emerge --ask sys-fs/dislocker
A note on fstab
BitLocker partitions can be mount-ed using the /etc/fstab file and dislocker's long options. The line below is an example line, which has to be adapted to each case:
/dev/sda2 /mnt/dislocker fuse.dislocker user-password=blah,nofail 0 0
With the sample /etc/fstab as above, make sure the two mount points /mnt/dislocker and /mnt/clear exist. Then:
mount -o loop /mnt/dislocker/dislocker-file /mnt/clear
The first mount creates the file /mnt/dislocker/dislocker-file, which is the raw unencrypted NTFS from inside the BitLocker partition. The second command mounts that NTFS partition onto /mnt/clear.