Index · Directives systemd 249

Name

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

Synopsis

systemd-creds [OPTIONS...]

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 LoadCredential=, SetCredential=, LoadCredentialEncrypted= and SetCredentialEncrypted= settings, see systemd.exec(5) for details.

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).

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.

setup

Generates a host encryption key for credentials, if none has been generated before. 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.

encrypt input output

Loads the specified (unencrypted plaintext) input credential file, encrypts it and writes the (encrypted ciphertext) version to the specified output 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 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 initial RAM disk (initrd) of the system 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.

decrypt input [output]

Undoes the effect of the encrypt operation: loads the specified (encrypted ciphertext) input credential file, decrypts it and writes the (decrypted plaintext) version to the specified output 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 only one path is specified (or the output path specified as "-") it is taken as input path and the decrypted credential is written to standard output. If the input path is specified as "-" the encrypted credential is read from standard input. 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

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.

--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.

--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(5).

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(5).

--with-key=, -H, -T

When specified with the encrypt command controls the encryption key to use. Takes one of "host", "tpm2", "host+tpm2" or "auto". 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.

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 initial RAM disk (initrd) where /var/lib/systemd/ is typically not available make sure to use --with-key=tpm2 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...]

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).

--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.

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 | systemd-creds encrypt --name=mysql-password -p - - > /etc/systemd/system/xyz.service.d/50-password.conf
# systemctl daemon-reload
# systemctl restart xyz.service

See Also

systemd(1), systemd.exec(5)