What Is Certificate Pinning? A Detailed Guide

If you are a medium or small business owner, keeping your mobile applications safe for you and your customers is important. However, most business owners think using SSL and HTTPS is enough to give them security. It is not true.

Both SSL and HTTPS can’t provide you full security from hackers. Right now, certificate pinning is a method that helps you the most to make your website traffic secure.

In this guide, we will explore everything from what certificate pinning is to how it saves your application from man-in-the-middle attacks.

So, let’s get started!

What Is Certificate Pinning?

Certificate pinning is a security technique that prevents Man-in-the-Middle (MitM) attacks. When one of your clients connects to a web server, it will look for a digital certificate presented by the server to ensure that it has been issued by a trusted Certificate Authority.

But his checking and verifying process is vulnerable to MitM attacks. The hacker presents a fake digital certificate by intercepting the traffic in this attack.

Also Read: What is SSL Pinning & How Does It Work?

Certificate pinning helps to fight against this vulnerability by allowing the clients to specify one or more digital certificates that would be used by the web server. So, when any client connects to the server, the expected certificates are verified. If the certificates don’t match, then it will end the server connection or raise an alert.

In certificate planning, we add a domain name with one or more digital certificates. So, whenever the app establishes a connection with the server, a handshake takes place and both parties exchange messages between them. With this connection, they also establish the encryption algorithms and set the session encryption keys.

During this handshake, the device only receives the server certificate chain after confirming one or more certificates in the chain are trusted ones. The certificate pinning process makes sure that the connection between the app and the official backend is established.

The main purpose of this pinning is to prevent Man-in-the-Middle attack. It also prevents the encrypted data between the app and the backend from getting manipulated by a 3rd party.

How Does Certificate Pinning Work?

Now that we have understood what is certificate pinning, let us understand how pinning works.

Standard Certificate Validation

In a regular certificate-pinning handshake, the client connects to a server and the server presents the client with a digital certificate. Then, the client checks the authenticity of that certificate by verifying that the certificate is signed by a trusted Certificate Authority.

They also check for if the certificate has been expired or manipulated. If all these checking gives the client a clear signal, then they proceed with the connection.

Pinning Trust

With certificate pinning the client can take the trust verification a step further. With this process, they don’t have to only rely on the Certificate Authority system. Because their application or device will have a pre-configured list of digital certificates can can be trusted.

What Is A Man-In-The-Middle Attack?

We are learning so much about certificate pinning, but it’s also important to know what is the Man-In-The-Middle attack and how it works.

When the client uses the mobile application of a business, they make a call according to what they think the server of the business is. But this process is vulnerable to hackers as they can intercept this call and then relay it to the server.

This process gives the man in the middle permission to get the server’s public key and the hacker passes their public key to your client. The attacker can now talk to both the server and the client, but the server and the client are not able to talk to each other.

The hacker gets access to any data passed between your server and the client. They can also modify the data being sent according to them.

How to Implement Certificate Pinning?

Now, we will discuss how you can implement certificate planning in your mobile application.

Understand SSL and Certificates

Before you try to implement certificate pinning, it’s essential to understand what is SSL certificates and how they work. When a mobile application communicates with a server through HTTPS, then the server provides the application with a digital certificate to prove its authenticity. This certificate is signed by a certificate authority.

With certificate pinning, you don’t have to put your entire trust in the certificate authority, instead, you can specify which certificates your app is going to trust with certificate pinning.

Select Certificates

The next step is choosing the digital certificates your app is going to trust. If you prefer, you can keep or extract the public keys from the certificate. These certificates are the ‘pins’ in the pinning process.

Integrate a Library or Implement It Manually

Implement certificate pinning in the app by using a dedicated library or you can manually code it. There are many libraries available online that give you pre-built functionality for certificate pinning.

If you want to do the process manually, then intercept the SSL connection and verify the server’s certificate if it matches the pinned certificates. In a manual implementation, you will have to code the logic for certificate validation.

Implement Pinning Logic

If you code the pinning logic manually, you need to intercept the SSL communication between the app and the server. Then, you have to extract the server’s certificate from the handshake and compare the extracted certificate with the pinned certificate on the app.

If it matches, then the connection can be built. If it doesn’t match, terminate the connection or take necessary security measures.

Handling Errors

While coding the pinning logic, implement some error-handling mechanisms in it as well. If some digital certificate doesn’t match the pinned certificate, it should be able to take proper action against it.

Periodic Updates

Remember that the certificates you are pinning will expire with time, and they will need to be replaced. Make sure the app can replace those expired certificates when necessary.

Testing and QA

Testing and QA in different scenarios are important in certificate pinning. Test the implementation in scenarios such as invalid certificates, certificate expiration, and server changes. Try penetration testing as well to deal with potential vulnerabilities as well.

Documentation

Document the process of certificate pinning and include the certificates you have pinned. Document the other security measures you have taken as well.

Update the App

Regularly updating the app is important with new pinned certificates and security measures to fight potential threats.

What are the Disadvantages of Certificate Pinning?

Till now, we have learned about the various advantages of certificate pinning, let’s see some of the main disadvantages of this process.

Maintenance Complexity

For Certificate pinning, the clients who use your app need to maintain a list of trusted digital certificates. The list of these certificates also needs to be continuously updated according to the certificates present in the server.

All the certificates have their expiration dates and are regularly renewed, so, the client needs to keep the pinned certificate updated. This regularly updating process can be difficult and is prone to human errors which may disrupt services.

Reduced Flexibility

The servers available right now are dynamic and cloud-based, so, in this environment, server certificates change frequently. Here, certificate pinning can cause operational challenges.

Certificates, once they are pinned are inflexible and can hinder smooth transactions between the app and the server.

Risk of Breaking Connections

Sometimes certificate pinning causes the loss of connection and the pinned certificate expires or becomes compromised. In that case, the service is interrupted until the client’s app is updated with the new pinned certificates, they can’t avail of any service.

Lack of Scalability

Certificate pinning is difficult to implement in large-scale applications that need to communicate with a lot of servers, as all those servers will have their digital certificates. Managing all those various certificates might not be very beneficial for the client if they undertake certificate pinning.

What are the Alternatives to Certificate Pinning?

Now, we will explore some of the alternatives that you can apply to ensure security measures other than certificate pinning.

Certificate Transparency

Certificate Transparency is a public log of all issued digital certificates. CT provides transparency and accountability in the certificate issuance process. If one client monitors the CT logs, then they will easily understand the unauthorized certificates.

Also Read: How to Fix ERR_CERTIFICATE_TRANSPARENCY_REQUIRED in Chrome?

The CT process doesn’t solely rely on certificate pinning but adds another layer to verify the certificate. This way the clients can identify the fraud certificates without going through the pinning process.

Online Certificate Status Protocol Stapling

This method allows servers to provide the client with a digitally signed assertion about the status of their certificates. This stapling makes it easy for the client to verify the server’s certificate without depending on Certificate Transparency.

OCSP is a more dynamic approach where the client doesn’t require pinning. This process also reduces the risks associated with outdated certificates.

Conclusion

Certificate pinning enhances the security of any client-server connection and reduces the risk of man-in-the-middle attacks. But this process has its drawbacks as well. The process of maintaining and updating pinned certificates is complex.

In any dynamic environment, the pinning provides less flexibility and there’s a lack of scalability in certificate pinning. These drawbacks make it a less practical choice for many apps. So, there are other options available such as Certificate Transparency (CT) and Online Certificate Status Protocol Stapling (OCSP).

These processes offer good security measures without the limitations of certificate pinning. So, it is advisable to choose between any security measures based on your use case. Just make sure no matter whatever measures you are choosing, the communication between the client and the server is safe and efficient.

FAQs

What is a Certificate Pinning?

Certificate pinning is a process that authenticates the client-server connection by comparing different server certificates. This pinning helps in preventing man-in-the-middle attacks. The process starts with pinning one or several digital certificates to an application. After the pining, when the app connects to any server, it will check if the server’s certificate matches with the pinned certificates or not.

If the certificate doesn’t match, then the connection will not be established. This process makes sure that the connection is built only with trusted servers. It prevents the attackers from hacking or manipulating the data.

What is the Purpose of Certificate Pinning?

One of the main purposes of certificate pinning is to enhance the security measures of online communications. Pinning makes sure that the mobile application only establishes a connection with trusted servers that have authentic digital certificates.

When a specific certificate is pinned to the application, it checks if the certificate matches the one that has been pinned. If the certificates don’t match, then the connection is blocked. This helps in preventing attackers from using fake certificates and manipulating the data. Certificate pinning keeps the client’s personal information safe.  

Is Certificate Pinning a Good Way to Fight against Hackers?

Certificate pinning can be a good way to fight against hackers. It makes sure that your app is only connecting to servers that are trustable. So, even if the hackers try to fake a digital certificate, the app will not accept it. With the pinned certificates, there’s less chance of man-in-the-middle attacks.

But it’s important to regularly update the certificates as all the certificates have expiration dates. Overall, the certificate pinning gives you extra protection to keep your personal information safe from hackers.

What are the Risks of Certificate Pinning?

Certificate pinning comes with certain risks such as if the server updates its certificate, then the app might fail to provide services. The loss in service can frustrate the clients and lead to loss of data as well. Also, if one certificate is compromised, then the app remains vulnerable to it until it is updated.

If the certificates are not pinned properly, then it can make the app less flexible, and in a dynamic environment, it is difficult to handle that as certificates change more frequently. If the user uninstalls the device, then it won’t be able to connect with the server so easily because of the strict certificate pinning rules.

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