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diff --git a/README.md b/README.md new file mode 100644 index 0000000..b452530 --- /dev/null +++ b/README.md @@ -0,0 +1,72 @@ +# cryptsetup-nuke-password + +Installing this package lets you configure a special "nuke password" that +can be used to destroy the encryption keys required to unlock the encrypted +partitions. This password can be entered in the usual early-boot prompt +asking the passphrase to unlock the encrypted partition(s). + +This provides a relatively stealth way to make your data unreadable in +case you fear that your computer is going to be seized. + +## How can I configure the nuke password + +After having installed the package, just run “dpkg-reconfigure +cryptsetup-nuke-password”. Behind the scene, this creates +`/etc/cryptsetup-nuke-password/password_hash` with +the output of `echo your-password | +/usr/lib/cryptsetup-nuke-password/crypt --generate` and rebuilds +the initramfs (`update-initramfs -u`). + +## How does it work? + +The packages diverts /lib/cryptsetup/askpass by our own script that will +call the original tool to get the password but that will do its own +treatment before outputting the same password to stdout... + +To identify the partition being unlocked, we rely on the environment +variables exported by +/usr/share/initramfs-tools/scripts/local-top/cryptroot + +To destroy the encryption keys, we call `cryptsetup erase <device>`. + +## How to configure the nuke password non-interactively + +You need to preseed the password in the debconf database and then +run dpkg-reconfigure in a way where it is not allowed to ask question: +``` +$ sudo debconf-set-selections <<END +cryptsetup-nuke-password cryptsetup-nuke-password/password string Th3Pa$$w0rd +cryptsetup-nuke-password cryptsetup-nuke-password/password-again string Th3Pa$$w0rd +END +$ sudo dpkg-reconfigure -f noninteractive cryptsetup-nuke-password +``` + +## Backing up the encryption key + +If you expect to make use of this nuke password, then you should consider +backing up the luks header. That way, if your computer is seized, and then +later given back to you, you will be able to restore the luks headers and +get back access to your data. + +Here's the command to use (replace `<device>` with the path of the device +file representing your luks encrypted partition, and `<your-backup-file>` +with the path to the backup file to create): +``` +$ sudo cryptsetup luksHeaderBackup <device> --header-backup-file <your-backup-file> +``` + +To later restore the header, you will have to do: +``` +$ sudo cryptsetup luksHeaderRestore <device> --header-backup-file <your-backup-file> +``` + +## Limitations + +Due to the way this feature is implemented, it can't be used if you +configure cryptsetup to use something else than an interactive password +to unlock the encryption keys. + +It is also not usable on a live image (unless you configured the nuke +password with debconf preseeding at the time you generated the live image) +since it needs to regenerate the initrd to embed itself and the nuke +password. |