CoAP with DTLS 1.2 on download sample

[Harvey Zheng]

hi,

I use download sample on nRF9160DK. I try to use CoAP with DTLS, but the SAMPLE_FILE_URL only support http and https url, I can't find another coaps server to replace it. How can I use CoAP with DTLS on download sample?

[JONATHAN LL]

Hello,
You need to set SAMPLE_FILE_CUSTOM to specify a custom server, and enable CONFIG_COAP for COAP to work, And change the cert_provision function to write a PSK rather than a CA chain.

So set up a CoAPs server, set CONFIG_SAMPLE_FILE_URL to point to your CoAPs server.
SAMPLE_FILE_URL supports all possible types of servers (it is just a string), but we only have defaults for HTTP and HTTPS. So you need to set up one for yourself.

Regards,
Jonathan

[Harvey Zheng]

Hi,

I use NCS 2.0 and 9160modem V1.3.2. Imodified it according to your idea, but still fail. In the code I need to add the following code, I don't known what else I need to add.

nrf_sec_cipher_t cipher_list[] = { 0xC0A8 };
err = setsockopt(dl->fd, SOL_TLS, TLS_CIPHERSUITE_LIST, cipher_list, sizeof(cipher_list));
if (err) {
    /* Failed to set up cipher suite list. */
    goto cleanup;
}

static int cert_provision(void)
{
	int err;
	bool exists;

    /*----------- PSK -----------------*/
    err = modem_key_mgmt_exists(SEC_TAG,
				    MODEM_KEY_MGMT_CRED_TYPE_PSK,
				    &exists);
	if (err) {
		printk("Failed to check for certificates err %d\n", err);
		return err;
	}

	if (exists) {
		printk("PSK ");
		/* Let's compare the existing credential */
		err = modem_key_mgmt_cmp(SEC_TAG,
					 MODEM_KEY_MGMT_CRED_TYPE_PSK,
					 key, sizeof(key));
		printk("%s\n", err ? "mismatch" : "match");
		if (!err) {
			return 0;
		}
	} else {
        printk("PSK is nonexistent\n");
    }

    printk("Provisioning PSK\n");
	err = modem_key_mgmt_write(SEC_TAG,
				   MODEM_KEY_MGMT_CRED_TYPE_PSK,
				   key, sizeof(key));
	if (err) {
		printk("Failed to provision certificate, err %d\n", err);
		return err;
	}

	return 0;
}

My trace log as follow:

trace-2022-07-14T10-04-46.760Z.zip