To get started, install the net library.

With Maven:


Or using Gradle:


If you haven’t already, you will also need to add Bouncy Castle to your dependencies, and add the Bouncy Castle Security Provider to Java.

Security.addProvider(new BouncyCastleProvider());


Since we’re engaging in peer-to-peer applications, we will define different scenarios for trust.

First off, we will engage in two-way certificate authentication. The server will provide its certificate to the client and the client will also need to provide its identity.

All those settings are taken after the Constellation private enclave network options.


By default, Java uses Certificate Authorities on the machine to authenticate a trusted certificate.


We can also choose to record the fingerprints of incoming connections while authorizing all of them.

Trust On First Use (TOFU)

In this setting, incoming connections are recorded, and their certificates are collected, but only the first certificate assigned to a connection is allowed.

This is a good way to mitigate MITM attacks.


Only explicit hosts and certificate combinations are allowed.


TrustManagerFactory implementations provide trust with JDK and most Java-based servers.

The TrustManagerFactories API creates TrustManagerFactory objects for client and server communications.

As an example, the following method creates a TrustManagerFactory that records incoming connections into a knownServersFile, but only the ones that don’t have a signed CA certificate.

TrustManagerFactories.recordServerFingerprints(knownServersFile, false);


The VertxTrustOptions API is a quick drop-in API to configure Vert.x servers and clients for communications.

In the example below, we set a server to require client authentication and trust clients on first access (TOFU).

HttpServerOptions options = new HttpServerOptions();
httpServer = vertx.createHttpServer(options);

In this example, we set a HTTP client to communicate with servers that are whitelisted only (and not even trust CA-signed certificates):

HttpClientOptions options = new HttpClientOptions();
       .setTrustOptions(VertxTrustOptions.whitelistServers(knownServersFile, false))
client = vertx.createHttpClient(options);