diff -up shadow-4.8.1/lib/getdef.c.login_defs_HMAC_CRYPTO_ALGO shadow-4.8.1/lib/getdef.c
--- shadow-4.8.1/lib/getdef.c.login_defs_HMAC_CRYPTO_ALGO	2021-06-24 15:55:32.960558932 +0200
+++ shadow-4.8.1/lib/getdef.c	2021-06-24 15:55:32.975559187 +0200
@@ -61,6 +61,7 @@ struct itemdef {
 	{"ENV_TZ", NULL},			\
 	{"FAILLOG_ENAB", NULL},			\
 	{"FTMP_FILE", NULL},			\
+	{"HMAC_CRYPTO_ALGO", NULL},		\
 	{"ISSUE_FILE", NULL},			\
 	{"LASTLOG_ENAB", NULL},			\
 	{"LOGIN_STRING", NULL},			\
diff -up shadow-4.8.1/man/login.defs.5.xml.login_defs_HMAC_CRYPTO_ALGO shadow-4.8.1/man/login.defs.5.xml
--- shadow-4.8.1/man/login.defs.5.xml.login_defs_HMAC_CRYPTO_ALGO	2021-06-24 15:55:32.929558405 +0200
+++ shadow-4.8.1/man/login.defs.5.xml	2021-06-24 15:55:32.975559187 +0200
@@ -50,6 +50,7 @@
 <!ENTITY FAKE_SHELL            SYSTEM "login.defs.d/FAKE_SHELL.xml">
 <!ENTITY FTMP_FILE             SYSTEM "login.defs.d/FTMP_FILE.xml">
 <!ENTITY GID_MAX               SYSTEM "login.defs.d/GID_MAX.xml">
+<!ENTITY HMAC_CRYPTO_ALGO      SYSTEM "login.defs.d/HMAC_CRYPTO_ALGO.xml">
 <!ENTITY HOME_MODE             SYSTEM "login.defs.d/HOME_MODE.xml">
 <!ENTITY HUSHLOGIN_FILE        SYSTEM "login.defs.d/HUSHLOGIN_FILE.xml">
 <!ENTITY ISSUE_FILE            SYSTEM "login.defs.d/ISSUE_FILE.xml">
@@ -197,6 +198,7 @@
       &FAKE_SHELL;
       &FTMP_FILE;
       &GID_MAX; <!-- documents also GID_MIN -->
+      &HMAC_CRYPTO_ALGO;
       &HOME_MODE;
       &HUSHLOGIN_FILE;
       &ISSUE_FILE;
diff -up shadow-4.8.1/man/login.defs.d/HMAC_CRYPTO_ALGO.xml.login_defs_HMAC_CRYPTO_ALGO shadow-4.8.1/man/login.defs.d/HMAC_CRYPTO_ALGO.xml
--- shadow-4.8.1/man/login.defs.d/HMAC_CRYPTO_ALGO.xml.login_defs_HMAC_CRYPTO_ALGO	2021-06-24 15:55:32.975559187 +0200
+++ shadow-4.8.1/man/login.defs.d/HMAC_CRYPTO_ALGO.xml	2021-06-24 15:55:32.975559187 +0200
@@ -0,0 +1,44 @@
+<!--
+   Copyright (c) 1991 - 1993, Julianne Frances Haugh
+   Copyright (c) 1991 - 1993, Chip Rosenthal
+   Copyright (c) 2007 - 2008, Nicolas François
+   All rights reserved.
+
+   Redistribution and use in source and binary forms, with or without
+   modification, are permitted provided that the following conditions
+   are met:
+   1. Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+   2. Redistributions in binary form must reproduce the above copyright
+      notice, this list of conditions and the following disclaimer in the
+      documentation and/or other materials provided with the distribution.
+   3. The name of the copyright holders or contributors may not be used to
+      endorse or promote products derived from this software without
+      specific prior written permission.
+
+   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+   PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT
+   HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+-->
+<varlistentry condition="no_pam">
+  <term><option>HMAC_CRYPTO_ALGO</option> (string)</term>
+  <listitem>
+    <para>
+      Used to select the HMAC cryptography algorithm that the pam_timestamp
+      module is going to use to calculate the keyed-hash message authentication
+      code.
+    </para>
+    <para>
+      Note: Check <refentrytitle>hmac</refentrytitle><manvolnum>3</manvolnum>
+      to see the possible algorithms that are available in your system.
+    </para>
+  </listitem>
+</varlistentry>
diff -up shadow-4.8.1/man/Makefile.am.login_defs_HMAC_CRYPTO_ALGO shadow-4.8.1/man/Makefile.am
--- shadow-4.8.1/man/Makefile.am.login_defs_HMAC_CRYPTO_ALGO	2021-06-24 15:55:32.975559187 +0200
+++ shadow-4.8.1/man/Makefile.am	2021-06-24 15:57:11.231229970 +0200
@@ -136,6 +136,7 @@ login_defs_v = \
 	FAKE_SHELL.xml \
 	FTMP_FILE.xml \
 	GID_MAX.xml \
+	HMAC_CRYPTO_ALGO.xml \
 	HUSHLOGIN_FILE.xml \
 	ISSUE_FILE.xml \
 	KILLCHAR.xml \