Password Recover

Do you know anything else about the password. For example the first few characters? Or if it is upper / lower case? Are you sure it is exactly 10 characters?

Do you have access to the machine it came from? You can make a word dictionary from the hard disk contents and then try the dictionary against the document? This is much more efficient than a random attack.

I assume the PDF isn't using the old 40bit PDF encryption. As this shouldn't take 3 days with any software to crack.

10 mixed upper and lower case characters gives 144,555,105,949,057,024 permutations. With 256bit AES encryption you should be able to test around 5 million passwords a second on a single machine.

Which means 916 years of processing time, if I have my maths right. Of course you might get lucky and get it in a few days, but the odds are low.

Which means 916 years of processing time, if I have my maths right. Of course you might get lucky and get it in a few days, but the odds are low.

Dang, if only you were a Time Lord…

Dang, if only you were a Time Lord…

Yes, could go back in time and look over the shoulder of the PDF author to see what password they entered -)

Hi,

This is a project assignment that I have received from universities and reportedly they have encrypted PDF file with an AES 128 bit encryption algorithm and a password of 10 characters.
That's all we knew o with the information we will decrypt the file o access the information in the file.

some suggestions for solutions?
thanks

Do you know anything else about the password. For example the first few characters? Or if it is upper / lower case? Are you sure it is exactly 10 characters?

Do you have access to the machine it came from? You can make a word dictionary from the hard disk contents and then try the dictionary against the document? This is much more efficient than a random attack.

I assume the PDF isn't using the old 40bit PDF encryption. As this shouldn't take 3 days with any software to crack.

10 mixed upper and lower case characters gives 144,555,105,949,057,024 permutations. With 256bit AES encryption you should be able to test around 5 million passwords a second on a single machine.

Which means 916 years of processing time, if I have my maths right. Of course you might get lucky and get it in a few days, but the odds are low.

A bit of The Art of War thinking what kind of word-list did you gather to generate a custom dictionary for your attack?

I have not been tested against a specific password list I have selected a combination of all the opportunities thus A-Z, a-z, 0-9 and also special characters, but now I have uploaded a couple of other password lists from this page;
http//www.skullsecurity.org/wiki/index.php/Passwords
what do you think?

A bit of The Art of War thinking what kind of word-list did you gather to generate a custom dictionary for your attack?

You could also try just guessing it.
Is the name of the University 10 characters long?
Is the file name 10 characters long?
Is the meta data in the PDF also encrypted? Maybe there is a hint in the file itself.

Greetings,

Are you supposed to be using outside sources to solve your homework assignment? Yes, this is a useful discussion, but it also appears that it might be an inappropriate one.

-David

Hi David
I believe that the purpose of the project assignment is not the answer however, how to solve the task.
I want to learn about how you (experts) think when you are going to solve that kind of problems becouse there are several ways / methods to solve the problems and it is not something you can read on the books.

Sincerely,
shgh

Greetings,

Are you supposed to be using outside sources to solve your homework assignment? Yes, this is a useful discussion, but it also appears that it might be an inappropriate one.

-David