is where the magic comes in.
- Either the public key or the private key can be used
to determine the integrity of a file. Anyone can find out the public key (because its
embedded within the .SPC file). The private key, however, is known only to the vendor (and
perhaps the CA or its agent). When you receive a copy of suspicious software, check it
against its private key to determine whether it was altered.
For a walk through the steps of signing a control,
along with links to a certification authority, check out Microsofts Authenticode
site at http://www.microsoft.com/intdev/security/authcode/sixsteps.asp.
Many different government actions (such as the
Computer Decency Act and the Clipper chip in the United States, and Germany's temporary
ban on Compuserve) have tried, without success, to regulate violent or sexually oriented
content on the Internet. Each effort has failed, due to the distributed nature of the Net
and public outrage at anything that smacks of governmental censorship.
The World Wide Web Consortium has been working to
allow parental, employer and administrative control over this type of material.
Self-regulation is expected to prove much more successful than governmental action because
it empowers people closer to home to determine what material is or is not acceptable.
Internet Content Selection
The PICS standard is the result of several
conferences addressing the conflicting needs of censorship and free speech. By
implementing a standard system of rating content (much like in the film industry), content
developers can post labels on their network content, describing the level of risque[as]
material it contains.
This site is the home page for the development of the PICS standard. The World Wide Web
Consortium has taken on the effort of establishing a method for implementing rating
systems for Internet content that is more dynamic than the system used in theaters.
PICS is not attempting to establish how ratings are
assigned, but rather how rating systems are implemented.
This site is the home of the Recreational Standards Advisory Council. The RSAC provides a
PICS-compliant rating system and a Web interface for registering the content of Web sites
and individual Web pages.
Web site administrators can register the content of
their Web pages with an entity such as the RSAC. When you receive your ratings, they
should be placed within the <HEAD> container tag of an HTML document. An example of
this tag is as follows:
<META http-equiv="PICS-Label" content='
l gen true comment "RSACi North America Server"
r (n 0 s 0 v 0 l 0))'>
This example rates the URL
http://WWW.Domain.Net/User as a 0 (completely safe) for Nudity, Sex, Violence and
Language. It was registered in the name of User@Domain.Net, and is good from August 16,
1996 until January 1, 1997 between the hours of 8:15 AM and 5:00 PM. It's everything a
parent could ask for.
Internet Ratings API
Microsoft's Internet Ratings API exposes certain
features of the PICS standard to the programmer. This API is also part of Nashville
(Microsoft's code name for their Internet add-on pack).
With this API you can, of course, enable or disable
the ratings features. You can also check the authorized level of access enjoyed by the
current user. This access is defined by the PICS standard. If the user does not have a
level of access appropriate for the page, a Request Denied dialog is displayed.
Using this API, you can determine the ratings of a
site or compare the ratings on two different sites. In this way, you can assure a user (no
guarantees, though) that a site that reports a set of ratings has been verified by a
trusted 3rd party.
In this chapter you have learned about the processes
involved in downloading, verifying and installing ActiveX controls.
You have learned about two of the <OBJECT>
tag's parametersCode and CODETYPE, and how they can be used to identify the
location, version and machine type for a control. Files of several kinds can be used as
ActiveX controls, including portable executables, custom controls and cabinet archives.
You can add an .INF file to a cabinet or place it all by itself on a Web page to tell a
user's machine the where, how and what of installing ActiveX controls and their required
ActiveX uses an enhanced MIME type to identify the
type of computer, such as Mac, UNIX or Windows. This format allows a content provider to
enable a user to reap the benefits of an ActiveX Web site, no matter what type of computer
he prefers to use.
You are also familiar with many of the features of
ActiveX security. This set of APIs enables users of your control to rest assured that the
code they download from the Net is the same code that you posted.
ActiveX security relies on the use of X.509 and
PKCS#7 security certificates. These certificates are verified with a trusted authority,
such as a commercial or individual issuer. These security measures can reassure, but not
guarantee, a user that his copy of your code is intact. The only way to guarantee its
integrity is to process it against your top-secret private key. You can, but do not have
to, use the Base Security Layer SDK to enable these security features.
ActiveX has another type of security, based on the
PICS standard, to allow parents, employers and other authorities to censor access to
content they feel is not appropriate for their users. Using the Internet Ratings API, you
can add this level of security to your own standalone applications. Use the HTML
implementation of PICS to rate the content of your own Web pages.
- Q What other compression formats will work with
ActiveX besides Microsoft's cabinets?
- A Any compression method can be used to reduce
the size of a file. Cabinets are the only ones that can be used as true ActiveX controls.
This is because they are the only ones that are self-installing.
- Q. Does the ActiveX MIME type for identifying a
user's CPU and OS allow other platforms besides Mac and Windows?
- A Yes. There are tentative plans to extend
this to include UNIX and other systems, but not soon.
- Q. Is there an ActiveX security measure to protect
against viral infection?
- A No. ActiveX does not include antivirus
security. The public key encryption can help a user identify when a program has been
altered, but that's as far as it goes. To enable antivirus protection, you would need a
utility such as Norton Antivirus or Mcafee Virusscan.
- Q Does ActiveX allow a network administrator to
define what can be installed on the machines under his/her charge?
- A No. In a highly secure organization, such as
a bank or defense installation, firewalls and proxy servers can be set up to avoid many
threats. If users within the organization have access to the World Wide Web, the
administrator must train users about the threats and trust them to heed those warnings or
disallow Web access altogether. The whole point of ActiveX security is to allow the
client, rather than the server, to define what is or is not trusted.
- Q Is it possible for a malicious programmer to
create a fake X.509 certificate and distribute hazardous software that is signed with that
- A Yes, but it won't work. When an object is
marked as safe with an X.509 certificate, the client machine will verify the certificate
with the CA or LRA. Even if the x.509 certificate is perfect, if there is no confirmation
by a the third party trust-verification service, the object will not be treated as trusted
software. (The exception to this is when a user turns off his security features.)
Create an .INF file that performs the following
- Installs FooBar.OCX (Version 126.96.36.199) from the
current Web directory into the user's \Windows\System directory.
- Installs FooBar.DLL (Version 188.8.131.52) from the
current Web directory into the user's \Windows directory.
- What are the three phases in ActiveX component
- What container tag is used to identify an ActiveX
- What attribute of the tag from Question 2 is used to
identify the location and version of an ActiveX control?
- What attribute of the tag from Question 2 is used to
identify the MIME type of the control in Question 3?
- What three types of files are referred to as
- What file contains the information required to
install an ActiveX control and its related files?
- What code is used within the Setup Information file
to tell the system to load a control into the \Windows\System directory?
- What three parts of a Web page present opportunities
for security threats?
- Which SDK provides the tools for certifying a control
- What service provides the means for verifying that a
control signed with the SDK from Question 9 is safe for the user?
- What two issues are addressed by the Safety API for
determining the level of safety within an ActiveX control?
- What OLE property programmatically defines the level
of safety enjoyed by a control?
- What two facts about a vendor can be determined from
the signed control to validate its integrity.
- What level of security is obtained from the CA or the
- What two types of "passwords" are used in
public key encryption?
- What is the Internet standard for enabling security
measures dealing with the content of a site?
- What API is used to work with