# can pdfcrack software crack a 128 bit encrypted pdf file

One day ago,i downloaded a pdf that requires password then i search a software to decrypt the password that's s/w called pdfcrack Then i install pdfcrack and run a cmd in terminal pdfcrack -f encrypted.pdf then it shows a some of sentences like that "Average Speed:13343.1 w/s. Current Word: 'txgeg'. " My doubt is when it completes in days or months or years

• Depends on the password. If it's a good password it should never finish. – CodesInChaos Apr 17 '16 at 10:37
• @CodesInChaos "never" is a bit too strong here. Let's formulate it more accurately: Chances are (if the password is any good or at least somewhat creative) that you won't be alive any longer to witness the end of the operation. – SEJPM Apr 17 '16 at 13:00
• @SEJPM unless he is considering that the machine will die before the process has finished... :D – Hilder Vítor Lima Pereira Apr 19 '16 at 13:10

Since it uses 128-bit encryption, there are at most $2^{128}$ keys. So if the password is complex enough, you will need on average $2^{127}$ tries. Which is about $1.28×10³⁴$ seconds, or so long that yon can't live that long.