initrd_luks_pkcs

Acknowledgment

It has been tested on a debian laptop and a mobian pinephone. The smartcard generation come from inspired by https://github.com/swoopla/smartcard-luks . The OSK-SDL parts are inspired by Mobian package https://salsa.debian.org/DebianOnMobile-team/osk-sdl.

Single key setup

General steps:

• Erase and initialize card
• Create public/private key pair on smartcard
• Create key file and add it to a LUKS key slot
• Encrypt key file using public key from smartcard
• Modify initramfs to use smartcard to decrypt the encrypted keyfile
• Modify decrypt_opensc script to swicth between smartcard and luks password and add osk-sdl support for touchscreen device

details:

1. Install smartcard middleware

   sudo apt-get install pcscd opensc

2. Erase smartcard

   pkcs15-init -E

3. Initialize smartcard

   pkcs15-init --create-pkcs15 -p pkcs15+onepin --pin 1234 --puk 4321

4. Create public/private key pair on smartcard

   pkcs15-init -G rsa/2048 -i 01 -a 01 -u decrypt --pin 1234

5. Create a random key file and add it to a LUKS key slot

   sudo touch /root/rootkey

   sudo chmod 600 /root/rootkey

   sudo dd if=/dev/random of=/root/rootkey bs=1 count=245 #change to urandom if you can't wait

   sudo cryptsetup luksAddKey /dev/sda2 /root/rootkey

6. Export the public key from smartcard

   pkcs15-tool --read-public-key 01 -o public_key_rsa2048.pem

7. Encrypt key file using public key

   sudo openssl rsautl -encrypt -pubin -inkey public_key_rsa2048.pem -in /root/rootkey -out /root/rootkey.enc

   sudo rm /root/rootkey

8. Edit crypttab. This change sends the encrypted key file as a param to the keyscript

   This should be of the form:

   mapped_device_name source_block_device key_file luks,keyscript=decrypt_pkcs

   For example:

   sda2_crypt UUID=d332ecc5-ce8b-4900-a04a-a79abd029d6d /root/rootkey.enc luks,keyscript=decrypt_pkcs

9. Install the cryptsetup script and the initramfs-tool hook

   sudo cp lib/cryptsetup/scripts/decrypt_pkcs /lib/cryptsetup/scripts/

   sudo cp etc/initramfs-tools/hooks/decrypt_pkcs /etc/initramfs-tools/hooks && sudo chmod +x /etc/initramfs-tools/hooks/decrypt_pkcs

   sudo cp etc/default/decrypt_pkcs /etc/default/

   sudo update-initramfs -u

10. Test smartcard (without USB Key)

11. Test LUKS Password (without Smartcard)

Multi keys setup

The setup is quite the same except that you need to put all the key files in the expected format. With the provided exemple config and script all keys must be stored in the /etc/keys folder with the following filename : internal-${ENCODED_SERIAL}.enc with `${ENCODED_SERIAL} the result of the following commands :

pkcs15-tool -c 2>/dev/null  | awk '{ if ($1$2=="Encodedserial") {print $NF}}'

You need to modify the /etc/default/decrypt_pkcs and set DECIPHER_MULTI to 1

and copy the script in charge of selecting the right key file form initramfs :

```sudo mkdir -p /usr/share/decrypt_pkcs && sudo cp usr/share/decrypt_pkcs/pkcs15_get-key.sh /usr/share/decrypt_pkcs/ && sudo chmod +x /usr/share/decrypt_pkcs/pkcs15_get-key.sh ```

Every time a new key is added, the initrd mus be regenerated :

```sudo update-initramfs -u```