DTLS-SRTP: Secure VoIP Encryption Explained

When you make a VoIP call, your voice travels over the internet—and without protection, it can be intercepted. That’s where DTLS-SRTP, a security protocol that encrypts voice data in real time using Datagram Transport Layer Security and Secure Real-time Transport Protocol. It’s the standard for keeping calls private in Zoom, RingCentral, FreePBX, and other modern systems. Unlike basic RTP, which sends audio in plain text, DTLS-SRTP wraps every packet in encryption before it leaves your device. This isn’t just for spies or banks—it’s for any business that cares who hears their sales calls, patient consultations, or team huddles.

DTLS-SRTP doesn’t work alone. It pairs with SIP, the signaling protocol that sets up VoIP calls to negotiate encryption keys before the call starts. Once the handshake is done, SRTP, the actual audio encryption layer takes over, scrambling the voice stream so only the intended device can decode it. This is why call recording tools sometimes miss inbound audio—if the system doesn’t capture the decrypted stream, you get silence. And unlike older methods like SRTP without DTLS, this version prevents man-in-the-middle attacks by verifying the identity of both ends using certificates.

It’s not magic. DTLS-SRTP adds less than 3% CPU load, according to real-world tests, and doesn’t hurt call quality—even with high-bitrate codecs like G.722 or Opus. But it only works if your phones, servers, and firewalls all support it. Many small businesses skip it because their cheap IP phones don’t enable it by default. Others turn it off thinking it slows things down, not realizing that unencrypted calls are far riskier than a tiny delay. If you’re using FreePBX, RingCentral, or any system that lets you configure security settings, check if DTLS-SRTP is active. Turn it on. It’s one of the easiest ways to lock down your voice network.

You’ll find posts below that dig into how SRTP affects codec performance, how to fix recording issues caused by audio routing, and how to harden your VoIP system against eavesdropping. These aren’t theoretical guides—they’re fixes for problems real teams face every day. Whether you’re setting up a new phone system, troubleshooting call quality, or just trying to keep your conversations private, understanding DTLS-SRTP is the first step.