![]() I’m storing the output in file “encryption_test – CONFIDENTIAL.hash”.Īnd now we can finally use hashcat. Let’s extract field 2 (you can use awk instead of csv-cut.py): ![]() For hashcat, just the hash is needed (field 2), and no other fields. This format is suitable for John the Ripper, but not for hashcat. However, I use a patched version of pdf2john.py that properly handles default 40-bit keys. For example, it would not properly generate a hash for 40-bit keys when the /Length name was not specified (like is the case here). Remark that John the Ripper (Jumbo version) is now using (a Perl program), because there were some issues with the Python program (pdf2john.py). I’ve written some blog posts about decrypting PDFs, but because we need to perform a brute-force attack here (it’s a short random password), this time I’m going to use hashcat to crack the password.įirst we need to extract the hash to crack from the PDF. This output (invalid password) tells us the PDF document is encrypted with a user password. QPDF can be used to determine if the PDF is protected with a user password or an owner password: PDFs encrypted with a owner password can be opened without providing a password, but some restrictions will apply (for example, printing could be disabled). PDFs encrypted with a user password can only be opened by providing this password. PDFs can be encrypted for confidentiality (requiring a so-called user password /U) or for DRM (using a so-called owner password /O). This encryption method uses a 40-bit key (usually indicated by a dictionary entry: /Length 40, but this is missing here). Pdfid.py confirms the PDF is encrypted (name /Encrypt):įrom this I can conclude that the standard encryption filter was used. So first, let’s check out how the PDF is encrypted. Here is how I decrypted the “easy” PDF (encryption_test).įrom John’s blog post, I know the password is random and short. In this series of blog posts, I’ll explain how I decrypted the encrypted PDFs shared by John August (John wanted to know how easy it is to crack encrypted PDFs, and started a challenge).
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