systemd-creds — Lists, shows, encrypts and decrypts service credentials
systemd-creds [OPTIONS...] COMMAND [ARGS...]
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 documentation.
The following commands are understood:
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).
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.
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.
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:
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.
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.
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.
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.
-h, --help¶--version¶--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.
--user¶When specified with the encrypt and decrypt
commands encrypts a user-scoped (rather than a system-scoped) credential. Use --uid=
to select which user the credential is from. Such credentials may only be decrypted from the
specified user's context, except if privileges can be acquired. Generally, when an encrypted
credential shall be used in the per-user service manager it should be encrypted with this option set,
when it shall be used in the system service manager it should be encrypted without.
Internally, this ensures that the selected user's numeric UID and username, as well as the system's machine-id(5) are incorporated into the encryption key.
--uid=¶Specifies the user to encrypt the credential for. Takes a user name or numeric
UID. If set, implies --user. If set to the special string "self"
sets the user to the user of the calling process. If --user is used without
--uid= then --uid=self is implied, i.e. the credential is encrypted
for the calling user.
--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.
--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.
--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.
--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.
--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.
--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).
--with-key=, -H, -T¶When specified with the encrypt command controls the
encryption/signature key to use. Takes one of "host", "tpm2",
"host+tpm2", "null", "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
"null" 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 "null" 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.
--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.
--tpm2-pcrs=PCR[+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).
--tpm2-public-key=PATH, --tpm2-public-key-pcrs=PCR[+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.
--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.
--allow-null¶Allow decrypting credentials that use an empty key.
--quiet, -q¶Suppress additional output.
--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).
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