How to crack / recover an Adobe PDF password using pdfcrack for Linux.

From time to time I am asked to break a password on an Adobe PDF file. This mostly comes up when the user who created the pdf can’t remember what their own password is. As annoying as that is, actually recovering the password is simple using pdfcrack.

PDFCrack is a GNU/Linux application (or any other POSIX-compatible system) tool for recovering passwords and content from PDF-files. It is small, command line driven, and without external dependencies. PDFCrack is released under GPL.

Install pdfcrack on Ubuntu by typing:

sudo aptitude install pdfcrack


Run a quick benchmark by entering the following at the command line:

pdfcrack -b


Results:

Benchmark: Average Speed (calls / second):
MD5: 2616026.7
MD5_50 (fast): 146928.3
MD5_50 (slow): 107780.3

RC4 (40, static): 863985.7
RC4 (40, no check): 864661.2
RC4 (128, no check): 802203.0

Benchmark: Average Speed (passwords / second):
PDF (40, user): 653588.2
PDF (40, owner): 322317.1
PDF (40, owner, fast): 714278.6

PDF (128, user): 30861.1
PDF (128, owner): 14687.8
PDF (128, owner, fast): 30861.1

Use pdfcrack to crack an encrypted pdf-file by typing:

pdfcrack test.pdf