samples: net: sockets: coap_server: Add CoAP secure support

Update the CoAP server sample to demonstrate using DTLS for secure
sockets.

Signed-off-by: Pieter De Gendt <pieter.degendt@basalte.be>

samples/net/sockets/coap_server/CMakeLists.txt

@@ -4,6 +4,19 @@ cmake_minimum_required(VERSION 3.20.0)
 find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
 project(coap_server)
 
+if(CONFIG_NET_SOCKETS_ENABLE_DTLS AND
+   CONFIG_MBEDTLS_KEY_EXCHANGE_PSK_ENABLED AND
+   (CONFIG_NET_SAMPLE_PSK_HEADER_FILE STREQUAL "dummy_psk.h"))
+  add_custom_target(development_psk
+    COMMAND ${CMAKE_COMMAND} -E echo "----------------------------------------------------------"
+    COMMAND ${CMAKE_COMMAND} -E echo "--- WARNING: Using dummy PSK! Only suitable for        ---"
+    COMMAND ${CMAKE_COMMAND} -E echo "--- development. Set NET_SAMPLE_PSK_HEADER_FILE to use ---"
+    COMMAND ${CMAKE_COMMAND} -E echo "--- own pre-shared key.                                ---"
+    COMMAND ${CMAKE_COMMAND} -E echo "----------------------------------------------------------"
+  )
+  add_dependencies(app development_psk)
+endif()
+
 FILE(GLOB app_sources src/*.c)
 target_sources(app PRIVATE ${app_sources})
 target_include_directories(app PRIVATE ${ZEPHYR_BASE}/subsys/net/ip)
@@ -18,3 +31,19 @@ zephyr_iterable_section(
   SUBALIGN ${CONFIG_LINKER_ITERABLE_SUBALIGN})
 
 include(${ZEPHYR_BASE}/samples/net/common/common.cmake)
+
+set(gen_dir ${ZEPHYR_BINARY_DIR}/include/generated/)
+
+foreach(inc_file
+	ca.der
+	server.der
+	server_privkey.der
+	coaps-server-cert.der
+	coaps-server-key.der
+)
+  generate_inc_file_for_target(
+    app
+    src/certs/${inc_file}
+    ${gen_dir}/${inc_file}.inc
+  )
+endforeach()

samples/net/sockets/coap_server/Kconfig

@@ -0,0 +1,36 @@
+# Copyright (c) 2023, Emna Rekik
+# Copyright (c) 2025, Basalte bv
+# SPDX-License-Identifier: Apache-2.0
+
+# Config options for CoAP server sample application
+
+mainmenu "CoAP server sample application"
+
+config NET_SAMPLE_COAPS_SERVICE
+	bool "Enable CoAP secure service"
+	depends on NET_SOCKETS_ENABLE_DTLS || TLS_CREDENTIALS
+
+config NET_SAMPLE_COAP_SERVER_SERVICE_PORT
+	int "Port number for CoAP service"
+	default 5684 if NET_SAMPLE_COAPS_SERVICE
+	default 5683
+
+if NET_SAMPLE_COAPS_SERVICE
+
+config NET_SAMPLE_PSK_HEADER_FILE
+	string "Header file containing PSK"
+	default "dummy_psk.h"
+	depends on MBEDTLS_KEY_EXCHANGE_PSK_ENABLED
+	help
+	  Name of a header file containing a pre-shared key.
+
+config NET_SAMPLE_CERTS_WITH_SC
+	bool "Signed Certificates"
+	depends on NET_SOCKETS_SOCKOPT_TLS
+	help
+	  Enable this flag, if you are interested to run this
+	  application with certificates.
+
+endif
+
+source "Kconfig.zephyr"

samples/net/sockets/coap_server/README.rst

@@ -17,8 +17,9 @@ service's name. A linker file is required, see ``sections-ram.ld`` for an exampl
 This demo assumes that the platform of choice has networking support,
 some adjustments to the configuration may be needed.
 
-The sample will listen for requests in the CoAP UDP port (5683) in the
-site-local IPv6 multicast address reserved for CoAP nodes.
+The sample will listen for requests on the default CoAP UDP port
+(5683 or 5684 for secure CoAP) in the site-local IPv6 multicast address reserved
+for CoAP nodes.
 
 The sample exports the following resources:
 
@@ -37,6 +38,16 @@ against coap-server.
 
 Building And Running
 ********************
+Build the CoAP server sample application like this:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/net/sockets/coap_server
+   :board: <board to use>
+   :goals: build
+   :compact:
+
+Use :zephyr_file:`overlay-dtls.conf <samples/net/sockets/coap_server/overlay-dtls.conf>`
+to build the sample with CoAP secure resources instead.
 
 This project has no output in case of success, the correct
 functionality can be verified by using some external tool such as tcpdump

samples/net/sockets/coap_server/overlay-dtls.conf

@@ -0,0 +1,18 @@
+CONFIG_NET_SAMPLE_COAPS_SERVICE=y
+
+# Secure Socket
+CONFIG_NET_SOCKETS_SOCKOPT_TLS=y
+CONFIG_NET_SOCKETS_ENABLE_DTLS=y
+CONFIG_NET_SOCKETS_TLS_MAX_CLIENT_SESSION_COUNT=6
+CONFIG_NET_SOCKETS_TLS_MAX_CONTEXTS=6
+CONFIG_NET_SOCKETS_DTLS_TIMEOUT=30000
+
+# TLS configuration
+CONFIG_MBEDTLS_DEBUG=y
+CONFIG_MBEDTLS=y
+CONFIG_MBEDTLS_BUILTIN=y
+CONFIG_MBEDTLS_ENABLE_HEAP=y
+CONFIG_MBEDTLS_HEAP_SIZE=60000
+CONFIG_MBEDTLS_SSL_DTLS_CONNECTION_ID=y
+CONFIG_MBEDTLS_SSL_MAX_CONTENT_LEN=2048
+CONFIG_MBEDTLS_KEY_EXCHANGE_PSK_ENABLED=y

samples/net/sockets/coap_server/prj.conf

@@ -6,7 +6,7 @@ CONFIG_NET_UDP=y
 # Socket
 CONFIG_NET_SOCKETS=y
 CONFIG_POSIX_API=y
-CONFIG_ZVFS_POLL_MAX=4
+CONFIG_ZVFS_POLL_MAX=10
 
 # CoAP
 CONFIG_COAP=y
@@ -48,3 +48,6 @@ CONFIG_NET_IF_MCAST_IPV6_ADDR_COUNT=5
 CONFIG_NET_IPV4=n
 CONFIG_NET_CONFIG_NEED_IPV4=n
 CONFIG_NET_CONFIG_MY_IPV4_ADDR="192.0.2.1"
+
+# Enable v4-mapped-on-v6
+CONFIG_NET_IPV4_MAPPING_TO_IPV6=y

samples/net/sockets/coap_server/sample.yaml

@@ -12,6 +12,16 @@ tests:
     platform_allow:
       - native_sim
       - qemu_x86
+  sample.net.sockets.coaps_server:
+    harness: net
+    extra_args: EXTRA_CONF_FILE="overlay-dtls.conf"
+    tags:
+      - net
+      - socket
+      - tls
+    platform_allow:
+      - native_sim
+      - qemu_x86
   sample.net.sockets.coap_server.wifi.nrf70dk:
     extra_args:
       - SNIPPET=wifi-ipv4

samples/net/sockets/coap_server/src/certificate.h

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2018 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef __CERTIFICATE_H__
+#define __CERTIFICATE_H__
+
+#define SERVER_CERTIFICATE_TAG 1
+#define PSK_TAG 2
+
+#if !defined(CONFIG_NET_SAMPLE_CERTS_WITH_SC)
+static const unsigned char server_certificate[] = {
+#include "coaps-server-cert.der.inc"
+};
+
+/* This is the private key in pkcs#8 format. */
+static const unsigned char private_key[] = {
+#include "coaps-server-key.der.inc"
+};
+
+#else
+
+static const unsigned char ca_certificate[] = {
+#include "ca.der.inc"
+};
+
+static const unsigned char server_certificate[] = {
+#include "server.der.inc"
+};
+
+/* This is the private key in pkcs#8 format. */
+static const unsigned char private_key[] = {
+#include "server_privkey.der.inc"
+};
+#endif
+
+#if defined(CONFIG_MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)
+#include CONFIG_NET_SAMPLE_PSK_HEADER_FILE
+#endif
+
+#endif /* __CERTIFICATE_H__ */

samples/net/sockets/coap_server/src/dummy_psk.h

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2019 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef __DUMMY_PSK_H__
+#define __DUMMY_PSK_H__
+
+static const unsigned char psk[] = {0x01, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06,
+0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f};
+static const char psk_id[] = "PSK_identity";
+
+#endif /* __DUMMY_PSK_H__ */

samples/net/sockets/coap_server/src/main.c

@@ -8,18 +8,98 @@
 LOG_MODULE_REGISTER(net_coap_service_sample, LOG_LEVEL_DBG);
 
 #include <zephyr/net/coap_service.h>
-#include <zephyr/net/mld.h>
+
+#include "net_sample_common.h"
 
 #ifdef CONFIG_NET_IPV6
+#include <zephyr/net/mld.h>
+
 #include "net_private.h"
 #include "ipv6.h"
 #endif
 
-#include "net_sample_common.h"
+static uint16_t coap_port = CONFIG_NET_SAMPLE_COAP_SERVER_SERVICE_PORT;
 
-static const uint16_t coap_port = 5683;
+#ifndef CONFIG_NET_SAMPLE_COAPS_SERVICE
 
-#ifdef CONFIG_NET_IPV6
+COAP_SERVICE_DEFINE(coap_server, NULL, &coap_port, COAP_SERVICE_AUTOSTART);
+
+#else /* CONFIG_NET_SAMPLE_COAPS_SERVICE */
+
+#include "certificate.h"
+
+static const sec_tag_t sec_tag_list_verify_none[] = {
+		SERVER_CERTIFICATE_TAG,
+#if defined(CONFIG_MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)
+		PSK_TAG,
+#endif
+};
+
+COAPS_SERVICE_DEFINE(coap_server, NULL, &coap_port, 0,
+		     sec_tag_list_verify_none, sizeof(sec_tag_list_verify_none));
+
+#endif /* CONFIG_NET_SAMPLE_COAPS_SERVICE */
+
+static int setup_dtls(void)
+{
+#if defined(CONFIG_NET_SAMPLE_COAPS_SERVICE)
+#if defined(CONFIG_NET_SOCKETS_ENABLE_DTLS)
+	int err;
+
+#if defined(CONFIG_NET_SAMPLE_CERTS_WITH_SC)
+	err = tls_credential_add(SERVER_CERTIFICATE_TAG,
+				 TLS_CREDENTIAL_CA_CERTIFICATE,
+				 ca_certificate,
+				 sizeof(ca_certificate));
+	if (err < 0) {
+		LOG_ERR("Failed to register CA certificate: %d", err);
+		return err;
+	}
+#endif /* defined(CONFIG_NET_SAMPLE_CERTS_WITH_SC) */
+
+	err = tls_credential_add(SERVER_CERTIFICATE_TAG,
+				 TLS_CREDENTIAL_SERVER_CERTIFICATE,
+				 server_certificate,
+				 sizeof(server_certificate));
+	if (err < 0) {
+		LOG_ERR("Failed to register public certificate: %d", err);
+		return err;
+	}
+
+	err = tls_credential_add(SERVER_CERTIFICATE_TAG,
+				 TLS_CREDENTIAL_PRIVATE_KEY,
+				 private_key, sizeof(private_key));
+	if (err < 0) {
+		LOG_ERR("Failed to register private key: %d", err);
+		return err;
+	}
+
+#if defined(CONFIG_MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)
+	err = tls_credential_add(PSK_TAG,
+				 TLS_CREDENTIAL_PSK,
+				 psk,
+				 sizeof(psk));
+	if (err < 0) {
+		LOG_ERR("Failed to register PSK: %d", err);
+		return err;
+	}
+
+	err = tls_credential_add(PSK_TAG,
+				 TLS_CREDENTIAL_PSK_ID,
+				 psk_id,
+				 sizeof(psk_id) - 1);
+	if (err < 0) {
+		LOG_ERR("Failed to register PSK ID: %d", err);
+		return err;
+	}
+
+#endif /* defined(CONFIG_MBEDTLS_KEY_EXCHANGE_PSK_ENABLED) */
+#endif /* defined(CONFIG_NET_SOCKETS_ENABLE_DTLS) */
+#endif /* defined(CONFIG_NET_SAMPLE_COAPS_SERVICE) */
+	return 0;
+}
+
+#if !defined(CONFIG_NET_SAMPLE_COAPS_SERVICE) && defined(CONFIG_NET_IPV6)
 
 #define ALL_NODES_LOCAL_COAP_MCAST \
 	{ { { 0xff, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xfd } } }
@@ -27,13 +107,13 @@ static const uint16_t coap_port = 5683;
 #define MY_IP6ADDR \
 	{ { { 0x20, 0x01, 0x0d, 0xb8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x1 } } }
 
-static int join_coap_multicast_group(void)
+static int join_coap_multicast_group(uint16_t port)
 {
 	static struct in6_addr my_addr = MY_IP6ADDR;
-	static struct sockaddr_in6 mcast_addr = {
+	struct sockaddr_in6 mcast_addr = {
 		.sin6_family = AF_INET6,
 		.sin6_addr = ALL_NODES_LOCAL_COAP_MCAST,
-		.sin6_port = htons(coap_port) };
+		.sin6_port = htons(port) };
 	struct net_if_addr *ifaddr;
 	struct net_if *iface;
 	int ret;
@@ -71,22 +151,36 @@ static int join_coap_multicast_group(void)
 	return 0;
 }
 
+#endif /* CONFIG_NET_IPV6 */
+
 int main(void)
 {
+	int ret;
+
 	wait_for_network();
 
-	return join_coap_multicast_group();
+	ret = setup_dtls();
+	if (ret < 0) {
+		LOG_ERR("Failed to setup DTLS (%d)", ret);
+		return ret;
 	}
 
-#else /* CONFIG_NET_IPV6 */
-
-int main(void)
-{
-	wait_for_network();
-
-	return 0;
+#if !defined(CONFIG_NET_SAMPLE_COAPS_SERVICE) && defined(CONFIG_NET_IPV6)
+	ret = join_coap_multicast_group(coap_port);
+	if (ret < 0) {
+		LOG_ERR("Failed to join CoAP all-nodes multicast (%d)", ret);
+		return ret;
 	}
+#endif
 
-#endif /* CONFIG_NET_IPV6 */
+#ifdef CONFIG_NET_SAMPLE_COAPS_SERVICE
+	/* CoAP secure server has to be started manually after DTLS setup */
+	ret = coap_service_start(&coap_server);
+	if (ret < 0) {
+		LOG_ERR("Failed to start CoAP secure server (%d)", ret);
+		return ret;
+	}
+#endif
 
-COAP_SERVICE_DEFINE(coap_server, NULL, &coap_port, COAP_SERVICE_AUTOSTART);
+	return ret;
+}