# How much time does AES decryption take?

I am attempting to decrypt a 90 GB file that is encrypted using AES-256. I have the password. How long should this take to complete? I've had the process running for over 3 days with no progress.

• Not that long. Something's clearly wrong with the software you're using. Unfortunately, even if you told us which software it is, this is really an issue to take up with their tech support, not here. – Ilmari Karonen Aug 21 '18 at 14:20
• on my computer (10 years old) that would take about 45 minutes, since it needs to read and write 90GB to disk in a sequential manner on a 10K RPM hard disk – Richie Frame Aug 21 '18 at 19:57
• ry without a virus scanner. You may have had the file locked and the system hang up on you. Would not be the first time. This is especially tricky if the output file is an archive such as a .zip file. – Maarten Bodewes Aug 21 '18 at 23:14
• If it is decrypting you would expect a core on your CPU to max out. – Maarten Bodewes Aug 21 '18 at 23:15

I am attempting to decrypt a 90 GB file that is encrypted using 256 AES. [...] How long should this take to complete?

If the AES implementation and the program doing the decryption are any good this is only bound by the speed of your drive, if your processor is newer than from about 2012. So for an SSD, you should be able to hit 200MB/s and with an HDD 50MB/s with little problems, if the program doesn't have some horrendous overhead and utilizes a sane implementation and with an older / weaker processor, you should still be able to saturate the HDD and run the SSD at about half speed.

Note however that certain platforms, e.g. standard python don't actually compile to machine code and thus are extremely slow, ie in a measurement I did recently I hit about 1MB/s with the interpreter. But even then it should "only" take you 25 hours. So chances are the program you are using is extremely poorly implemented and you should strongly consider using an alternative if you can.

• I am using the current version of GPG and a computer that is less than 2 years old with an intel i7 processor. My suspicion is that I was sent corrupted data. I just want to rule out, as best I can, that I'm not giving the computer enough time to complete the decryption. Thank you for your help. – Jon Aug 21 '18 at 14:25
• @Jon: Even with corrupted data, the software should've figured out that it was wrong (or possibly not figured it out, and given you 90 GB of garbage) much sooner. I still think this must be a bug. (Or possibly user error; have you checked whether you can encrypt your own (smaller) file and decrypt it again using the same tools?) – Ilmari Karonen Aug 21 '18 at 22:46