tzpfms/zfs-fido2-change-key.8.html
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<title>ZFS-FIDO2-CHANGE-KEY(8)</title>
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<table class="head">
<tr>
<td class="head-ltitle">ZFS-FIDO2-CHANGE-KEY(8)</td>
<td class="head-vol">System Manager's Manual</td>
<td class="head-rtitle">ZFS-FIDO2-CHANGE-KEY(8)</td>
</tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp"><code class="Nm">zfs-fido2-change-key</code> &#x2014;
<span class="Nd">change ZFS dataset key to one authenticated by a FIDO2
device</span></p>
</section>
<section class="Sh">
<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1>
<table class="Nm">
<tr>
<td><code class="Nm">zfs-fido2-change-key</code></td>
<td>[<code class="Fl">-b</code> <var class="Ar">backup-file</var>]
<var class="Ar">dataset</var></td>
</tr>
</table>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp">To normalise the <var class="Ar">dataset</var>,
<code class="Nm">zfs-fido2-change-key</code> will open its encryption root
in its stead. <code class="Nm">zfs-fido2-change-key</code> will
<a class="permalink" href="#never"><i class="Em" id="never">never</i></a>
create or destroy encryption roots; use
<a class="Xr" href="https://manpages.debian.org/bookworm/zfs-change-key.8">zfs-change-key(8)</a>
for that.</p>
<p class="Pp">First, a connection is made to the FIDO2 device, which
<i class="Em">must</i> support the
&#x2018;<code class="Li">hmac-secret</code>&#x2019; extension.</p>
<p class="Pp">If <var class="Ar">dataset</var> was previously encrypted with
<code class="Nm">fzifdso</code> and the <b class="Sy">FIDO2</b> back-end was
used, previous credentials will be deleted from their devices (as-if via
<a class="Xr" href="zfs-fido2-clear-key.8.html">zfs-fido2-clear-key(8)</a>),
if available. Otherwise, or in case of an error, data required for manual
intervention will be written to the standard error stream.</p>
<p class="Pp">Next, a new credential of type ES256 is generated on the device
(with relying party ID <code class="Li">fzifdso</code> and name equal to the
dataset name) with the &#x2018;<code class="Li">hmac-secret</code>&#x2019;
extension requested; the device PIN, if any, is prompted for here. This
mimicks a WebAuthn registration step.</p>
<p class="Pp">Then, the credential is asserted with a 32-byte random salt, which
hashes it with device-private data, and thus generates the wrapping key
(which is optionally backed up (see
<a class="Sx" href="#OPTIONS">OPTIONS</a>)). This mimicks a WebAuthn login
step.</p>
<p class="Pp">The following properties are set on
<var class="Ar">dataset</var>:</p>
<ul class="Bl-bullet Bd-indent Bl-compact">
<li id="xyz.nabijaczleweli:tzpfms.backend"><a class="permalink" href="#xyz.nabijaczleweli:tzpfms.backend"><code class="Li">xyz.nabijaczleweli:tzpfms.backend</code></a>=<b class="Sy">FIDO2</b></li>
<li id="xyz.nabijaczleweli:tzpfms.key"><a class="permalink" href="#xyz.nabijaczleweli:tzpfms.key"><code class="Li">xyz.nabijaczleweli:tzpfms.key</code></a>=<var class="Ar">salt</var><code class="Cm">:</code><var class="Ar">credential-ID</var><code class="Cm">:</code><var class="Ar">credential-public-key</var>[<code class="Cm">.</code>&#x2026;]&#x2026;</li>
</ul>
<p class="Pp"><code class="Li">tzpfms.backend</code> identifies this dataset for
work with <b class="Sy">FIDO2</b>-back-ended <code class="Nm">tzpfms</code>
tools (i.e. <code class="Nm">fzifdso</code>
<a class="Xr" href="zfs-fido2-change-key.8.html">zfs-fido2-change-key(8)</a>,
<a class="Xr" href="zfs-fido2-load-key.8.html">zfs-fido2-load-key(8)</a>,
<a class="Xr" href="zfs-fido2-add-backup.8.html">zfs-fido2-add-backup(8)</a>,
and
<a class="Xr" href="zfs-fido2-clear-key.8.html">zfs-fido2-clear-key(8)</a>).</p>
<p class="Pp"><code class="Li">tzpfms.key</code> is a colon-separated tuple of
unpadded URL-safe base64 blobs; the first one is the random salt; the second
represents the ID of created credential, and the third &#x2013; its public
key. There exists no other user-land tool for deciphering this; perhaps
there should be.</p>
<p class="Pp">Finally, the equivalent of <code class="Nm">zfs</code>
<code class="Cm">change-key</code> <code class="Fl">-o</code>
<code class="Li">keylocation=prompt</code> <code class="Fl">-o</code>
<code class="Li">keyformat=raw</code> <var class="Ar">dataset</var> is
performed with the new key. If an error occurred, best effort is made to
clean up the properties, or to issue a note for manual intervention into the
standard error stream.</p>
<p class="Pp">A final verification should be made by running
<code class="Nm">zfs-fido2-load-key</code> <code class="Fl">-n</code>
<var class="Ar">dataset</var>. If that command succeeds, all is well, but
otherwise the dataset can be manually rolled back to a passphrase with
<code class="Nm">zfs-fido2-clear-key</code> <var class="Ar">dataset</var>
(or, if that fails to work, <code class="Nm">zfs</code>
<code class="Cm">change-key</code> <code class="Fl">-o</code>
<code class="Li">keyformat=passphrase</code> <var class="Ar">dataset</var>),
and you are hereby asked to report a bug, please.</p>
<p class="Pp"><code class="Nm">zfs-fido2-clear-key</code>
<var class="Ar">dataset</var> can be used to clear the properties and go
back to using a passphrase.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="OPTIONS"><a class="permalink" href="#OPTIONS">OPTIONS</a></h1>
<dl class="Bl-tag Bl-compact">
<dt id="b"><a class="permalink" href="#b"><code class="Fl">-b</code></a>
<var class="Ar">backup-file</var></dt>
<dd>Save a back-up of the key to <var class="Ar">backup-file</var>, which must
not exist beforehand. This back-up <i class="Em">must</i> be stored
securely, off-site. In case of a catastrophic event, the key can be loaded
by running
<div class="Bd Bd-indent"><code class="Li"><code class="Nm">zfs</code>
<code class="Cm">load-key</code> <var class="Ar">dataset</var>
<code class="Li">&lt;</code>
<var class="Ar">backup-file</var></code></div>
</dd>
</dl>
</section>
<section class="Sh">
<h1 class="Sh" id="ENVIRONMENT_VARIABLES"><a class="permalink" href="#ENVIRONMENT_VARIABLES">ENVIRONMENT
VARIABLES</a></h1>
<dl class="Bl-tag Bl-compact">
<dt id="TZPFMS_PASSPHRASE_HELPER"><a class="permalink" href="#TZPFMS_PASSPHRASE_HELPER"><code class="Ev">TZPFMS_PASSPHRASE_HELPER</code></a></dt>
<dd>By default, passphrases are prompted for and read in on the standard
output and input streams. If
<code class="Ev">TZPFMS_PASSPHRASE_HELPER</code> is set and nonempty, it
will be run via <span class="Pa">/bin/</span><code class="Nm">sh</code>
<code class="Fl">-c</code> to provide each passphrase, instead.
<p class="Pp">The standard output stream of the helper is tied to an
anonymous file and used in its entirety as the passphrase, except for a
trailing new-line, if any. The arguments are:</p>
<div class="Bd-indent">
<dl class="Bl-tag Bl-compact">
<dt id="$1"><a class="permalink" href="#$1"><code class="Li">$1</code></a></dt>
<dd>Pre-formatted noun phrase with all the information below, for use as a
prompt</dd>
<dt id="$2"><a class="permalink" href="#$2"><code class="Li">$2</code></a></dt>
<dd>Either the dataset name or the device feature being prompted for</dd>
<dt id="$3"><a class="permalink" href="#$3"><code class="Li">$3</code></a></dt>
<dd>&quot;new&quot; if this is for a new passphrase, otherwise blank</dd>
<dt id="$4"><a class="permalink" href="#$4"><code class="Li">$4</code></a></dt>
<dd>&quot;again&quot; if it's the second prompt for that passphrase,
otherwise blank</dd>
</dl>
</div>
<p class="Pp" id="127">If the helper doesn't exist (the shell exits with
<a class="permalink" href="#127"><b class="Sy">127</b></a>), a
diagnostic is issued and the normal prompt is used as fall-back. If it
fails for any other reason, the prompting is aborted.</p>
</dd>
</dl>
</section>
<section class="Sh">
<h1 class="Sh" id="FIDO2_back-end_configuration"><a class="permalink" href="#FIDO2_back-end_configuration">FIDO2
back-end configuration</a></h1>
<section class="Ss">
<h2 class="Ss" id="Environment_variables"><a class="permalink" href="#Environment_variables">Environment
variables</a></h2>
<dl class="Bl-tag Bl-compact">
<dt id="FIDO_DEBUG"><a class="permalink" href="#FIDO_DEBUG"><code class="Ev">FIDO_DEBUG</code></a></dt>
<dd>If set, enables libfido2 debug logging to the standard error stream.</dd>
</dl>
</section>
<section class="Ss">
<h2 class="Ss" id="Device_selection"><a class="permalink" href="#Device_selection">Device
selection</a></h2>
<p class="Pp">When creating, the first device which supports the
&#x2018;<code class="Li">hmac-secret</code>&#x2019; extension is used. When
loading, the assertion yielding the key is shopped around to every such
device.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="See_also"><a class="permalink" href="#See_also">See
also</a></h2>
<p class="Pp">The libfido2 documentation at
<a class="Lk" href="https://developers.yubico.com/libfido2/">https://developers.yubico.com/libfido2/</a>.</p>
</section>
</section>
<section class="Sh">
<h1 class="Sh" id="SPECIAL_THANKS"><a class="permalink" href="#SPECIAL_THANKS">SPECIAL
THANKS</a></h1>
<p class="Pp">To all who support further development, in particular:</p>
<ul class="Bl-bullet Bd-indent Bl-compact">
<li>ThePhD</li>
<li>Embark Studios</li>
<li>Jasper Bekkers</li>
<li>EvModder</li>
</ul>
</section>
<section class="Sh">
<h1 class="Sh" id="REPORTING_BUGS"><a class="permalink" href="#REPORTING_BUGS">REPORTING
BUGS</a></h1>
<p class="Pp"><a class="Lk" href="https://todo.sr.ht/~nabijaczleweli/fzifdso">https://todo.sr.ht/~nabijaczleweli/fzifdso</a></p>
<p class="Pp"><a class="Mt" href="mailto:~nabijaczleweli/tzpfms@lists.sr.ht">~nabijaczleweli/tzpfms@lists.sr.ht</a>,
archived at
<a class="Lk" href="https://lists.sr.ht/~nabijaczleweli/tzpfms">https://lists.sr.ht/~nabijaczleweli/tzpfms</a>.</p>
</section>
</div>
<table class="foot">
<tr>
<td class="foot-date">March 4, 2024</td>
<td class="foot-os">fzifdso 0.4.1</td>
</tr>
</table>
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