clevis(1) - Automated decryption policy framework.

[hoodedvul]

CLEVIS(1)                                                            CLEVIS(1)

NAME
       clevis - Automated decryption policy framework

SYNOPSIS
       clevis COMMAND [OPTIONS]

OVERVIEW
       Clevis is a framework for automated decryption policy. It allows you to
       define a policy at encryption time that must be satisfied for the data
       to decrypt. Once this policy is met, the data is decrypted.

       Clevis is pluggable. Our plugins are called pins. The job of a pin is
       to take a policy as its first argument and plaintext on standard input
       and to encrypt the data so that it can be automatically decrypted if
       the policy is met. Lets walk through an example.

TANG BINDING
       Clevis provides support for the Tang network binding server. Tang
       provides a stateless, lightweight alternative to escrows. Encrypting
       data using the Tang pin works much like our HTTP pin above:

           $ clevis encrypt tang '{"url":"http://tang.srv"}' < PT > JWE
           The advertisement contains the following signing keys:

           _OsIk0T-E2l6qjfdDiwVmidoZjA

           Do you wish to trust these keys? [ynYN] y

       As you can see above, Tang utilizes a trust-on-first-use workflow.
       Alternatively, Tang can perform entirely offline encryption if you
       pre-share the server advertisement. Decryption, too works like our
       first example:

           $ clevis decrypt < JWE > PT

       For more information, see clevis-encrypt-tang(1).

TPM2 BINDING
       Clevis provides support to encrypt a key in a Trusted Platform Module
       2.0 (TPM2) chip. The cryptographically-strong, random key used for
       encryption is encrypted using the TPM2 chip, and then at decryption
       time is decrypted using the TPM2 to allow clevis to decrypt the secret
       stored in the JWE.

       Encrypting data using the tpm2 pin works the same than the pins
       mentioned above:

           $ clevis encrypt tpm2 '{}' < PT > JWE

       The pin has reasonable defaults for its configuration, but a different
       hierarchy, hash, and key algorithms can be chosen if the defaults used
       are not suitable.

       Decryption also works similar to other pins, only the JWE needs to be
       provided:

           $ clevis decrypt < JWE > PT

       Note that like other pins no configuration is used for decryption, this
       is due clevis storing the public and private keys to unseal the TPM2
       encrypted object in the JWE so clevis can fetch that information from
       there.

       For more information see clevis-encrypt-tpm2(1).

SHAMIR’S SECRET SHARING
       Clevis provides a way to mix pins together to create sophisticated
       unlocking and high availability policies. This is accomplished by using
       an algorithm called Shamir’s Secret Sharing (SSS).

       SSS is a thresholding scheme. It creates a key and divides it into a
       number of pieces. Each piece is encrypted using another pin (possibly
       even SSS recursively). Additionally, you define the threshold t. If at
       least t pieces can be decrypted, then the encryption key can be
       recovered and decryption can succeed.

       For example, let’s create a high-availability setup using Tang:

           $ cfg='{"t":1,"pins":{"tang":[{"url":...},{"url":...}]}}'
           $ clevis encrypt sss "$cfg" < PT > JWE

       In this policy, we are declaring that we have a threshold of 1, but
       that there are multiple key fragments encrypted using different Tang
       servers. Since our threshold is 1, so long as any of the Tang servers
       are available, decryption will succeed. As always, decryption is
       simply:

           $ clevis decrypt < JWE > PT

       For more information, see clevis-encrypt-tang(1).

LUKS BINDING
       Clevis can be used to bind an existing LUKS volume to its automation
       policy. This is accomplished with a simple command:

           $ clevis luks bind -d /dev/sda tang '{"url":...}'

       This command performs four steps:

        1. Creates a new key with the same entropy as the LUKS master key.

        2. Encrypts the new key with Clevis.

        3. Stores the Clevis JWE in the LUKS header with LUKSMeta.

        4. Enables the new key for use with LUKS.

       This disk can now be unlocked with your existing password as well as
       with the Clevis policy. Clevis provides two unlockers for LUKS volumes.
       First, we provide integration with Dracut to automatically unlock your
       root volume during early boot. Second, we provide integration with
       UDisks2 to automatically unlock your removable media in your desktop
       session.

       For more information, see clevis-luks-bind(1).

SEE ALSO
       clevis-encrypt-tang(1), clevis-encrypt-tpm2(1), clevis-encrypt-sss(1),
       clevis-luks-bind(1), clevis-decrypt(1)

                                  02/02/2020                         CLEVIS(1)