GuaPDF (Guaranteed PDF Decrypter)

1. What PDF files are not supported?

GuaPDF doesn't support:

• User-password protected files with 128 or 256-bit encryption. Guaranteed decryption is impossible for such a files. Please look at Parallel Password Recovery for PDF files
• Files with non-standard encryption, such as e-books etc.

2. I have tried demo version but the decrypted file contains only few pages and/or produces strange error messages...

Demo version can correctly decrypt only few streams and doesn't decrypt strings (look at PDF specification if you don't know what does it mean). All the rest streams remain unencrypted. It means only few (or zero pages) will be visible in the decrypted document. It may also produce some error messages. Don't worry, the full version will correctly decrypt your document.

3. How can I test if your program is working?

To test restrictions removal, run GuaPDF on RESTRICT.PDF file in the archive. To test password cracking and decryption, run GuaPDF on ENCRYPT.PDF file in the archive and wait until it finishes testing key 0. (The user password for last file is 'gird', the owner password for both files is 'owner').

4. What are the differences between freeware and commercial version?

a) Demo version is limited to decrypt only few streams - it means, only small files can be processed correctly
b) Distributed mechanism
c) Starting and ending key arguments, Restart option
d) Support

5. Can you explain the differences between commercial versions?

Restrictions remover version is designed to unset operation restrictions only. Other versions can also do that, and can be used for decrypting documents with user password. They differ only by available clients number. If you are not sure what version to buy, run demo version on your file and look what it says.

6. How to use the program in batch mode to process a lot of files?

I recommend to use the command-line version of GuaPDF. All the customers of GUI version may receive it for free. But the GUI version also supports command-line parameters. For all file in one folder, use FOR command, like:

for %i in (*.pdf) do guapdf /y %i

or, in .BAT file:

for %%i in (*.pdf) do guapdf /y %%i

7. Your program produces a lot of warnings: "String truncated in line XXX". What do they mean?

From 2.0 version, this occurs only and rarely for PDF 1.5+ files and will be possibly fixed in newer versions.

When decrypting, some strings need to be truncated. For majority of PDF documents, these truncations don't affect the resulting file in any way. If your document is affected, mail me

8. Will the signature on signed PDF file be valid after decryption/removing restriction?

Of course not, because the file will be changed.

9.I can't save data in forms in Acrobat Reader after decryption.

If you got a messsage "You cannot save data typed into this form" after decryption, then you need to enable Adobe LiveCycle Reader Extensions. To do it, you may use Acrobat Professional, go to Advanced->Extend Features in Adobe Reader and save the file.

10.After decryption there is no security, but I got the message " This PDF form restricts some operations"

Yes, some PDF forms may restrict some operations by themselves. To edit these forms, you need Adobe LiveCycle. With Acrobat Professional, go to Forms->Edit Form in Designer.

11. How to interrupt and continue searching?

The program can be interrupted by choosing Close or Exit from the File menu  and continued by running with the same options (no need to change the keyspace range - it will be picked up automatically).
(*) Continuing is impossible in freeware version, it will start from key 0.

12. What do the values in .key file mean?

First 16 bytes are special. The byte with n offset means the state of (n-16) key and may be one of 3 values: 0 - key is not tested yet, 1 - key was tested and is not right, 2 - key is testing now (or may be interrupted key).So, if the test of a given keyspace is completed, and there are still some values (in this keyspace) which are not equal to 1, then there must be a bug in the program. Those keys, which have not been tested, can be tested by simply running the program on this keyspace again with /r option.

13. How to use power of 2 (4) cores?

Using of many cores make sense only when searching for open password (40-bit key). To use 2 (4) cores, just run two (four) instances of GuaPDF Local version with the same parameters.

14. I've got quad-core computer, but key testing time is extremely large.

a) Make sure that other CPU hungry programs (including 3D-screensavers) are not running simultaneously. Also, incorrect CPU options may significantly decrease the speed of the program. Check the options and verify that a correct CPU type is chosen.

b) Give 100% CPU time to the program. Easiest way to do it is change programs priority in the Options menu. c)To use power of 4 cores, you should get distributed (20-clients) version, it will find the key faster, because local version supports only 2 cores.

15. I try to put 'gird' password on my .pdf file, and your program can't decrypt it within 0 key attempt.

Sure, ENCRYPT.PDF is an especially constructed example, and you have no chances to make such (fast breakable) file using standard PDF creating software. See q. 20.

16. The full keyspace has been tested, no key found.

Check for interrupted keys in .key file (see q.11) or just simply run program again with Restart option. If it is still fails, your PDF file is seriously corrupted or it's a bug.

17. Your program found a key, successfully decrypted a file and I still can not open it...

First, don't despair. The found key is correct and your file can be decrypted. Just contact me, and I'll fix this bug, and you won't need to test the keys again.

18. Is it possible to speed up/port your program to the another architecture?

The GuaPDF engine is portable, so the UNIX version can be compiled (Linux, Solaris and Mac versions are already available). The optimized kernel crypto functions also can be easily added. So, if you are interested in, please contact.

19. Program displays "no more clients (N) allowed in this keyspace", although less than N clients are running.

You've interrupted some of the clients incorrectly. Stop other clients and use Restart option.

20a. Freeware version found the key, but couldn't (correctly) decrypt the file. Is there the way for not searching for the key again?

20b. Freeware version had tested some (a lot of) keys when I decided to buy commercial version. Is there the way for not testing them again?

Sure, just run commercial version with appropriate Keys from... parameter.

21. I'm sure all of my files are encrypted with the same password, and I successfully decrypted one of them. Can I decrypt others without running GuaPDF on all files?

Files with the same password DON'T have the same key, because it depends on file ID etc. and there is no way to decrypt other files if you even know the key of one of them. I think, however, that it is possible to write PASSWORD recovering utility from given key and .pdf file.

22. My file is confidential and I don't want it to remain in the shared directory. What shall I do?

You can remove your file after the key testing begins and copy it back when the prompt for decryption will appear.

23. The key has been found on one of the clients while first client was stopped. How to decrypt file in this situation?

Just start first client with First mode option.

24. I've got "Permission denied" error message:

Make sure your file is not Read-Only nor used by another program.

25. Should I start two GuaPDF copies on my HyperThreading processor?

Curiously enough, but on some modern Pentium 4 Prescott it may help, on other (older) P4 it has no sence.

26.Could you explain more about first client mode?

"First client" only means that the decryption will be perfomed on this client and doesn't have any other peculiarities. It makes no harm if several "first clients" are running or none of them are running.

27. What I need to use GPU acceleration?

You need modern NVIDIA video card (from 8xxx serie) and the latest CUDA-capable drivers.

28.How can I achive maximal performance using CPU and GPU together?

On some systems you'll get the maximal speed if you remain one free CPU core for each CUDA client running. So, if you got 4-core processor and 2 GPU cards, you should run 2 CPU clients and 2 GPU ones. But, on some systems you may use all cores and all GPUs for key testing. You should make an experiment to check out the best running clients number.