Hello Tom,
Thank you for posting your query on Microsoft Community.
As per description, you like to know about the encryption using Bit locker on windows 8.1.
You can use BitLocker Drive Encryption to help protect your files on an entire drive. BitLocker can help block hackers from accessing the system files they rely on to discover your password, or from accessing your drive by physically removing it from your PC and installing it in a different one.
I would suggest you to follow the article below and check if that helps.
You can refer the link below and check
http://windows.microsoft.com/en-us/windows-8/bitlocker-drive-encryption
Additionally you can refer to the link below.
BitLocker Drive Encryption Overview.
https://technet.microsoft.com/en-us/library/cc732774.aspx?f=255&MSPPError=-2147217396
****Disclaimer: Modifying BIOS/ complementary metal oxide semiconductor (CMOS) settings incorrectly can cause serious problems that may prevent your computer from booting properly. Microsoft cannot guarantee that any problems resulting from the configuring of BIOS/CMOS settings can be solved. Modifications of the settings are at your own risk.
Hope the information helps. Let us know if you need further assistance with Windows, we’ll be glad to assist you.
Thank you