Introduction

In this post I’ll show you how to unlock LUKS disk (with root partition / file system) using the Nitrokey Pro 2 Password Safe.

Warning

This guide is only tested on my Gentoo box, SO BE CAREFUL, YOU CAN MAKE YOUR GENTOO UNBOOTABLE.

Install nitrokey application

First install nitro-app

# emerge --ask app-crypt/nitrokey-app

now, configure the Nitrokey Pro 2 following the official documentation, changing the pin and the admin pin, and creating, under the Password Safe tab a new entry with LUKS Slot name Nitrokey app Copy the password, because we need to add it to LUKS

Add new passphrase to LUKS

Just add the new passphrase to LUKS (copied from Nitrokey App), for me the LUKS partition is /dev/sda2, but verify on your system

# cryptsetup luksAddKey /dev/sdaX
Enter any existing passphrase:     <-- insert the current passphrase
Enter new passphrase for key slot: <-- insert the new generated passphrase
Verify passphrase:                 <-- insert the new generated passphrase

now you can see two key slot for your device

# cryptsetup luksDump /dev/sda2 
LUKS header information for /dev/sda2

Version:        1
Cipher name:    aes
Cipher mode:    xts-plain64:sha512
Hash spec:      sha256
Payload offset: 4096
MK bits:        512
MK digest:      5a 08 78 7b 00 fb 82 0a e1 4e 73 e8 fc 12 6e ed d5 a3 82 ab 
MK salt:        21 8b 08 02 8f 8a 17 42 7a 85 bc 6c af cd 6c fb 
                82 27 0e 1e 24 27 1c 5f 7f 47 33 d7 03 e9 c3 a8 
MK iterations:  164000
UUID:           85558b31-7351-4c5f-b283-2a58d4cd7b71

Key Slot 0: ENABLED
        Iterations:             1311138
        Salt:                   fa 5d 2b f5 1b 46 34 d0 61 dd 18 35 c3 00 5f fa 
                                1c 23 5b 41 d1 6a 6e df e1 43 b4 8f e6 e2 a7 ad 
        Key material offset:    8
        AF stripes:             4000
Key Slot 1: ENABLED
        Iterations:             1344328
        Salt:                   10 cb 0a 59 60 15 85 cf 3c 00 d5 92 41 75 36 ba 
                                62 aa b0 0f a3 00 d2 a1 7b aa 98 91 d5 73 57 ca 
        Key material offset:    512
        AF stripes:             4000
Key Slot 2: DISABLED
Key Slot 3: DISABLED
Key Slot 4: DISABLED
Key Slot 5: DISABLED
Key Slot 6: DISABLED
Key Slot 7: DISABLED

Configure initramfs to use nitroluks

We’ll use the C++ source code kept from Nitroluks, who is a simple iterator from Nitrokey Pro 2 Password Safe slots, simple but very useful.

Configure genkernel-next to inject an overlay

Edit /etc/genkernel.conf with the following parameter

INITRAMFS_OVERLAY="/etc/kernels/nitro"

Create the initramfs overlay

Create the postbuild.d direcotry

# mkdir -p /etc/kernels/postbuild.d

Create a new script 10-nitrokey.sh inside the postbuild.d directory

# touch /etc/kernels/postbuild.d/10-nitrokey.sh
# chmod 0754 /etc/kernels/postbuild.d/10-nitrokey.sh

Put this content inside the 10-nitrokey.sh script file or download from here

#!/usr/bin/env bash
#
source /etc/genkernel.conf
rm -rf ${INITRAMFS_OVERLAY}
mkdir -p ${INITRAMFS_OVERLAY}/{usr/lib64,usr/bin,lib64,bin,etc/initrd.d}
NITROLUKS="https://github.com/artosan/nitroluks"
CRYPT_PATCH="https://raw.githubusercontent.com/amedeos/amedeos.github.io/master/scripts/00-crypt.sh.patch"
GENKERNEL_DIR="/usr/share/genkernel/defaults/initrd.d"
CRYPT_FILE="00-crypt.sh"
GIT_BIN=`which git`
GPLUS_BIN=`which g++`
CURL_BIN=`which curl`
#TODO: insert return codes and check them after every commands

# copy libnitrokey
cp /usr/lib64/libnitrokey.so* ${INITRAMFS_OVERLAY}/usr/lib64/
# copy libhidapi-libusb and libusb
cp /usr/lib64/libhidapi-libusb.so.0* ${INITRAMFS_OVERLAY}/usr/lib64/
cp /lib64/libusb-1.0.so.0* ${INITRAMFS_OVERLAY}/lib64/

NITROBUILD=$(mktemp -t -d nitrobuild.XXXXX)
${GIT_BIN} clone ${NITROLUKS} ${NITROBUILD}
mkdir -p ${NITROBUILD}/build
${GPLUS_BIN} ${NITROBUILD}/src/nitro_luks.c -o ${NITROBUILD}/build/nitro_luks -L${NITROBUILD}/build/ -l:libnitrokey.so.3 -Wall
cp ${NITROBUILD}/build/nitro_luks ${INITRAMFS_OVERLAY}/bin/
${CURL_BIN} --output ${NITROBUILD}/00-crypt.sh.patch ${CRYPT_PATCH}
cp ${GENKERNEL_DIR}/${CRYPT_FILE} ${NITROBUILD}/${CRYPT_FILE}
patch ${NITROBUILD}/${CRYPT_FILE} ${NITROBUILD}/00-crypt.sh.patch
cp ${NITROBUILD}/${CRYPT_FILE} ${INITRAMFS_OVERLAY}/etc/initrd.d/${CRYPT_FILE}
rm -rf ${NITROBUILD}
# we need to raise this file in the future, otherwise genkernel will overwrite it in initramfs
TZ=ZZZ0 touch -t "$(TZ=ZZZ-1:30 date +%Y%m%d%H%M.%S)" ${INITRAMFS_OVERLAY}/etc/initrd.d/${CRYPT_FILE}

Build a new kernel and a new initramfs

Let’s create a new kernel and a new initramfs with genkernel

# time genkernel --luks --lvm all

Configure grub

It’s time to configure grub

# grub-mkconfig -o /boot/grub/grub.cfg

Reboot

Now, you can reboot your box and unlock LUKS with your Nitrokey.