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Setting up two-way TLS

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This tutorial will walk you through the process of protecting your application with mutual TLS, which enables secured connection (HTTPS) and enables you to choose who is allowed to access your application.

This sample project demonstrates a basic setup of a server and a client. The communication between the server and client happens through HTTP, so there is no encryption at all. The goal is to ensure that all communication happens in a secure way.

These are the following steps:

  1. Starting the server
  2. Saying hello to the server (without encryption)
  3. Enabling HTTPS on the server (one-way TLS)
  4. Require the client to identify itself (two way TLS)
  5. Two way TLS based on trusting the Certificate Authority

Starting the server

Required to have:

  1. At least Java 8, Recommended: Java 11
  2. Maven 3.5.0
  3. Eclipse, Intellij IDEA (or any other text editor like VIM)
  4. A terminal
  5. Openssl (Windows users can get it from here: https://git-scm.com/)
  6. Clone the project from: https://github.com/Hakky54/mutual-tls

Start the server by running the main method of the app class in the server project.

Saying hello to the server (without encryption)

Currently, the server is running on the default port of 8080 without encryption. You can call the hello endpoint with the following curl command in the terminal:

curl -i -XGET http://localhost:8080/api/hello

It should give you the following response:

HTTP/1.1 200
Content-Type: text/plain;charset=UTF-8
Content-Length: 5
Date: Sun, 11 Nov 2018 14:21:50 GMT

Hello

You can also call the server with the provided client in the client directory. The client is an integration test based on Cucumber, and you can start it by running the ClientRunnerIT class. There is a Hello.feature file that describes the steps for the integration test. You can find it in the test resources of the client project.

There is another way to run the server and client and that is with the following command: mvn clean install

Enabling HTTPS on the server (one-way TLS)

Now, you will learn how to secure your server by enabling TLS. You can do that by adding the required properties to the application properties file named: application.yml

Add the following property:

server:
  port: 8443
  ssl:
    enabled: true

You will probably ask yourself why the port is set to 8443. The port convention for a tomcat server with https is 8443, and for http, it is 8080. So, we could use port 8080 for https connections, but it is a bad practice. See Wikipedia for more information about port conventions.

Restart the server so that it can apply the changes you made. You will probably get the following exception: IllegalArgumentException: Resource location must not be null.

You are getting this message because the server requires a keystore with the certificate of the server to ensure that there is a secure connection with the outside world. The server can provide you more information if you provide the following VM argument: -Djavax.net.debug=SSL,keymanager,trustmanager,ssl:handshake

To solve this issue, you are going to create a keystore with a public and private key for the server. The public key will be shared with users so that they can encrypt the communication. The communication between the user and server can be decrypted with the private key of the server. Please never share the private key of the server, because others could intercept the communication and will be able to see the content of the encrypted communication.

To create a keystore with a public and private key, execute the following command in your terminal:

keytool -genkeypair -keyalg RSA -keysize 2048 -alias hakan -dname "CN=Hakan,OU=Altindag,O=Luminis,C=NL" -ext "SAN:c=DNS:localhost,IP:127.0.0.1" -validity 3650 -keystore server/src/main/resources/identity.jks -storepass secret -keypass secret -deststoretype pkcs12

Now, you need to tell your server where the location of the keystore is and provide the passwords. Paste the following in your application.yml file:

server:
  port: 8443
  ssl:
    enabled: true
    key-store: classpath:identity.jks
    key-password: secret
    key-store-password: secret

Congratulations! You enabled a TLS-encrypted connection between the server and the client! Now, you can try to call the server with the following curl command: curl -i --insecure -v -XGET https://localhost:8443/api/hello

Let’s also run the client in the ClientRunnerIT class.

You will see the following error message: java.net.ConnectException: Connection refused (Connection refused). It looks like the client is trying to say hello to the server but the server is not there. The problem is that the client it trying to say hello to the server on port 8080 while it is active on the port 8443. Apply the following changes to the HelloStepDefs class:

From:

private static final String SERVER_URL = "http://localhost:8080";

To:

private static final String SERVER_URL = "https://localhost:8443";

Require the client to identify itself (two way TLS)

The next step is to require the authentication of the client. This will force the client to identify itself, and in that way, the server can also validate the identity of the client and whether or not it is a trusted one. You can enable this by telling the server that you also want to validate the client with the property client-auth. Put the following properties in the application.yml of the server:

server:
  port: 8443
  ssl:
    enabled: true
    key-store: classpath:identity.jks
    key-password: secret
    key-store-password: secret
    client-auth: need

If you run the client, it will fail with the following error message: javax.net.ssl.SSLHandshakeException: Received fatal alert: bad_certificate. This indicates that the certificate of the client is not valid because there is no certificate at all. So, let’s create one with the following command:

keytool -genkeypair -keyalg RSA -keysize 2048 -alias suleyman -dname "CN=Suleyman,OU=Altindag,O=Altindag,C=NL" -ext "SAN:c=DNS:localhost,IP:127.0.0.1" -validity 3650 -keystore client/src/test/resources/identity.jks -storepass secret -keypass secret -deststoretype pkcs12

You also need to create a truststore. A truststore is a suitcase containing trusted certificates. The client or server will compare the certificate, which it will receive during the SSL Handshake process with the content of its truststore. If there is a match, then the SSL Handshake process will continue. Before creating the truststores, you need to have the certificates of the client and server. You can get it with the following command:

Export certificate of the client

keytool -exportcert -keystore client/src/test/resources/identity.jks -storepass secret -alias suleyman -rfc -file client/src/test/resources/client.cer

Export certificate of the server

keytool -exportcert -keystore server/src/main/resources/identity.jks -storepass secret -alias hakan -rfc -file server/src/main/resources/server.cer

Now, you can create the truststore for the client and import the certificate of the server with the following command:

keytool -keystore client/src/test/resources/truststore.jks -importcert -file server/src/main/resources/server.cer -alias hakan -storepass secret

The next step is to do the same for the truststore of the server:

keytool -keystore server/src/main/resources/truststore.jks -importcert -file client/src/test/resources/client.cer -alias suleyman -storepass secret

You created the two keystores for the client. Unfortunately, the client is not aware of this. Now, you need to tell that it needs to use the keystores with the correct location and password. You also need to tell the client that ssl is enabled. Provide the following property in the application.yml file of the client:

client:
  ssl:
    enabled: true
    key-store: identity.jks
    key-password: secret
    key-store-password: secret
    trust-store: truststore.jks
    trust-store-password: secret

The server is also not aware of the newly created truststore. Therefore replace the current properties with the following properties:

server:
  port: 8443
  ssl:
    enabled: true
    key-store: classpath:identity.jks
    key-password: secret
    key-store-password: secret
    trust-store: classpath:truststore.jks
    trust-store-password: secret
    client-auth: need

If you run the client again, you will see that the test passed and that the client received the hello message from the server in a secured way. Congratulations! You finished installing two-way TLS!

Two way TLS based on trusting the Certificate Authority

There is another way to have mutual authentication and that is based on trusting the Certificate Authority. It has pros and cons.

Pros

  • Client’s do not need to add the certificate of the server
  • Server does not need to add all the certificates of the clients
  • Maintenance will be less because only the Certificate Authority’s certificate validity can expire

Cons

  • You don’t have control anymore for which applications are allowed to call your application. You give permission to any application who has a signed certificate by the Certificate Authority.

These are the following steps:

  1. Creating a Certificate Authority
  2. Creating a Certificate Signing Request
  3. Signing the certificate with the Certificate Signing Request
  4. Replace unsigned certificate with a signed one
  5. Trusting the Certificate Authority only

Creating a Certificate Authority

Normally there is already a Certificate Authority and you need to provide your certificate to have it signed. Here you will create your own Certificate Authority and sign the Client and Server certificate with it. To create one you can execute the following command:

keytool -genkeypair -keyalg RSA -keysize 2048 -alias root-ca -dname "CN=Root-CA,OU=Certificate Authority,O=Luminis,C=NL" -validity 3650 -keystore root-ca/identity.jks -storepass secret -keypass secret -deststoretype pkcs12

Or you can use the one which is already provided in the repository, see identity.jks in the root-ca directory.

Creating a Certificate Signing Request

To get your certificate signed you need to provide a Certificate Signing Request (.csr) file. This can be created with the following command:

Certificate Signing Request for the server

keytool -certreq -keystore server/src/main/resources/identity.jks -alias hakan -keypass secret -storepass secret -keyalg rsa -file server/src/main/resources/server.csr

Certificate Signing Request for the client

keytool -certreq -keystore client/src/test/resources/identity.jks -alias suleyman -keypass secret -storepass secret -keyalg rsa -file client/src/test/resources/client.csr