Eclipse Californium is a Java implementation of RFC7252 - Constrained Application Protocol for IoT Cloud services. Thus, the focus is on scalability and usability instead of resource-efficiency like for embedded devices. Yet Californium is also suitable for embedded JVMs.

More information can be found at http://eclipse.dev/californium/ and http://coap.technology/.

Like to help improving Californium? Then consider to contribute.

You need to have a working maven installation to build Californium. Then simply run the following from the project's root directory:

$ mvn clean install

Executable JARs of the examples with all dependencies can be found in the demo-apps/run folder.

The build-process in branch main is tested for jdk 7, jdk 8, jdk 11 and jdk 17. For jdk 7 the revapi maven-plugin is disabled, it requires at least java 8.

Note: the build **has been" tested long ago. In the meantime too much has changed. Please focus on using jdk 17 to build it.

To generate the javadocs, add "-DcreateJavadoc=true" to the command line and set the JAVA_HOME.

$ mvn clean install -DcreateJavadoc=true

In the meantime, JDK 7 is pretty deprecated! The next major version (4) will not longer support it! It hopefully comes this year (2024).

Californium 2.x and newer can be used with java 7 or newer. In order to use plugins, which are only supported for newer jdks, the --release option is used (requires java 9 or newer to build it).

If you want to build it with a jdk 7, the toolchain plugin could be used, but requires manually remove the maven.compiler.release property in the pom.xml. That requires also a toolchains configuration in "toolchains.xml" in your maven ".m2" folder

<?xml version="1.0" encoding="UTF8"?>
<toolchains>
	<!-- JDK toolchains -->
	<toolchain>
		<type>jdk</type>
		<provides>
			<version>1.7</version>
		</provides>
		<configuration>
			<jdkHome>path..to..jdk7...home</jdkHome>
		</configuration>
	</toolchain>
</toolchains>

To use the jdk7 toolchain, add "-DuseToolchain=true" to the command line.

$ mvn clean install -DuseToolchain=true

To use the jdk7 toolchain and create javadocs, add "-DuseToolchainJavadoc=true" to the command line (JAVA_HOME is not required).

$ mvn clean install -DuseToolchainJavadoc=true

To support EdDSA, either java 17 or java 11 with ed25519-java is required at runtime. Using java 17 (or newer) to build Californium, leaves out ed25519-java, using java 11 for building, includes ed25519-java by default. If ed25519-java should NOT be included into the californium's jars, add -Dno.net.i2p.crypto.eddsa=true to maven's arguments.

$ mvn clean install -Dno.net.i2p.crypto.eddsa=true

Note: if "-DuseToolchain=true" is used and the actual jdk to build is java 11, you must disable the i2p eddsa support as well.

# java 11 with java 7 toolchain
$ mvn clean install -DuseToolchain=true -Dno.net.i2p.crypto.eddsa=true

In that case, it's still possible to use ed25519-java, if the eddsa-0.3.0.jar is provided to the classpath separately.

Note: using the oracle build 28 of openjdk 11 uncovers, that calling EdDSAEngine.engineSetParameter(null) fails with ǸullPointerException instead of InvalidAlgorithmParameterException. That causes to fail the verification of the signature at all. Using the aptopen build seems not to call EdDSAEngine.engineSetParameter(null) and therefore works.

ed25519-java seems to be not longer maintained. It's therefore recommended to update to newer jdks (e.g. 17) or to use Bouncy Castle (see next section, even if the Bouncy Castle support is experimental).

With 3.0 a first, experimental support for using Bouncy Castle (version 1.69, bcprov-jdk15on, bcpkix-jdk15on, and, for tls, bctls-jdk15on) is implemented. With 3.3 the tests are using the updated version 1.70 (for tls also bcutil-jdk15on is used additionally), with 3.8 version 1.72, with 3.9 version 1.74, and with 3.10 to version 1.77.

To demonstrate the basic functions, run the unit-tests using the profile bc-tests

$ mvn clean install -Pbc-tests

Supporting Bouncy Castle for the unit test uncovers a couple of differences, which required to adapt the implementation. It is assumed, that more will be found and more adaption will be required. If you find some, don't hesitate to report issues, perhaps research and analysis, and fixes. On the other hand, the project Californium will for now not be able to provide support for Bouncy Castle questions with or without relation to Californium. You may create issues, but it may be not possible for us to answer them.

On issue seems to be the SecureRandom generator of BC. Dependent on the runtime environment, that is based on SecureRandom.getInstanceStrong(), which has blocking behaviour by default. If the platform your application runs on, has not enough entropy to start the SecureRandom, BC waits until that gets available. In common cases, that starts quite fast, but in some cases, that takes up to 60s (and more).

One option to overcome that on some linux variants is using rng-tools. That may help to provide more entropy.

A second option o overcome that is to setup CALIFORNIUM_JCE_PROVIDER using the value BC_NON_BLOCKING_RANDOM instead of BC. The JceProviderUtil then adapts SecureRandom to use a, maybe weaker, non-blocking SecureRandom. If that works, depends unfortunately on your platform, so especially for Android, that may not work. In that cases, please use BC as CALIFORNIUM_JCE_PROVIDER and configure "securerandom.strongAlgorithms" ahead with

Security.setProperty("securerandom.strongAlgorithms", "<your-android-algorithm>");

according your android variant. That may require some analysis by you.

With that, it gets very time consuming to test all combinations. Therefore, if you need a specific one, please test it on your own. If you consider, that some adaption is required, let us know by creating an issue or PR.

We are publishing Californium's artifacts for milestones and releases to Maven Central. To use the latest released version as a library in your projects, add the following dependency to your pom.xml (without the dots ...):

  <dependencies>
    ...
    <dependency>
            <groupId>org.eclipse.californium</groupId>
            <artifactId>californium-core</artifactId>
            <version>3.11.0</version>
    </dependency>
    ...
  </dependencies>
  ...

You can also be bold and try out the most recent build from main. However, we are not publishing those to Maven Central but to Californium's project repository at Eclipse only. You will therefore need to add the Eclipse Repository to your pom.xml first:

  <repositories>
    ...
    <repository>
      <id>repo.eclipse.org</id>
      <name>Californium Repository</name>
      <url>https://repo.eclipse.org/content/repositories/californium/</url>
    </repository>
    ...
  </repositories>

You can then simply depend on 3.12.0-SNAPSHOT.

The project can be easily imported into a recent version of the Eclipse IDE. Make sure to have the following before importing the Californium (Cf) projects:

• Eclipse EGit (should be the case with every recent Eclipse version)
• m2e - Maven Integration for Eclipse (should be the case with every recent Eclipse version)
• UTF-8 workspace text file encoding (Preferences » General » Workspace)

Then choose [Import... » Maven » Existing Maven Projects] to import californium - parent together with all sub-modules into Eclipse.

The project can also be imported to IntelliJ as follows:

In IntelliJ, choose [File.. » Open] then select the location of the cloned repository in your filesystem. IntelliJ will then automatically import all projects and resolve required Maven dependencies.

A test server is running at coap://californium.eclipseprojects.io:5683/

It is an instance of the cf-plugtest-server from the demo-apps. The root resource responds with its current version.

For a preview to the Return Routability Check for DTLS 1.2 and DTLS 1.3 experimental support, please read feature/rrc - branch.

Please note: The server is intended to test the interoperability of CoAP and DTLS 1.2. Data sent to that server is typically "Hello world". The data is public visible to all other users and is removed on any restart. Please don't send data, which requires "data privacy", the sandbox server is not intended for such usage.

More information can be found at http://www.eclipse.org/californium and technical details at https://projects.eclipse.org/projects/iot.californium.

Another interop server with a different implementation can be found at coap://coap.me:5683/. More information can be found at http://coap.me/.

The server uses the x509 Demo Certificates, which are usually recreated and replaced once a year. And the PSK credentials:

Note: TLS supports only the x509 Demo Certificates.

The server has a resource only accessible using OSCORE under "/oscore". It is configured with the following security material (client side):

Master Secret: 0x0102030405060708090a0b0c0d0e0f10 (16 bytes)
Master Salt:   0x9e7ca92223786340 (8 bytes)
Sender ID:     0x01 (1 byte)
Recipient ID:  0x02 (1 byte)
ID Context:    0x37cbf3210017a2d3 (8 bytes)
(See up to date parameters in "/oscoreInfo" resource)

Note that the server supports running the Appendix B.2 context rederivation procedure. This is necessary as requests from new clients would otherwise be considered replays (as the server's replay window is filled up from earlier clients). To access this resource without using the Appendix B.2 procedure, an appropriate Sender Sequence Number to use and the current ID Context can be retrieved from the resource "/oscoreInfo" using plain CoAP.

Currently Californium's OSCORE supports following algorithms:

OSCORE Encryption:

• AES_CCM_16_64_128, id 10
• AES_CCM_64_64_128, id 12
• AES_CCM_16_128_128, id 30
• AES_CCM_64_128_128, id 32

OSCORE Key Rederivation:

• HKDF_HMAC_SHA_256, id -10
• HKDF_HMAC_SHA_512, id -11

For some systems (particularly when multicasting), it may be necessary to specify/restrict californium to a particular network interface, or interfaces. This can be achieved by setting the COAP_NETWORK_INTERFACES JVM parameter to a suitable regex, for example:

java -DCOAP_NETWORK_INTERFACES='.*wpan0' -jar target/cf-helloworld-server-3.10.0.jar MulticastTestServer

A bug, an idea, an issue? Join the Mailing list or create an issue here on GitHub.

Please check out our contribution guidelines

There are a couple of enhancement issues, which have been closed for longer inactivity. Maybe, if you like to help and spend some time, you will be welcome.