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CoAP over DTLS

ThingsBoard provides the ability to run CoAP server over DTLS. Both one-way and two-way DTLS are supported. DTLS provisioning requires valid ECDSA certificates. ECDSA keys are smaller than RSA keys and thus more preferable for constrained devices. See comparison article for more details. We recommend to use valid SSL certificates generated using trusted CA authorities and avoid spending time on resolving issues with self-signed certificates. See instructions below on how to configure SSL for certificates stored in PEM file format or Java Keystore.

SSL configuration using PEM certificates file

Available since TB Version 3.3.2

Configure the following environment variables via configuration file, docker-compose or kubernetes scripts. We will use thingsboard.conf for example:

export COAP_DTLS_PEM_CERT=server.pem
export COAP_DTLS_PEM_KEY=server_key.pem


  • COAP_DTLS_ENABLED - Enable/disable SSL support;
  • COAP_DTLS_CREDENTIALS_TYPE - Server credentials type. PEM - pem certificate file; KEYSTORE - java keystore;
  • COAP_DTLS_PEM_CERT - Path to the server certificate file. Holds server certificate or certificate chain, may also include server private key;
  • COAP_DTLS_PEM_KEY - Path to the server certificate private key file. Optional by default. Required if the private key is not present in server certificate file;
  • COAP_DTLS_PEM_KEY_PASSWORD - Optional server certificate private key password.

After completing the setup, start or restart the ThingsBoard server.

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Make sure the certificate files are reachable by ThingsBoard process:

  • Linux: use /etc/thingsboard/conf folder. Make sure the files have same permissions as thingsboard.conf; Use relative file path, e.g. server.pem;
  • Docker Compose: mount or use existing volume to /config folder of the container; Use full file path, e.g. /config/server.pem;
  • K8S: mount separate volume to /https-config or similar folder. Use full file path, e.g. /https-config/server.pem;
  • Windows: use C:\Program Files (x86)\thingsboard\conf\ folder. Make sure the files have same permissions as thingsboard.conf; Use relative file path, e.g. server.pem;

Additional configuration properties

You may configure following additional environment variables via configuration file, docker-compose or kubernetes scripts.

  • COAP_DTLS_BIND_ADDRESS - the bind address for the secure CoAP server. Default value indicates all interfaces;
  • COAP_DTLS_BIND_PORT - the bind port for the secure CoAP server. Default value is 5684;
  • TB_COAP_X509_DTLS_SKIP_VALIDITY_CHECK_FOR_CLIENT_CERT - Skip certificate validity check for client certificates. Default value is false.
  • TB_COAP_X509_DTLS_SESSION_INACTIVITY_TIMEOUT - Maximum inactivity time of DTLS session in milliseconds. Default value is 86400000 which corresponds to one day.
  • TB_COAP_X509_DTLS_SESSION_REPORT_TIMEOUT - Frequency of periodic cleanup of inactive sessions. Default value is 1800000 which corresponds to 30 minutes.

Self-signed certificates generation

Use instructions below to generate your own certificate files. Useful for tests, but time consuming and not recommended for production.

PEM certificate file

Note This step requires Linux based OS with openssl installed.

To generate a server self-signed PEM certificate and private key, use the following command:

openssl ecparam -out server_key.pem -name secp256r1 -genkey
openssl req -new -key server_key.pem -x509 -nodes -days 365 -out server.pem 

You can also add -nodes (short for no DES) if you don’t want to protect your private key with a passphrase. Otherwise, it will prompt you for “at least a 4 character” password.

The days parameter (365) you can replace with any number to affect the expiration date. It will then prompt you for things like “Country Name”, but you can just hit Enter and accept the defaults.

Add -subj ‘/CN=localhost’ to suppress questions about the contents of the certificate (replace localhost with your desired domain).

Self-signed certificates are not validated with any third party unless you import them to the browsers previously. If you need more security, you should use a certificate signed by a certificate authority (CA).

Client Examples

See following resources: