MQTT with TLS: Fortifying MQTT Communication Security

Introduction

In our previous articles, we explored authentication and access control mechanisms. Now, it's time to shine a light on the crucial role of Transport Layer Security (TLS) in fortifying MQTT communication. This blog post will focus specifically on TLS and its ability to ensure the integrity, confidentiality, and authenticity of MQTT communication.

Concepts Explained

Before we start, let's get some key concepts explained.

• Handshake: The TLS handshake is a process that establishes a secure connection between the client and the server. During the handshake, the client and the server exchange messages to establish the parameters of the secure connection, such as the encryption algorithms to use, the session keys, and the authentication method.
• Cipher Suite: A cipher suite combines encryption, hashing, and key exchange algorithms to secure the connection. TLS supports multiple cipher suites, and the client and server negotiate the cipher suite during the handshake.
• Certificate: A certificate is a digital document used to establish the identity of the server or the client. The certificate contains the public key of the server or the client, and it is signed by a trusted Certificate Authority (CA).
• Session: A session is a period of communication between the client and the server. During a session, the client and the server exchange data over a secure connection. The session can be terminated by either the client or the server.

Overview of TLS

Transport Layer Security (TLS) is a cryptographic protocol that provides secure communication over the Internet. TLS protects sensitive data such as passwords, credit card information, and personal information from unauthorized access or interception. TLS is widely used in web applications, email, instant messaging, and other applications that require secure communication over the Internet.

TLS provides security through encryption, data integrity, and authentication.

• Encryption ensures that the data transmitted between the client and the server is encrypted, so unauthorized users cannot read it.
• Data integrity ensures that the data is not modified during transmission.
• Authentication ensures that the client is communicating with the intended server and not an imposter.

TLS uses a combination of public-key cryptography and symmetric-key cryptography to achieve these security features.

They perform a handshake process in the initial contact between the client and the server. During the handshake, the client and the server exchange messages to establish the parameters of the secure connection, such as the encryption algorithms to use, the session keys, and the authentication method. TLS supports multiple cipher suites, and the client and server negotiate the cipher suite during the handshake. A certificate is a digital document that is used to establish the identity of the server or the client. The certificate contains the public key of the server or the client, and it is signed by a trusted Certificate Authority (CA). Public Key Infrastructure (PKI) establishes trust between the client and the server.

Why is TLS Essential For MQTT Security?

When it comes to MQTT security, TLS plays a crucial role by ensuring MQTT messages' confidentiality, integrity, authentication, and non-repudiation. It safeguards sensitive data from unauthorized access, tampering, and interception and provides a secure and trusted communication channel between MQTT clients and brokers.

TLS ensures confidentiality by encrypting the data transmitted between MQTT clients and the broker. Without TLS, MQTT messages are sent in plain text, meaning anyone with network access can intercept and read the data. By implementing TLS, the content of the messages remains encrypted and inaccessible to unauthorized parties.

TLS also provides data integrity. It prevents tampering or modification of MQTT messages during transmission. Each message is digitally signed using TLS, guaranteeing that it cannot be altered without detection. The integrity check fails if any unauthorized changes occur, indicating that the data has been tampered with.

Additionally, TLS enables authentication, ensuring that MQTT clients and brokers can verify each other's identities. Through SSL/TLS certificates, clients can verify their connection to a legitimate and authorized broker. This process safeguards against malicious entities attempting to impersonate the broker and establishes trust between clients and the MQTT infrastructure.

Moreover, TLS provides non-repudiation. It uses digital signatures to prevent senders from denying their message transmissions. The digital signature confirms the authenticity and origin of the message, making it possible to prove that a specific client sent a particular message.

Lastly, TLS protects MQTT communication from eavesdropping attacks, where an attacker intercepts and listens to the MQTT messages. It also guards against man-in-the-middle attacks, where an attacker tries to intercept and manipulate the messages exchanged between clients and the broker.

TLS Authentication Methods

One-Way Authentication

One-way authentication is the simplest form of authentication used in TLS. In one-way authentication, the server presents its digital certificate to the client. The client verifies the certificate to ensure it is valid and issued by a trusted CA. Once the certificate is confirmed, the client can establish a secure connection with the server. One-way authentication is sufficient when the client does not need to be authenticated or when the client's identity is not critical.

Two-Way Authentication

Two-way authentication, or mutual authentication (mTLS), is a more secure form of authentication used in TLS. In two-way authentication, both the client and the server authenticate each other. The client presents its digital certificate to the server, and the server verifies the certificate to ensure that it is valid and issued by a trusted CA. The server also presents its digital certificate to the client, and the client verifies the certificate to ensure that it is valid and issued by a trusted CA. Once both certificates are verified, the client and the server can establish a secure connection. Two-way authentication is used when the client and the server need to be authenticated or when the client's identity is critical.

PSK Authentication

In Pre-Shared Key (PSK), a shared secret key is used to authenticate the client and the server. The client and the server agree on a private key before establishing the connection. During the handshake, the client and the server use the secret key to authenticate each other. PSK is used when it is difficult or impossible to use public-key cryptography. This method is less secure than others since the same key is used for every connection.

Certificateless Cryptography

In certificateless cryptography, the client and the server generate a shared secret key using a key agreement protocol, such as Diffie-Hellman. The shared secret key establishes a secure connection between the client and the server. Since the shared secret key is not transmitted over the network, it is not vulnerable to interception or eavesdropping. Certificateless cryptography also eliminates the need for a trusted third party to issue and manage digital certificates, which can simplify the implementation and management of TLS. One major limitation is that it requires both the client and the server to have the same key agreement parameters, which can be challenging in some situations. Additionally, certificateless cryptography is not widely supported by TLS implementations, which can limit its applicability in practice.

Choosing the Authentication Method

Choosing the correct authentication method is crucial in ensuring the security of TLS. The choice of authentication method depends on the level of security required, the ease of implementation, and the resources available.

• One-way authentication is suitable when the client's identity is not critical.
• Two-way authentication is necessary when both the client and the server need to be authenticated.
• PSK is useful when public-key cryptography cannot be used but is less secure than public-key cryptography.
• Certificateless cryptography is useful when digital certificates are unavailable or are not trusted.
• Dedicated Secret per Device is especially useful in scenarios where the devices in the network have different levels of security requirements or where the entire network's security depends on each device's security.

The choice of authentication method should be based on a thorough analysis of the requirements and risks involved.

Implementation Recommendations

Implementing TLS requires careful planning and execution to ensure communication security. Some best practices for TLS implementation are:

• Use the latest version of TLS: Use the latest version of TLS, which provides the most secure encryption and hashing algorithms.
• Use strong cipher suites: Use strong cipher suites that provide a high level of encryption and data integrity.
• Use trusted certificates: Use digital certificates issued by trusted CAs to establish the identity of the server or the client.
• Implement certificate revocation: Implement certificate revocation mechanisms to revoke certificates that have been compromised or expired.
• Monitor certificate expiration: Monitor the expiration of digital certificates to ensure that they are renewed in time.
• Secure key management: Implement a secure key management system to manage the secret keys used for authentication.
• Regularly update and patch software: Regularly update and patch the software used for TLS implementation to ensure any vulnerabilities are addressed.

Conclusion

TLS provides a secure way to communicate over the Internet. Using a dedicated secret per device and choosing the correct authentication method can enhance the security of TLS. By following the implementation best practices provided in this blog, you can leverage the full power of TLS to build a more secure IoT platform.

EMQX has built-in support for TLS/SSL, including one-way/two-ways authentication, the X.509 certificate, load balance SSL and many other security certifications. You can enable SSL/TLS for all protocols supported by EMQX and configure the HTTP API provided by EMQX to use TLS. For more guidance, continue exploring what EMQX has to offer:

• Enabling one-way authentication for EMQX Enterprise
• Enabling two-way authentication for EMQX Enterprise
• Enabling two-way authentication for EMQX Cloud with a custom domain and third-party certificate

For more about EMQX, please check our documentation, GitHub, Slack channel, and forum!