SIP • Last Updated 9/29/2023

SIP Trunk Encryption - Guide to Secure SIP Trunking

Learn how SIP Trunk encryption is helping secure SIP connections, and helping to eliminate security concerns surrounding VoIP.

By Brian Segal

Encrypted SIP Trunk calls

SIP trunking is a modern and increasingly common method for connecting phone calls over the internet. SIP trunking offers many advantages over traditional telephone networks, but the virtual nature of SIP connections and the integration of internet connections raises questions about security.

SIP trunk encryption is a huge part of the answer to these security concerns, and understanding how SIP trunk encryption works will help you choose the best SIP trunking provider and feel more secure making calls through a SIP trunk connection.

Is SIP Trunking Secure?

The short answer is, yes. SIP trunking is secure. The long (and more nuanced) answer is that SIP trunking can be plenty secure, so long as things are done right. Strong SIP trunk encryption does most of the work in securing your SIP connections.

However, good SIP trunk security is a two-sided process. On one side, your SIP trunking provider needs to do their part to keep your call data secure for as long as it’s on their network. The other side of this equation is what you do to protect your end of your SIP trunk connection.

We’ll get into the technical details of SIP trunk encryption later on in this article. But, for now, just understand that your SIP trunking provider should handle most of the technical aspects of securing your SIP trunk. You’ll have to be vigilant about protecting your own phones, other VoIP devices, and passwords.

To sum up, SIP trunking is very secure, so long as it’s protected by this combination of technical security (SIP trunk encryption and private networks) and good security practices on your end. This two-stage approach to SIP trunk security helps mitigate the potential vulnerabilities of SIP trunking.

Where SIP Trunks are Vulnerable

The common theme of SIP trunk vulnerability is the human factor. While some vulnerabilities are related entirely to the technology used to connect calls through SIP trunk, most vulnerabilities start with people. These are some of the potential attacks and how they get past your defenses:

  • Phone number spoofing: With the right information, a scammer can make it look like they’re calling from your phone number. Scammers usually use phone number spoofing to hide their true phone number when they make scam calls or to charge calls to your account.

  • Call interception. This is also commonly called a “man-in-the-middle” attack. And it’s one of the few attacks that do not always require social engineering or some sort of human error. A man-in-the-middle attack is where a hacker gains access to part of the path that your call takes, such as a router or server that transports call data. From that point, the bad actor can extract or interrupt call data as it passes through the breached piece of equipment.

  • DDoS attacks: A DDoS (Distributed Denial of Service) attack is where a cybercriminal uses many computers to overwhelm your network with data. This causes your network to stop functioning. A DDoS attack requires some sort of access to your network, otherwise it’s impossible to inject the data to overwhelm the network.

  • Malware: Malware is just malicious software (hence the name, “malware). Most malware is designed to steal personal or financial information. Most malware attacks require some sort of social engineering. Usually, an employee is tricked into installing the malware or handing over a username and password through some sort of email or phone scam, called a “phishing attack.”

  • Software and firmware vulnerabilities: Almost all of the equipment that connects to your SIP trunk runs some sort of software or firmware. Bad actors can exploit weaknesses in that software and firmware to gain access to your network and intercept calls, perform DDoS attacks, or potentially install malware.

These vulnerabilities can present problems if someone manages to exploit them. But working with a good SIP trunking provider and a bit of vigilance on your part can mitigate all of them.

Best Practices for Safe SIP Trunking

As we mentioned earlier, most SIP trunk vulnerabilities require some sort of social engineering or exploitation of people to work. So most of the best practices for safe SIP trunking will involve implementing some general cybersecurity best practices.

Here’s what you can do:

  • Use private networks whenever you can: Using private networks reduces the chances of suffering a man-in-the-middle or DDoS attack, because private networks have less public exposure. However, it can be tricky to use private networks when your calls connect through your telecom carrier’s networks. If you can, work with a telecom carrier that owns and operates their own network. This will give you the best protection from attacks that require access to the networks that connect your calls.

  • Train team members to spot and avoid social engineering scams: Almost any attack can be executed if the criminal has a username and password. But malware infections are especially reliant on social engineering because they almost always have to trick people into installing the malware or giving up their login information. Training your employees on how to avoid being a victim of these attacks goes a long way in preventing malware infections and other attacks.

  • Keep your software and firmware up to date: Most firmware and software providers work hard to eliminate weaknesses in their products. So keeping your software and firmware up to date will usually protect you from these vulnerabilities.

  • Choose a SIP trunking provider that encrypts data from end to end: If your call data becomes unencrypted in transport, it’s vulnerable to being intercepted by a man-in-the-middle attack. SIP trunk encryption protects against this sort of attack, but only when it keeps your call data encrypted for as long as it’s in transit. Since you must depend on your SIP trunking providers network for connecting your calls, it’s important to choose your SIP provider carefully. Evaluating SIP trunk providers requires a slightly deeper understanding of SIP trunk encryption.

What is SIP Trunk Encryption?

SIP trunk encryption can get a bit technical. But you don’t have to be a cybersecurity or networking expert to understand how it works well enough to make the best choices when it comes to your call and data security.

Here’s a simplified, but technical description of how SIP trunk encryption works:

Generally speaking, there are two layers that need to be encrypted in your SIP connection: the data layer and the audio layer. The data layer is a series of data packets that contain information about the SIP connection—the IP address for the PBX system and connected phone and potentially user profiles associated with that phone. The audio layer is a series of audio packets that contain the actual sounds of the phone conversation.

Both of these layers need to be encrypted.

If the data layer is not encrypted, a cybercriminal could intercept the call signal and extract information about the connected phone, PBX system, and connected networks. If the audio layer is not encrypted, it’s possible for bad actors to intercept the call signal and listen to the conversation.

There are protocols for encrypting both layers, such as TLS (Transport Layer Security) protocol, SRTP (Secure Real-Time Transport Protocol), and others.

One of the most common configurations uses TLS encryption to protect the data layer and SRTP encryption to protect the audio data. If you work with a quality SIP trunking provider, they should have SIP trunk encryption that encrypts both layers for maximum security.

While encryption is a massive piece of the puzzle in securing SIP connections, reducing the potential for bad actors to intercept call data is also important. If a cybercriminal cannot access the call data, there’s no way for them to extract information from that data.

The best way to do this is to keep calls on private networks as much as possible. The public internet is incredible for a lot of things. But it’s not great for call security. A security focused SIP trunking provider will invest a lot of resources in building and maintaining private networks, and keeping calls on those networks whenever it’s possible.

So, as you consider SIP trunking providers, look at their encryption and the networks they use to connect your calls.

Discover Telnyx’s Unmatched SIP Security

Want to make it super easy to get the SIP trunk encryption you need?

Telnyx delivers SIP trunk connections over a private network that protects your call data from end to end with TLS, SRTP, and ZRTP encryption for no additional cost, and protects your numbers from spoofing and toll fraud. Reach out to a Telnyx encryption and SIP security expert to get all your questions answered.

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