nbdkit-luks-filter1

Usage

Overview

"nbdkit-luks-filter" is a filter for nbdkit(1) which transparently opens a LUKS-encrypted disk image. LUKS ("Linux Unified Key Setup") is the Full Disk Encryption (FDE) system commonly used by Linux systems. This filter is compatible with LUKSv1 as implemented by the Linux kernel (dm_crypt), and by qemu.

You can place this filter on top of nbdkit-file-plugin(1) to decrypt a local file:

 nbdkit file encrypted-disk.img --filter=luks passphrase=+/tmp/secret

If LUKS is present inside a partition in the disk image then you will have to combine this filter with nbdkit-partition-filter(1). The order of the filters is important:

 nbdkit file encrypted-disk.img \
             --filter=luks passphrase=+/tmp/secret \
             --filter=partition partition=1

This filter also works on top of other plugins such as nbdkit-curl-plugin(1):

 nbdkit curl https://example.com/encrypted-disk.img \
             --filter=luks passphrase=+/tmp/secret

The web server sees only the encrypted data. Without knowing the passphrase, the web server cannot access the decrypted disk. Only encrypted data is sent over the HTTP connection. nbdkit itself will serve unencrypted disk data over the NBD connection (if this is a problem see nbdkit-tls(1), or use a Unix domain socket -U).

The passphrase can be stored in a file (as shown), passed directly on the command line (insecure), entered interactively, or passed to nbdkit over a file descriptor.

This filter can read and write LUKSv1. It cannot create disks, change passphrases, add keyslots, etc. To do that, you can use ordinary Linux tools like cryptsetup(8). Note you must force LUKSv1 (eg. using cryptsetup --type luks1). qemu-img(1) can also create compatible disk images:

 qemu-img create -f luks \
                 --object secret,data=SECRET,id=sec0 \
                 -o key-secret=sec0 \
                 encrypted-disk.img 1G

Parameters

passphrase=SECRET

Use the secret passphrase when decrypting the disk.

Note that passing this on the command line is not secure on shared machines.

passphrase=-

Ask for the passphrase (interactively) when nbdkit starts up.

passphrase=+FILENAME

Read the passphrase from the named file. This is a secure method to supply a passphrase, as long as you set the permissions on the file appropriately.

passphrase=-FD

Read the passphrase from file descriptor number "FD", inherited from the parent process when nbdkit starts up. This is also a secure method to supply a passphrase.

Files

$filterdir/nbdkit-luks-filter.so

The plugin.

Use "nbdkit --dump-config" to find the location of $filterdir.

Version

"nbdkit-luks-filter" first appeared in nbdkit 1.32.