How can I use TrueCrypt under windows 8.1?

The last time they even put out an update was almost 2 years ago. I really don't think there is even any development on it anymore. According to their site Windows 8 is not supported at all. Here is the supported OSs page.

http://www.truecrypt.org/docs/supported-operating-systems

I am currently using Bitlocker for one encrypted drive. Bitlocker is native to Windows 8 now. You would be better off either getting a different encryption suite or use Bitlocker.

Although TrueCrypt have announced their intentions to support Windows 8 and UEFI, their last version still dates from 2012.

As far as I can see, your options today are :

1. Partition your disk into two parts, Windows and TrueCrypt.
   If you are worried about unauthorized boot of your computer, put a password on the BIOS.
2. Use BitLocker instead of TrueCrypt, if you have the right Windows version.
3. Convert your Windows disk from GPT to MBR, so it doesn't use UEFI, and turn off Secure Boot in the BIOS. This will delete all partitions and recreate an empty MBR disk to which you can reimage the Windows partition. Take care that the Windows partition will have the same partition number as before (even if you need to add dummy partitions in front of it).

I suggest that you first take an image backup of your entire hard disk and ensure that you have a bootable CD or USB that can restore it in case of catastrophe. Do not use Windows Backup. My favorite tool is the free AOMEI Backupper.

There are several methods that you can use to convert GPT disk to MBR.

1. Use EaseUS Partition Master
2. Use the diskpart command
3. Use Windows Disk Management

The second method (for which I take no responsibility) requires booting the Windows DVD without UEFI, going to the repair options / command prompt, and then entering :

diskpart
list disk
select disk 0
clean
convert mbr
create partition primary
select partition 1
format fs=ntfs quick

For the third method, if you can extract the hard disk from your computer and put it on another computer, even inside an external enclosure, then you could use Windows Disk Management to do the conversion.

For more information see the article How to Convert GPT Disk to MBR Disk.

You can do it, but it depends a bit on your hardware and your expectations of a properly functioning Windows 8.1 + TrueCrypt installation. TC still works for encrypted containers in W81, but since it relies on having an MBR partitioned disk and integrated bootloaders, for full disk encryption, it will not work in a sensible way, since W81 need GPT formatted disks etc. So you have to get more sensible, by just using containers, or better, just install W7+TC in a VM on top of W81. There's some various good TC advice on Reddit and DSLReports.

(It is highly unlikely we'll see any more TC updates after the Snowden incident. It's simply cheaper for the gov't to buy out the TC people and shut down the business, than chasing leakers all over the planet.)

PS. To use BitLocker, you'll need Windows 8.1 Pro or Enterprise editions. But I wouldn't use it after reading this and this.

I just successfully finished system disk encryption using the current stable version of TrueCrypt (7.1a) on Windows 8.1. I did it without any problems.

1. The bottom line is that Windows MUST BE installed in the "Legacy" mode, in other words, Windows must be installed on the hard disk with the "classical" (MSDOS type) MBR instead of the newer GPT.

   You can get it when you start your Windows 8.1 Installer in the "Legacy" mode instead of the "UEFI" mode. This is done in the BIOS options when starting the computer and pressing DEL, F2 or similar (depends on the motherboard manufacturer) and choosing "Boot options" or similar. If your hard drive has a boot record of GPT type, you must delete it and replace with the classical MBR. This can be done, for example, with free software called "Gparted".

2. Another key issue is that Windows MUST BE installed only on ONE partition instead of TWO partitions.

   This can be achieved by creating at the VERY BEGINNING OF THE DRIVE a single NTFS partition of the appropriate size by using external software (for example, "Gparted") and forming a second partition which occupies the entire remaining disk space formatted as ext3/ext4, or any other type that Windows does not recognize - after the installation is completed you should remove this partition. Then you must start the computer from the Windows installation disc in the "Legacy" mode and instruct the installer to install the system on the first partition.