<refnamediv>
<refname>sd_id128_get_machine</refname>
+ <refname>sd_id128_get_machine_app_specific</refname>
<refname>sd_id128_get_boot</refname>
<refname>sd_id128_get_invocation</refname>
<refpurpose>Retrieve 128-bit IDs</refpurpose>
<paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
</funcprototype>
+ <funcprototype>
+ <funcdef>int <function>sd_id128_get_machine_app_specific</function></funcdef>
+ <paramdef>sd_id128_t <parameter>app_id</parameter></paramdef>
+ <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
+ </funcprototype>
+
<funcprototype>
<funcdef>int <function>sd_id128_get_boot</function></funcdef>
<paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
<refsect1>
<title>Description</title>
- <para><function>sd_id128_get_machine()</function> returns the
- machine ID of the executing host. This reads and parses the
- <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
- file. This function caches the machine ID internally to make
- retrieving the machine ID a cheap operation.</para>
+ <para><function>sd_id128_get_machine()</function> returns the machine ID of the executing host. This reads and
+ parses the <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ file. This function caches the machine ID internally to make retrieving the machine ID a cheap operation. This ID
+ may be used wherever a unique identifier for the local system is needed. However, it is recommended to use this ID
+ as-is only in trusted environments. In untrusted environments it is recommended to derive an application specific
+ ID from this machine ID, in an irreversable (cryptographically secure) way. To make this easy
+ <function>sd_id128_get_machine_app_specific()</function> is provided, see below.</para>
+
+ <para><function>sd_id128_get_machine_app_specific()</function> is similar to
+ <function>sd_id128_get_machine()</function>, but retrieves a machine ID that is specific to the application that is
+ identified by the indicated application ID. It is recommended to use this function instead of
+ <function>sd_id128_get_machine()</function> when passing an ID to untrusted environments, in order to make sure
+ that the original machine ID may not be determined externally. The application-specific ID should be generated via
+ a tool like <command>journalctl --new-id128</command>, and may be compiled into the application. This function will
+ return the same application-specific ID for each combination of machine ID and application ID. Internally, this
+ function calculates HMAC-SHA256 of the application ID, keyed by the machine ID.</para>
<para><function>sd_id128_get_boot()</function> returns the boot ID
of the executing kernel. This reads and parses the
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The
ID is cached internally. In future a different mechanism to determine the invocation ID may be added.</para>
- <para>Note that <function>sd_id128_get_boot()</function> and <function>sd_id128_get_invocation()</function> always
- return UUID v4 compatible IDs. <function>sd_id128_get_machine()</function> will also return a UUID v4-compatible
- ID on new installations but might not on older. It is possible to convert the machine ID into a UUID v4-compatible
- one. For more information, see
+ <para>Note that <function>sd_id128_get_machine_app_specific()</function>, <function>sd_id128_get_boot()</function>
+ and <function>sd_id128_get_invocation()</function> always return UUID v4 compatible IDs.
+ <function>sd_id128_get_machine()</function> will also return a UUID v4-compatible ID on new installations but might
+ not on older. It is possible to convert the machine ID into a UUID v4-compatible one. For more information, see
<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
<para>For more information about the <literal>sd_id128_t</literal>
<refsect1>
<title>Notes</title>
- <para>The <function>sd_id128_get_machine()</function>, <function>sd_id128_get_boot()</function> and
- <function>sd_id128_get_invocation()</function> interfaces are available as a shared library, which can be compiled
- and linked to with the <literal>libsystemd</literal> <citerefentry
+ <para>The <function>sd_id128_get_machine()</function>, <function>sd_id128_get_machine_app_specific()</function>
+ <function>sd_id128_get_boot()</function> and <function>sd_id128_get_invocation()</function> interfaces are
+ available as a shared library, which can be compiled and linked to with the
+ <literal>libsystemd</literal> <citerefentry
project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
</refsect1>
+ <refsect1>
+ <title>Examples</title>
+
+ <example>
+ <title>Application-specific machine ID</title>
+
+ <para>Here's a simple example for an application specific machine ID:</para>
+
+ <programlisting>#include <systemd/sd-id128.h>
+#include <stdio.h>
+
+#define OUR_APPLICATION_ID SD_ID128_MAKE(c2,73,27,73,23,db,45,4e,a6,3b,b9,6e,79,b5,3e,97)
+
+int main(int argc, char *argv[]) {
+ sd_id128_t id;
+ sd_id128_get_machine_app_specific(OUR_APPLICATION_ID, &id);
+ printf("Our application ID: " SD_ID128_FORMAT_STR "\n", SD_ID128_FORMAT_VAL(id));
+ return 0;
+}</programlisting>
+ </example>
+ </refsect1>
+
<refsect1>
<title>See Also</title>
~ianmdlvl / elogind.git / blobdiff