Regaining Access to a Fairly Old Encrypted PDF?

May 16, 2008 8:57 AM

Is there a way that I can access some very old PDF files that are encrypted with a password I cannot remember any longer? I have a system running Mac OS X (Leopard), and I do need to do the decryption myself.

These files are indeed my property and owned by me, so this question isn't the setup for a crack.

I can't seem to locate the originator of these PDFs on the Internet any longer (unsurprising as these files are very old), so obtaining the password from them isn't an option. And the files are old enough that if I did keep the password anywhere, it's utterly gone now.

And it's very possible the files may have content that is somewhat private in nature, which rules out the possibility of having another party do the decryption.

Although it's not the very top of the line, I do have a Core Duo 2 Intel iMac with two gig of RAM, so hopefully that's enough machine to adequately do any number-crunching necessary.

posted by WCityMike to computers & internet (12 comments total)

pdfcrack
posted by jozxyqk at 9:02 AM on May 16

Google is your friend: pdf password cracker. I see Elcomsoft in the results, and I remember there was a high profile case a few years ago where Adobe went after their top programmer for breaking the copy protection on eBooks.
posted by zippy at 9:06 AM on May 16

> Google is your friend

Google is not my friend when the search you recommend returns Windows applications that crack PDF files. As the question notes, I own a Mac.
posted by WCityMike at 9:11 AM on May 16

> pdfcrack

Thanks. That looks promising; I look forward to getting home and giving it a try.
posted by WCityMike at 9:12 AM on May 16

You can try opening the file in ColorSync and saving as another file. The resulting PDF will not be password protected but some layouts might get borked.
posted by jamaro at 9:13 AM on May 16 [1 favorite]

> You can try opening the file in ColorSync and saving as another file. The resulting PDF will not be password protected but some layouts might get borked.

I know that that technique used to work, but I thought I remembered hearing it was closed. Does that technique still work in Leopard? And if so, which ColorSync application do I open it in?
posted by WCityMike at 9:28 AM on May 16

I'm still using 10.4.x, didn't know it might have been 'fixed' in Leopard, that would be a bummer since I often use it on PDFs sent by forgetful clients. ColorSync Utility.app is the one to pick via control+click Open With.
posted by jamaro at 9:37 AM on May 16

Thanks, Jamaro. I will give it a try with ColorSync Utility when I get home before I try pdfcrack, and see if the technique still works.
posted by WCityMike at 9:40 AM on May 16

This has worked famously for me on multiple occasions, but it is a Windows app.
posted by Samizdata at 1:13 PM on May 16

Just as an update, Leopard's ColorSync Utility didn't make the file viewable. I've had pdfcrack cranking away 24/7 for a number of days now — it is essentially doing a brute force attack on the files, which is time- and CPU-consuming but, if I'm not mistaken, fairly likely to work. One thing I'm impressed with is that if you Ctrl-C out of pdfcrack, it notices that you're doing that and saves its place, so that you can resume from the same spot later without losing prior work. Nice. If I finally get into the files, I'll post a heads-up.
posted by WCityMike at 8:31 AM on May 19

May 21st, and it's still cranking away, although it's scaled itself up to seven-letter combinations now.
posted by WCityMike at 9:26 PM on May 21

May 24th, and it just cracked it. Although I have heard anecdotally that with English-word passwords, it cracks it in under five minutes. This was a random string of seven letters.

Of course, now that I know that the PDF author uses seven-letter passwords, I can tell it to start with seven-letter passwords, which should hopefully cut down some of the time for the remaining two.
posted by WCityMike at 7:56 AM on May 24 [1 favorite]