PDF Password Cracking

    I sent an email to a vendor asking for a document and when the vendor replied to my email with the document attached, the document was password protected.  He said as much and he also said that I could probably crack it.  He is correct.  

    I've probably cracked a PDF once or twice.  I've probably also cracked a few ZIP files, RAR files, and various other files with passwords but I think you get the point.  Essentially, most of these types of files will all crack the same way -- John the Ripper.  

    There are a couple of John the Ripper versions but somewhere along the way, I discovered that the Jumbo John package is the one to use for cracking ZIPs and RAR files.  I don't know whether PDFs fall under that some umbrella but that's where I went.  

    To perform this little parlor trick, I went to one of the machines with the Jumbo package.  Prior to moving over to a terminal window for my little test case, I created a PDF document, password protected it, and then I moved it over to Kali.  

    Again, John versions vary so I just wanted to run this to see if I got a full hash.  There was a pdf2john.py version that didn't give me what I wanted.




    Looks good so now I re-run the command I redirect the output into a file titled:  "hash".  I then start cracking the hash with a small wordlist:

    perl /opt/john/run/pdf2john.pl ./topsecret.pdf > hash

    /opt/john/run/john hash --wordlist=/usr/share/wordlists/top500.txt




    Not that I've created the most secure password, this was more of just proving a point.  So now we have the password -- "s3cret", we're going to attempt to open the document with our newly acquired password:





    It accepts our password:




    And now you can see what I truly think are top secret documents.  Btw, this recipe was delicious!  

    The real point of this exercise is to show you that this false sense of security is just that.  A more complex password would have stopped my wordlist brute force but there are other methods for countering that problem as well.  


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