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0bada3f8b7
Let's document this for now. We should be able to lift these limitations sooner or later, at which point we can drop this documentation again. These two limitations are a pitfall that people should be aware of, before going FIDO2-only. See: #20230 #19208
361 lines
19 KiB
XML
361 lines
19 KiB
XML
<?xml version="1.0"?>
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<!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd-cryptenroll" xmlns:xi="http://www.w3.org/2001/XInclude" conditional='HAVE_LIBCRYPTSETUP'>
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<refentryinfo>
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<title>systemd-cryptenroll</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-cryptenroll</refentrytitle>
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<manvolnum>1</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-cryptenroll</refname>
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<refpurpose>Enroll PKCS#11, FIDO2, TPM2 token/devices to LUKS2 encrypted volumes</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>systemd-cryptenroll <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="opt">DEVICE</arg></command>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><command>systemd-cryptenroll</command> is a tool for enrolling hardware security tokens and devices
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into a LUKS2 encrypted volume, which may then be used to unlock the volume during boot. Specifically, it
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supports tokens and credentials of the following kind to be enrolled:</para>
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<orderedlist>
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<listitem><para>PKCS#11 security tokens and smartcards that may carry an RSA key pair (e.g. various
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YubiKeys)</para></listitem>
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<listitem><para>FIDO2 security tokens that implement the <literal>hmac-secret</literal> extension (most
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FIDO2 keys, including YubiKeys)</para></listitem>
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<listitem><para>TPM2 security devices</para></listitem>
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<listitem><para>Recovery keys. These are similar to regular passphrases, however are randomly generated
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on the computer and thus generally have higher entropy than user-chosen passphrases. Their character
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set has been designed to ensure they are easy to type in, while having high entropy. They may also be
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scanned off screen using QR codes. Recovery keys may be used for unlocking LUKS2 volumes wherever
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passphrases are accepted. They are intended to be used in combination with an enrolled hardware
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security token, as a recovery option when the token is lost.</para></listitem>
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<listitem><para>Regular passphrases</para></listitem>
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</orderedlist>
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<para>In addition, the tool may be used to enumerate currently enrolled security tokens and wipe a subset
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of them. The latter may be combined with the enrollment operation of a new security token, in order to
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update or replace enrollments.</para>
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<para>The tool supports only LUKS2 volumes, as it stores token meta-information in the LUKS2 JSON token
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area, which is not available in other encryption formats.</para>
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</refsect1>
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<refsect1>
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<title>Limitations</title>
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<para>Note that currently when enrolling a new key of one of the five supported types listed above, it is
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required to first provide a passphrase or recovery key (i.e. one of the latter two key types). For
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example, it's currently not possible to unlock a device with a FIDO2 key in order to enroll a new FIDO2
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key. Instead, in order to enroll a new FIDO2 key, it is necessary to provide an already enrolled regular
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passphrase or recovery key. Thus, if in future key roll-over is desired it's generally recommended to
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combine TPM2, FIDO2, PKCS#11 key enrollment with enrolling a regular passphrase or recovery key.</para>
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<para>Also note that support for enrolling multiple FIDO2 tokens is currently not too useful, as while
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unlocking <command>systemd-cryptsetup</command> cannot identify which token is currently plugged in and
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thus does not know which authentication request to send to the device. This limitation does not apply to
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tokens enrolled via PKCS#11 — because tokens of this type may be identified immediately, before
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authentication.</para>
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</refsect1>
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<refsect1>
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<title>Options</title>
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<para>The following options are understood:</para>
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<variablelist>
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<varlistentry>
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<term><option>--password</option></term>
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<listitem><para>Enroll a regular password/passphrase. This command is mostly equivalent to
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<command>cryptsetup luksAddKey</command>, however may be combined with
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<option>--wipe-slot=</option> in one call, see below.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--recovery-key</option></term>
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<listitem><para>Enroll a recovery key. Recovery keys are mostly identical to passphrases, but are
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computer-generated instead of being chosen by a human, and thus have a guaranteed high entropy. The
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key uses a character set that is easy to type in, and may be scanned off screen via a QR code.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--pkcs11-token-uri=</option><replaceable>URI</replaceable></term>
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<listitem><para>Enroll a PKCS#11 security token or smartcard (e.g. a YubiKey). Expects a PKCS#11
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smartcard URI referring to the token. Alternatively the special value <literal>auto</literal> may
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be specified, in order to automatically determine the URI of a currently plugged in security token
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(of which there must be exactly one). The special value <literal>list</literal> may be used to
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enumerate all suitable PKCS#11 tokens currently plugged in. The security token must contain an RSA
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key pair which is used to encrypt the randomly generated key that is used to unlock the LUKS2
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volume. The encrypted key is then stored in the LUKS2 JSON token header area.</para>
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<para>In order to unlock a LUKS2 volume with an enrolled PKCS#11 security token, specify the
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<option>pkcs11-uri=</option> option in the respective <filename>/etc/crypttab</filename> line:</para>
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<programlisting>myvolume /dev/sda1 - pkcs11-uri=auto</programlisting>
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<para>See
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<citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum></citerefentry> for a
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more comprehensive example of a <command>systemd-cryptenroll</command> invocation and its matching
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<filename>/etc/crypttab</filename> line.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--fido2-device=</option><replaceable>PATH</replaceable></term>
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<listitem><para>Enroll a FIDO2 security token that implements the <literal>hmac-secret</literal>
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extension (e.g. a YubiKey). Expects a <filename>hidraw</filename> device referring to the FIDO2
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device (e.g. <filename>/dev/hidraw1</filename>). Alternatively the special value
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<literal>auto</literal> may be specified, in order to automatically determine the device node of a
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currently plugged in security token (of which there must be exactly one). The special value
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<literal>list</literal> may be used to enumerate all suitable FIDO2 tokens currently plugged in. Note
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that many hardware security tokens that implement FIDO2 also implement the older PKCS#11
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standard. Typically FIDO2 is preferable, given it's simpler to use and more modern.</para>
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<para>In order to unlock a LUKS2 volume with an enrolled FIDO2 security token, specify the
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<option>fido2-device=</option> option in the respective <filename>/etc/crypttab</filename> line:</para>
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<programlisting>myvolume /dev/sda1 - fido2-device=auto</programlisting>
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<para>See
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<citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum></citerefentry> for a
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more comprehensive example of a <command>systemd-cryptenroll</command> invocation and its matching
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<filename>/etc/crypttab</filename> line.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--fido2-with-client-pin=</option><replaceable>BOOL</replaceable></term>
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<listitem><para>When enrolling a FIDO2 security token, controls whether to require the user to enter
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a PIN when unlocking the volume (the FIDO2 <literal>clientPin</literal> feature). Defaults to
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<literal>yes</literal>. (Note: this setting is without effect if the security token does not support
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the <literal>clientPin</literal> feature at all, or does not allow enabling or disabling
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it.)</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--fido2-with-user-presence=</option><replaceable>BOOL</replaceable></term>
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<listitem><para>When enrolling a FIDO2 security token, controls whether to require the user to
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verify presence (tap the token, the FIDO2 <literal>up</literal> feature) when unlocking the volume.
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Defaults to <literal>yes</literal>. (Note: this setting is without effect if the security token does not support
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the <literal>up</literal> feature at all, or does not allow enabling or disabling it.)
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--fido2-with-user-verification=</option><replaceable>BOOL</replaceable></term>
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<listitem><para>When enrolling a FIDO2 security token, controls whether to require user verification
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when unlocking the volume (the FIDO2 <literal>uv</literal> feature). Defaults to
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<literal>no</literal>. (Note: this setting is without effect if the security token does not support
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the <literal>uv</literal> feature at all, or does not allow enabling or disabling it.)</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--tpm2-device=</option><replaceable>PATH</replaceable></term>
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<listitem><para>Enroll a TPM2 security chip. Expects a device node path referring to the TPM2 chip
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(e.g. <filename>/dev/tpmrm0</filename>). Alternatively the special value <literal>auto</literal> may
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be specified, in order to automatically determine the device node of a currently discovered TPM2
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device (of which there must be exactly one). The special value <literal>list</literal> may be used to
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enumerate all suitable TPM2 devices currently discovered.</para>
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<para>In order to unlock a LUKS2 volume with an enrolled TPM2 security chip, specify the
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<option>tpm2-device=</option> option in the respective <filename>/etc/crypttab</filename> line:</para>
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<programlisting>myvolume /dev/sda1 - tpm2-device=auto</programlisting>
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<para>See
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<citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum></citerefentry> for a
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more comprehensive example of a <command>systemd-cryptenroll</command> invocation and its matching
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<filename>/etc/crypttab</filename> line.</para>
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<para>Use <option>--tpm2-pcrs=</option> (see below) to configure which TPM2 PCR indexes to bind the
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enrollment to.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--tpm2-pcrs=</option><arg rep="repeat">PCR</arg></term>
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<listitem><para>Configures the TPM2 PCRs (Platform Configuration Registers) to bind the enrollment
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requested via <option>--tpm2-device=</option> to. Takes a <literal>+</literal> separated list of
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numeric PCR indexes in the range 0…23. If not used, defaults to PCR 7 only. If an empty string is
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specified, binds the enrollment to no PCRs at all. PCRs allow binding the enrollment to specific
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software versions and system state, so that the enrolled unlocking key is only accessible (may be
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"unsealed") if specific trusted software and/or configuration is used.</para>
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<table>
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<title>Well-known PCR Definitions</title>
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<!-- See: https://trustedcomputinggroup.org/resource/pc-client-specific-platform-firmware-profile-specification/ -->
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<!-- See: https://github.com/rhboot/shim/blob/main/README.tpm -->
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<!-- See: https://www.gnu.org/software/grub/manual/grub/html_node/Measured-Boot.html -->
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<!-- See: https://sourceforge.net/p/linux-ima/wiki/Home/ -->
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<tgroup cols='2' align='left' colsep='1' rowsep='1'>
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<colspec colname="pcr" />
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<colspec colname="definition" />
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<thead>
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<row>
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<entry>PCR</entry>
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<entry>Explanation</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>0</entry>
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<entry>Core system firmware executable code; changes on firmware updates</entry>
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</row>
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<row>
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<entry>1</entry>
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<entry>Core system firmware data/host platform configuration; typically contains serial and model numbers, changes on basic hardware/CPU/RAM replacements</entry>
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</row>
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<row>
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<entry>2</entry>
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<entry>Extended or pluggable executable code; includes option ROMs on pluggable hardware</entry>
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</row>
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<row>
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<entry>3</entry>
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<entry>Extended or pluggable firmware data; includes information about pluggable hardware</entry>
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</row>
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<row>
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<entry>4</entry>
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<entry>Boot loader; changes on boot loader updates. The shim project will measure the PE binary it chain loads into this PCR.</entry>
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</row>
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<row>
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<entry>5</entry>
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<entry>GPT/Partition table; changes when the partitions are added, modified or removed</entry>
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</row>
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<row>
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<entry>6</entry>
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<entry>Power state events; changes on system suspend/sleep</entry>
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</row>
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<row>
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<entry>7</entry>
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<entry>Secure boot state; changes when UEFI SecureBoot mode is enabled/disabled, or firmware certificates (PK, KEK, db, dbx, …) changes. The shim project will measure most of its (non-MOK) certificates and SBAT data into this PCR.</entry>
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</row>
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<row>
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<entry>8</entry>
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<entry><citerefentry><refentrytitle>sd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry> measures the kernel command line into this PCR.</entry>
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<!-- Grub measures all its commands and the kernel command line into PCR 8 too… -->
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</row>
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<!-- Grub measures all files it reads (including kernel image, initrd, …) into PCR 9… -->
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<row>
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<entry>10</entry>
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<entry>The IMA project measures its runtime state into this PCR.</entry>
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</row>
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<row>
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<entry>14</entry>
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<entry>The shim project measures its "MOK" certificates and hashes into this PCR.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>For most applications it should be sufficient to bind against PCR 7 (and possibly PCR 14, if
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shim/MOK is desired), as this includes measurements of the trusted certificates (and possibly hashes)
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that are used to validate all components of the boot process up to and including the OS kernel. In
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order to simplify firmware and OS version updates it's typically not advisable to include PCRs such
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as 0 and 2 in the binding of the enrollment, since the program code they cover should already be
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protected indirectly through the certificates measured into PCR 7. Validation through these
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certificates is typically preferable over validation through direct measurements as it is less
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brittle in context of OS/firmware updates: the measurements will change on every update, but code
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signatures likely will validate against pre-existing certificates.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--wipe-slot=</option><arg rep="repeat">SLOT</arg></term>
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<listitem><para>Wipes one or more LUKS2 key slots. Takes a comma separated list of numeric slot
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indexes, or the special strings <literal>all</literal> (for wiping all key slots),
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<literal>empty</literal> (for wiping all key slots that are unlocked by an empty passphrase),
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<literal>password</literal> (for wiping all key slots that are unlocked by a traditional passphrase),
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<literal>recovery</literal> (for wiping all key slots that are unlocked by a recovery key),
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<literal>pkcs11</literal> (for wiping all key slots that are unlocked by a PKCS#11 token),
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<literal>fido2</literal> (for wiping all key slots that are unlocked by a FIDO2 token),
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<literal>tpm2</literal> (for wiping all key slots that are unlocked by a TPM2 chip), or any
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combination of these strings or numeric indexes, in which case all slots matching either are
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wiped. As safety precaution an operation that wipes all slots without exception (so that the volume
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cannot be unlocked at all anymore, unless the volume key is known) is refused.</para>
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<para>This switch may be used alone, in which case only the requested wipe operation is executed. It
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may also be used in combination with any of the enrollment options listed above, in which case the
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enrollment is completed first, and only when successful the wipe operation executed — and the newly
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added slot is always excluded from the wiping. Combining enrollment and slot wiping may thus be used to
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update existing enrollments:</para>
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<programlisting>systemd-cryptenroll /dev/sda1 --wipe-slot=tpm2 --tpm2-device=auto</programlisting>
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<para>The above command will enroll the TPM2 chip, and then wipe all previously created TPM2
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enrollments on the LUKS2 volume, leaving only the newly created one. Combining wiping and enrollment
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may also be used to replace enrollments of different types, for example for changing from a PKCS#11
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enrollment to a FIDO2 one:</para>
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<programlisting>systemd-cryptenroll /dev/sda1 --wipe-slot=pkcs11 --fido2-device=auto</programlisting>
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<para>Or for replacing an enrolled empty password by TPM2:</para>
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<programlisting>systemd-cryptenroll /dev/sda1 --wipe-slot=empty --tpm2-device=auto</programlisting>
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</listitem>
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</varlistentry>
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<xi:include href="standard-options.xml" xpointer="help" />
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<xi:include href="standard-options.xml" xpointer="version" />
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Exit status</title>
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<para>On success, 0 is returned, a non-zero failure code otherwise.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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