Ubuntu Manpage: systemd-creds - Lists, shows, encrypts and decrypts service credentials

Provided by: systemd_255.4-1ubuntu8.4_amd64

NAME

       systemd-creds - Lists, shows, encrypts and decrypts service credentials

SYNOPSIS

       systemd-creds [OPTIONS...] COMMAND [ARGS...]

DESCRIPTION

       systemd-creds is a tool for listing, showing, encrypting and decrypting unit credentials.
       Credentials are limited-size binary or textual objects that may be passed to unit
       processes. They are primarily used for passing cryptographic keys (both public and
       private) or certificates, user account information or identity information from the host
       to services.

       Credentials are configured in unit files via the ImportCredential=, LoadCredential=,
       SetCredential=, LoadCredentialEncrypted=, and SetCredentialEncrypted= settings, see
       systemd.exec(5) for details.

       For further information see System and Service Credentials[1] documentation.

COMMANDS

The following commands are understood:

list
Show a list of credentials passed into the current execution context. This command
shows the files in the directory referenced by the $CREDENTIALS_DIRECTORY environment
variable, and is intended to be executed from within service context.

Along with each credential name, the size and security state is shown. The latter is
one of "secure" (in case the credential is backed by unswappable memory, i.e.
"ramfs"), "weak" (in case it is backed by any other type of memory), or "insecure" (if
having any access mode that is not 0400, i.e. if readable by anyone but the owner).

Added in version 250.

cat credential...
Show contents of specified credentials passed into the current execution context.
Takes one or more credential names, whose contents shall be written to standard
output.

When combined with --json= or --transcode= the output is transcoded in simple ways
before outputting.

Added in version 250.

setup
Generates a host encryption key for credentials, if one has not been generated
already. This ensures the /var/lib/systemd/credential.secret file is initialized with
a random secret key if it doesn't exist yet. This secret key is used when
encrypting/decrypting credentials with encrypt or decrypt, and is only accessible to
the root user. Note that there's typically no need to invoke this command explicitly
as it is implicitly called when encrypt is invoked, and credential host key encryption
selected.

Added in version 250.

encrypt input|- output|-
Loads the specified (unencrypted plaintext) input credential file, encrypts it and
writes the (encrypted ciphertext) output to the specified target credential file. The
resulting file may be referenced in the LoadCredentialEncrypted= setting in unit
files, or its contents used literally in SetCredentialEncrypted= settings.

Takes two file system paths. The file name part of the output path is embedded as name
in the encrypted credential, to ensure encrypted credentials cannot be renamed and
reused for different purposes without this being noticed. The credential name to embed
may be overridden with the --name= setting. The input or output paths may be specified
as "-", in which case the credential data is read from/written to standard input and
standard output. If the output path is specified as "-" the credential name cannot be
derived from the file system path, and thus should be specified explicitly via the
--name= switch.

The credential data is encrypted and authenticated symmetrically with one of the
following encryption keys:

1. A secret key automatically derived from the system's TPM2 chip. This encryption
key is not stored on the host system and thus decryption is only possible with
access to the original TPM2 chip. Or in other words, the credential secured in
this way can only be decrypted again by the local machine.

2. A secret key stored in the /var/lib/systemd/credential.secret file which is only
accessible to the root user. This "host" encryption key is stored on the host file
system, and thus decryption is possible with access to the host file system and
sufficient privileges. The key is automatically generated when needed, but can
also be created explicitly with the setup command, see above.

3. A combination of the above: an encryption key derived from both the TPM2 chip and
the host file system. This means decryption requires both access to the original
TPM2 chip and the OS installation. This is the default mode of operation if a TPM2
chip is available and /var/lib/systemd/ resides on persistent media.

Which of the three keys shall be used for encryption may be configured with the
--with-key= switch. Depending on the use-case for the encrypted credential the key to
use may differ. For example, for credentials that shall be accessible from the initrd,
encryption with the host key is not appropriate, since access to the host key is
typically not available from the initrd. Thus, for such credentials only the TPM2 key
should be used.

Encrypted credentials are always encoded in Base64.

Use decrypt (see below) to undo the encryption operation, and acquire the decrypted
plaintext credential from the encrypted ciphertext credential.

The credential data is encrypted using AES256-GCM, i.e. providing both confidentiality
and integrity, keyed by a SHA256 hash of one or both of the secret keys described
above.

Added in version 250.

decrypt input|- [output|-]
Undoes the effect of the encrypt operation: loads the specified (encrypted ciphertext)
input credential file, decrypts and authenticates it and writes the (decrypted
plaintext) output to the specified target credential file.

Takes one or two file system paths. The file name part of the input path is compared
with the credential name embedded in the encrypted file. If it does not match
decryption fails. This is done in order to ensure that encrypted credentials are not
re-purposed without this being detected. The credential name to compare with the
embedded credential name may also be overridden with the --name= switch. If the input
path is specified as "-", the encrypted credential is read from standard input. If
only one path is specified or the output path specified as "-", the decrypted
credential is written to standard output. In this mode, the expected name embedded in
the credential cannot be derived from the path and should be specified explicitly with
--name=.

Decrypting credentials requires access to the original TPM2 chip and/or credentials
host key, see above. Information about which keys are required is embedded in the
encrypted credential data, and thus decryption is entirely automatic.

Added in version 250.

has-tpm2
Reports whether the system is equipped with a TPM2 device usable for protecting
credentials. If a TPM2 device has been discovered, is supported, and is being used by
firmware, by the OS kernel drivers and by userspace (i.e. systemd) this prints "yes"
and exits with exit status zero. If no such device is discovered/supported/used,
prints "no". Otherwise prints "partial". In either of these two cases exits with
non-zero exit status. It also shows four lines indicating separately whether firmware,
drivers, the system and the kernel discovered/support/use TPM2.

Combine with --quiet to suppress the output.

Added in version 251.

-h, --help
Print a short help text and exit.

--version
Print a short version string and exit.

OPTIONS

--system
When specified with the list and cat commands operates on the credentials passed to
system as a whole instead of on those passed to the current execution context. This is
useful in container environments where credentials may be passed in from the container
manager.

Added in version 250.

--transcode=
When specified with the cat or decrypt commands, transcodes the output before showing
it. Takes one of "base64", "unbase64", "hex" or "unhex" as argument, in order to
encode/decode the credential data with Base64 or as series of hexadecimal values.

Note that this has no effect on the encrypt command, as encrypted credentials are
unconditionally encoded in Base64.

Added in version 250.

--newline=
When specified with cat or decrypt controls whether to add a trailing newline
character to the end of the output if it doesn't end in one, anyway. Takes one of
"auto", "yes" or "no". The default mode of "auto" will suffix the output with a single
newline character only when writing credential data to a TTY.

Added in version 250.

--pretty, -p
When specified with encrypt controls whether to show the encrypted credential as
SetCredentialEncrypted= setting that may be pasted directly into a unit file. Has
effect only when used together with --name= and "-" as the output file.

Added in version 250.

--name=name
When specified with the encrypt command controls the credential name to embed in the
encrypted credential data. If not specified the name is chosen automatically from the
filename component of the specified output path. If specified as empty string no
credential name is embedded in the encrypted credential, and no verification of
credential name is done when the credential is decrypted.

When specified with the decrypt command control the credential name to validate the
credential name embedded in the encrypted credential with. If not specified the name
is chosen automatically from the filename component of the specified input path. If no
credential name is embedded in the encrypted credential file (i.e. the --name= with an
empty string was used when encrypted) the specified name has no effect as no
credential name validation is done.

Embedding the credential name in the encrypted credential is done in order to protect
against reuse of credentials for purposes they weren't originally intended for, under
the assumption the credential name is chosen carefully to encode its intended purpose.

Added in version 250.

--timestamp=timestamp
When specified with the encrypt command controls the timestamp to embed into the
encrypted credential. Defaults to the current time. Takes a timestamp specification in
the format described in systemd.time(7).

When specified with the decrypt command controls the timestamp to use to validate the
"not-after" timestamp that was configured with --not-after= during encryption. If not
specified defaults to the current system time.

Added in version 250.

--not-after=timestamp
When specified with the encrypt command controls the time when the credential shall
not be used anymore. This embeds the specified timestamp in the encrypted credential.
During decryption the timestamp is checked against the current system clock, and if
the timestamp is in the past the decryption will fail. By default no such timestamp is
set. Takes a timestamp specification in the format described in systemd.time(7).

Added in version 250.

--with-key=, -H, -T
When specified with the encrypt command controls the encryption/signature key to use.
Takes one of "host", "tpm2", "host+tpm2", "tpm2-absent", "auto", "auto-initrd". See
above for details on the three key types. If set to "auto" (which is the default) the
TPM2 key is used if a TPM2 device is found and not running in a container. The host
key is used if /var/lib/systemd/ is on persistent media. This means on typical systems
the encryption is by default bound to both the TPM2 chip and the OS installation, and
both need to be available to decrypt the credential again. If "auto" is selected but
neither TPM2 is available (or running in container) nor /var/lib/systemd/ is on
persistent media, encryption will fail. If set to "tpm2-absent" a fixed zero length
key is used (thus, in this mode no confidentiality nor authenticity are provided!).
This logic is useful to cover for systems that lack a TPM2 chip but where credentials
shall be generated. Note that decryption of such credentials is refused on systems
that have a TPM2 chip and where UEFI SecureBoot is enabled (this is done so that such
a locked down system cannot be tricked into loading a credential generated this way
that lacks authentication information). If set to "auto-initrd" a TPM2 key is used if
a TPM2 is found. If not a fixed zero length key is used, equivalent to "tpm2-absent"
mode. This option is particularly useful to generate credentials files that are
encrypted/authenticated against TPM2 where available but still work on systems lacking
support for this.

The -H switch is a shortcut for --with-key=host. Similar, -T is a shortcut for
--with-key=tpm2.

When encrypting credentials that shall be used in the initrd (where /var/lib/systemd/
is typically not available) make sure to use --with-key=auto-initrd mode, to disable
binding against the host secret.

This switch has no effect on the decrypt command, as information on which key to use
for decryption is included in the encrypted credential already.

Added in version 250.

--tpm2-device=PATH
Controls the TPM2 device to use. Expects a device node path referring to the TPM2 chip
(e.g. /dev/tpmrm0). Alternatively the special value "auto" may be specified, in order
to automatically determine the device node of a suitable TPM2 device (of which there
must be exactly one). The special value "list" may be used to enumerate all suitable
TPM2 devices currently discovered.

Added in version 250.

--tpm2-pcrs= [PCR...]
Configures the TPM2 PCRs (Platform Configuration Registers) to bind the encryption key
to. Takes a "+" separated list of numeric PCR indexes in the range 0...23. If not
used, defaults to PCR 7 only. If an empty string is specified, binds the encryption
key to no PCRs at all. For details about the PCRs available, see the documentation of
the switch of the same name for systemd-cryptenroll(1).

Added in version 250.

--tpm2-public-key= [PATH], --tpm2-public-key-pcrs= [PCR...]
Configures a TPM2 signed PCR policy to bind encryption to, for use with the encrypt
command. The --tpm2-public-key= option accepts a path to a PEM encoded RSA public key,
to bind the encryption to. If this is not specified explicitly, but a file
tpm2-pcr-public-key.pem exists in one of the directories /etc/systemd/, /run/systemd/,
/usr/lib/systemd/ (searched in this order), it is automatically used. The
--tpm2-public-key-pcrs= option takes a list of TPM2 PCR indexes to bind to (same
syntax as --tpm2-pcrs= described above). If not specified defaults to 11 (i.e. this
binds the policy to any unified kernel image for which a PCR signature can be
provided).

Note the difference between --tpm2-pcrs= and --tpm2-public-key-pcrs=: the former binds
decryption to the current, specific PCR values; the latter binds decryption to any set
of PCR values for which a signature by the specified public key can be provided. The
latter is hence more useful in scenarios where software updates shall be possible
without losing access to all previously encrypted secrets.

Added in version 252.

--tpm2-signature= [PATH]
Takes a path to a TPM2 PCR signature file as generated by the systemd-measure(1) tool
and that may be used to allow the decrypt command to decrypt credentials that are
bound to specific signed PCR values. If this is not specified explicitly, and a
credential with a signed PCR policy is attempted to be decrypted, a suitable signature
file tpm2-pcr-signature.json is searched for in /etc/systemd/, /run/systemd/,
/usr/lib/systemd/ (in this order) and used.

Added in version 252.

--quiet, -q
When used with has-tpm2 suppresses the output, and only returns an exit status
indicating support for TPM2.

Added in version 251.

--no-pager
Do not pipe output into a pager.

--no-legend
Do not print the legend, i.e. column headers and the footer with hints.

--json=MODE
Shows output formatted as JSON. Expects one of "short" (for the shortest possible
output without any redundant whitespace or line breaks), "pretty" (for a pretty
version of the same, with indentation and line breaks) or "off" (to turn off JSON
output, the default).

EXIT STATUS

       On success, 0 is returned.

       In case of the has-tpm2 command returns 0 if a TPM2 device is discovered, supported and
       used by firmware, driver, and userspace (i.e. systemd). Otherwise returns the OR
       combination of the value 1 (in case firmware support is missing), 2 (in case driver
       support is missing) and 4 (in case userspace support is missing). If no TPM2 support is
       available at all, value 7 is hence returned.

EXAMPLES

       Example 1. Encrypt a password for use as credential

       The following command line encrypts the specified password "hunter2", writing the result
       to a file password.cred.

           # echo -n hunter2 | systemd-creds encrypt - password.cred

       This decrypts the file password.cred again, revealing the literal password:

           # systemd-creds decrypt password.cred
           hunter2

       Example 2. Encrypt a password and include it in a unit file

       The following command line prompts the user for a password and generates a
       SetCredentialEncrypted= line from it for a credential named "mysql-password", suitable for
       inclusion in a unit file.

           # systemd-ask-password -n | systemd-creds encrypt --name=mysql-password -p - -
           🔐 Password: ****
           SetCredentialEncrypted=mysql-password: \
                   k6iUCUh0RJCQyvL8k8q1UyAAAAABAAAADAAAABAAAAASfFsBoPLIm/dlDoGAAAAAAAAAA \
                   NAAAAAgAAAAAH4AILIOZ3w6rTzYsBy9G7liaCAd4i+Kpvs8mAgArzwuKxd0ABDjgSeO5k \
                   mKQc58zM94ZffyRmuNeX1lVHE+9e2YD87KfRFNoDLS7F3YmCb347gCiSk2an9egZ7Y0Xs \
                   700Kr6heqQswQEemNEc62k9RJnEl2q7SbcEYguegnPQUATgAIAAsAAAASACA/B90W7E+6 \
                   yAR9NgiIJvxr9bpElztwzB5lUJAxtMBHIgAQACCaSV9DradOZz4EvO/LSaRyRSq2Hj0ym \
                   gVJk/dVzE8Uxj8H3RbsT7rIBH02CIgm/Gv1ukSXO3DMHmVQkDG0wEciyageTfrVEer8z5 \
                   9cUQfM5ynSaV2UjeUWEHuz4fwDsXGLB9eELXLztzUU9nsAyLvs3ZRR+eEK/A==

       The generated line can be pasted 1:1 into a unit file, and will ensure the acquired
       password will be made available in the $CREDENTIALS_DIRECTORY/mysql-password credential
       file for the started service.

       Utilizing the unit file drop-in logic this can be used to securely pass a password
       credential to a unit. A similar, more comprehensive set of commands to insert a password
       into a service xyz.service:

           # mkdir -p /etc/systemd/system/xyz.service.d
           # systemd-ask-password -n | ( echo "[Service]" && systemd-creds encrypt --name=mysql-password -p - - ) >/etc/systemd/system/xyz.service.d/50-password.conf
           # systemctl daemon-reload
           # systemctl restart xyz.service

NOTES

        1. System and Service Credentials
           https://systemd.io/CREDENTIALS

NAME

SYNOPSIS

DESCRIPTION

COMMANDS

OPTIONS

EXIT STATUS

EXAMPLES

SEE ALSO

NOTES