how to fight a password cracker

[Madni]

Dear All,

Using pdflib library in C# I have created a pdf file which is
protected using owner password .Different options are disallowed like
print, copy contents etc. Things were working very fine untill i came
to know about some password crackers which could easily crack the
file , eliminating the password , thus making it possible for
operations like printing, copy etc .
The study showed that using user password as well will make the file
strong enough to be decrypted ,but "user password" is not a solution
in my case .

The code which actually creates a pdf file using pdflib is as under :

PDFLib obj = new PDFLib();
obj.begin_document(FileName, "masterpassword=23wdlm3ldjwld4w
permission={noprint}");

Now i wonder even that the file is encrypted using 128-bit
encryption , how a password cracker can retrieve that stored password
form the encrypted file .What operation is performed by the cracker to
remove the password and making the file accessible for all options .

Can any one please help me in this ....

Regards,
Madni

 

[Mark Rae]

Now i wonder even that the file is encrypted using 128-bit
encryption , how a password cracker can retrieve that stored password
form the encrypted file .What operation is performed by the cracker to
remove the password and making the file accessible for all options .

Can any one please help me in this ....

I'm afraid there's really nothing more to it than this:
http://www.google.co.uk/search?sour...GLG,GGLG:2006-28,GGLG:en&q=PDF+password+crack

 

[pfc_sadr]

uh I would use a real language like VB6 were you don't have to
obfuscate your source code

either that or

'dotnet is too verbose, your program won't work because it is
expecting more verbosity. try adding a bunch more code and see if
that helps'

 

[Ben Voigt]

PDFLib obj = new PDFLib();

obj.begin_document(FileName, "masterpassword=23wdlm3ldjwld4w
permission={noprint}");

Now i wonder even that the file is encrypted using 128-bit
encryption , how a password cracker can retrieve that stored password
form the encrypted file .What operation is performed by the cracker to
remove the password and making the file accessible for all options .

Well the password is obviously very easy to retrieve from the source code or
even compiled object code (language doesn't matter here), so I suppose your
users don't have the application, but you post the output on the network
somewhere for them.

The essential problem is that if they can view data they can always copy it.
This is a fundamental law that a lot of people don't seem to understand
(i.e. DRM systems for music and video). People keep trying, with platform
security, encryption all the way to the display, etc, but if I want a
printout, I can always use a hi-res camera or scanner and there's nothing
you can do.