Bitlocker disk encryption -
BitLocker Disk Encryption (BDE) is Full Volume Encryption solution by Microsoft first included with the Enterprise and Ultimate editions of Windows Vista. It is also present in Windows 7 and later version along with a system for encrypting removable storage media devices, like USB, which is called BitLocker To Go. Unlike previous versions of BitLocker, BitLocker To Go allows the user to protect volumes with a password or smart card.
BitLocker
BitLocker encrypts data with either 128-bit or 256-bit AES and optionally using a diffuser algorithm called Elephant. The key used to do the encryption, the Full Volume Encryption Key (FVEK) and/or TWEAK key, is stored in the BitLocker metadata on the protected volume. The FVEK and/or TWEAK keys are encrypted using another key, namely the Volume Master Key (VMK). Several copies of the VMK are also stored in the metadata. Each copy of the VMK is encrypted using another key, also know as key-protector key. Some of the key-protectors are:
TPM (Trusted Platform Module)
Smart card
recovery password
start-up key
clear key; this key-protector provides no protection
user password
BitLocker has support for partial encrypted volumes.
BitLocker To Go
Volumes encrypted with BitLocker To Go will have a hybrid encrypted volume, meaning that part of the volume is unencrypted and contains applications to unlock the volume and the other part of the volume is encrypted. The "discovery drive" volume contains BitLocker To Go Reader to read from encrypted volumes on versions of Microsoft Windows without BitLocker support.
How to detect
Volumes encrypted with BitLocker will have a different signature than the standard NTFS header.
A BitLocker encrypted volume starts with the "-FVE-FS-" signature.
A hexdump of the start of the volume should look similar to:
00000000 eb 58 90 2d 46 56 45 2d 46 53 2d 00 02 08 00 00 |.X.-FVE-FS-.....| 00000010 00 00 00 00 00 f8 00 00 3f 00 ff 00 00 00 00 00 |........?.......| 00000020 00 00 00 00 e0 1f 00 00 00 00 00 00 00 00 00 00 |................| 00000030 01 00 06 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 00000040 80 00 29 00 00 00 00 4e 4f 20 4e 41 4d 45 20 20 |..)....NO NAME | 00000050 20 20 46 41 54 33 32 20 20 20 33 c9 8e d1 bc f4 | FAT32 3.....| 
These volumes can also be identified by a GUID:
for BitLocker: 4967d63b-2e29-4ad8-8399-f6a339e3d00
for BitLocker ToGo: 4967d63b-2e29-4ad8-8399-f6a339e3d01
Which in a hexdump of the start of the volume should look similar to:
000000a0 3b d6 67 49 29 2e d8 4a 83 99 f6 a3 39 e3 d0 01 |;.gI)..J....9...| 
manage-bde
To view the BitLocker Drive Encryption (BDE) status on a running Windows system:
manage-bde.exe -status 
To obtain the recovery password for volume C:
manage-bde.exe -protectors -get C: -Type recoverypassword 
Or just obtain the all “protectors” for volume C:
manage-bde.exe -protectors -get C: 
manage-bdg.wsf
You can unlock a drive with the cscript command, leaving the master key in the clear by using these commands:
cscript manage-bdg.wsf unlock c: cscript manage-bdg.wsf autounlock enable c: 
Changes in Bitlocker for Windows 10
As of the fall of 2015, Microsoft introduced a new mode in Bitlocker on Windows 10, XTS-AES. Volumes encrypted in this manner are not backwards compatible with previous versions of Windows/Bitlocker and can only be opened on Windows 10 systems and later.
See Also
BitLocker: How to image
External Links
Wikipedia entry on BitLocker
Accessing Bitlocker volumes from Linux, by Nitin Kumar and Vipin Kumar, 2008
Implementing BitLocker for Forensic Analysis, Digital Investigation, by Jesse D. Kornblum, 2009
BitLocker Drive Encryption (BDE) format specification, by the libbde project, March 2011
Microsoft Technical Overview
An Introduction to Security in Windows 7
Microsoft Description of the Encryption Algorithm
What's New in BitLocker in Windows 8
Windows 10 Version 1511 gets new XTS-AES BitLocker encryption algorithm
What's new in BitLocker Windows 10
Tools
dislocker
libbde
M3 Bitlocker Loader for Mac
M3 Bitlocker Recovery
Manage-bde.exe