clevis-encrypt-tpm2(1) - Encrypts using a TPM2.0 chip binding policy.

[hoodedvul]

CLEVIS-ENCRYPT-TPM(1)                                    CLEVIS-ENCRYPT-TPM(1)

NAME
       clevis-encrypt-tpm2 - Encrypts using a TPM2.0 chip binding policy

SYNOPSIS
       clevis encrypt tpm2 CONFIG < PT > JWE

OVERVIEW
       The clevis encrypt tpm2 command encrypts using a Trusted Platform
       Module 2.0 (TPM2) chip. Its only argument is the JSON configuration
       object.

       When using the tpm2 pin, we create a new, cryptographically-strong,
       random key. This key is encrypted using the TPM2 chip. Then at
       decryption time, the key is decrypted again using the TPM2 chip.

           $ 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:

           $ clevis encrypt tpm2 '{"hash":"sha1","key":"rsa"}' < PT > JWE

       To decrypt the data, simply provide the ciphertext (JWE):

           $ 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.

       The pin also supports sealing data to a Platform Configuration
       Registers (PCR) state. That way the data can only be unsealed if the
       PCRs hashes values match the policy used when sealing.

       For example, to seal the data to the PCR with index 0 and 1 for the
       SHA1 bank:

           $ clevis encrypt tpm2 '{"pcr_bank":"sha1","pcr_ids":"0,1"}' < PT > JWE

       The PCR digest values are looked up from the current hash values for
       the PCRs, but a digest can also be provided if the data needs to be
       sealed with values different to the current ones, by passing the binary
       hash encoded in base64:

           $ clevis encrypt tpm2 '{"pcr_ids":"0","pcr_digest":"xy7J5svCtqlfM03d1lE5gdoA8MI"}' < PT > JWE

THREAT MODEL
       The Clevis security model relies in the fact that an attacker will not
       be able to access both the encrypted data and the decryption key.

       For most Clevis pins, the decryption key is not locally stored, so the
       decryption policy is only satisfied if the decryption key can be
       remotely accessed. It could for example be stored in a remote server or
       in a hardware authentication device that has to be plugged into the
       machine.

       The tpm2 pin is different in this regard, since a key is wrapped by a
       TPM2 chip that is always present in the machine. This does not mean
       that there are not use cases for this pin, but it is important to
       understand the fact that an attacker that has access to both the
       encrypted data and the local TPM2 chip will be able to decrypt the
       data.

CONFIG
       This command uses the following configuration properties:

       ·   hash (string) : Hash algorithm used in the computation of the
           object name (default: sha256)

               It must be one of the following:

           ·   sha1

           ·   sha256

           ·   sha384

           ·   sha512

           ·   sm3_256

       ·   key (string) : Algorithm type for the generated key (default: ecc)

               It must be one of the following:

           ·   rsa

           ·   keyedhash

           ·   ecc

           ·   symcipher

       ·   pcr_bank (string) : PCR algorithm bank to use for policy (default:
           sha1)

               It must be one of the following:

           ·   sha1

           ·   sha256

       ·   pcr_ids (string) : Comma separated list of PCR used for policy. If
           not present, no policy is used

       ·   pcr_digest (string) : Binary PCR hashes encoded in base64. If not
           present, the hash values are looked up

SEE ALSO
       clevis-decrypt(1)

                                  02/02/2020             CLEVIS-ENCRYPT-TPM(1)