# 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

I thought I share my real life experience with decrypting AES-256

When i encrypt my computers main harddrive that run windows 10 ( its a 256gb m2 drive ) then decrypting the drive entirely using the fantastic software named Veracrypt ( formely known as truecrypt ) then it take about 5 minutes to decrypt and remove aes-256 and the decryption from the harddisk.

If i decrypt an 256 SSD it take a little longer. If i decrypt from dos/command prompt ( outside windows ) then it take like 20 minutes i think.

Externaly on my network I have a NAS server that is 6TB large, and it have a much slower processor and run on 3x2tb 7200rpm mechanical harddrives combined together in RAID 0. It take 4-6 days to create a encrypted 6tb file container.

To people who do not know veracrypt/truecrypt. Then it "pre" encrypt a container where you can store data inside. So it is only 1 time you encrypt the file container or harddisk, and then you just enter your code and your data is avaliable 2 seconds later. If you encrypt the harddisk with windows 10 then you see a black screen with text asking for your password when you boot your computer. ( tip in rare cases if your computer break, insert rescue veracrypt disk and decrypt your pc to be able to repair/install update in windows 10 ). tip 2.. Be aware that encrypting your harddisk will reduce performance about 25% however if you use ssd or m2 drive you will not notise the difference on ordinary usage.