nixpkgs/nixos/modules/system/boot/clevis.md

Clevis

Clevis is a framework for automated decryption of resources. Clevis allows for secure unattended disk decryption during boot, using decryption policies that must be satisfied for the data to decrypt.

Create a JWE file containing your secret

The first step is to embed your secret in a JWE file. JWE files have to be created through the clevis command line. 3 types of policies are supported:

1. TPM policies

Secrets are pinned against the presence of a TPM2 device, for example:

echo -n hi | clevis encrypt tpm2 '{}' > hi.jwe

2. Tang policies

Secrets are pinned against the presence of a Tang server, for example:

echo -n hi | clevis encrypt tang '{"url": "http://tang.local"}' > hi.jwe

3. Shamir Secret Sharing

Using Shamir's Secret Sharing (sss), secrets are pinned using a combination of the two preceding policies. For example:

echo -n hi | clevis encrypt sss \
'{"t": 2, "pins": {"tpm2": {"pcr_ids": "0"}, "tang": {"url": "http://tang.local"}}}' \
> hi.jwe

For more complete documentation on how to generate a secret with clevis, see the clevis documentation.

Activate unattended decryption of a resource at boot

In order to activate unattended decryption of a resource at boot, enable the clevis module:

{
  boot.initrd.clevis.enable = true;
}

Then, specify the device you want to decrypt using a given clevis secret. Clevis will automatically try to decrypt the device at boot and will fallback to interactive unlocking if the decryption policy is not fulfilled.

{
  boot.initrd.clevis.devices."/dev/nvme0n1p1".secretFile = ./nvme0n1p1.jwe;
}

Only bcachefs, zfs and luks encrypted devices are supported at this time.