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| <!--* freshness: {owner: 'danilchap' reviewed: '2026-06-17'} *--> |
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| ## Overview |
| |
| WebRTC uses DTLS in two ways: |
| |
| - to negotiate keys for SRTP encryption using |
| [DTLS-SRTP](https://www.rfc-editor.org/info/rfc5763) |
| - as a transport for SCTP which is used by the Datachannel API |
| |
| The W3C WebRTC API represents this as the |
| [DtlsTransport](https://w3c.github.io/webrtc-pc/#rtcdtlstransport-interface). |
| |
| The DTLS handshake happens after the ICE transport becomes writable and has |
| found a valid pair. It results in a set of keys being derived for DTLS-SRTP as |
| well as a fingerprint of the remote certificate which is compared to the one |
| given in the SDP `a=fingerprint:` line. |
| |
| This documentation provides an overview of how DTLS is implemented, i.e how the |
| following classes interact. |
| |
| ## webrtc::DtlsTransport |
| |
| The [`webrtc::DtlsTransport`][1] class is a wrapper around the |
| `webrtc::DtlsTransportInternal` and allows registering observers implementing |
| the `webrtc::DtlsTransportObserverInterface`. The |
| [`webrtc::DtlsTransportObserverInterface`][2] will provide updates to the |
| observers, passing around a snapshot of the transports state such as the |
| connection state, the remote certificate(s) and the SRTP ciphers as |
| [`DtlsTransportInformation`][3]. |
| |
| ## webrtc::DtlsTransportInternal |
| |
| The [`webrtc::DtlsTransportInternal`][4] class is an interface. Its |
| implementation is [`webrtc::DtlsTransportInternalImpl`][5]. The |
| `webrtc::DtlsTransportInternalImpl` sends and receives network packets via an |
| ICE transport. It also demultiplexes DTLS packets and SRTP packets according to |
| the scheme described in |
| [RFC 5764](https://tools.ietf.org/html/rfc5764#section-5.1.2). |
| |
| ## webrtc::DtlsSrtpTranport |
| |
| The [`webrtc::DtlsSrtpTransport`][6] class is responsŃ–ble for extracting the |
| SRTP keys after the DTLS handshake as well as protection and unprotection of |
| SRTP packets via its [`webrtc::SrtpSession`][7]. |
| |
| [1]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/pc/dtls_transport.h;l=30;drc=031d798a20cc5d9c867598a38632accb20c6effe |
| [2]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/api/dtls_transport_interface.h;l=96;drc=031d798a20cc5d9c867598a38632accb20c6effe |
| [3]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/api/dtls_transport_interface.h;l=46;drc=031d798a20cc5d9c867598a38632accb20c6effe |
| [4]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/p2p/dtls/dtls_transport_internal.h;l=49;drc=031d798a20cc5d9c867598a38632accb20c6effe |
| [5]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/p2p/dtls/dtls_transport.h;l=137;drc=031d798a20cc5d9c867598a38632accb20c6effe |
| [6]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/pc/dtls_srtp_transport.h;l=33;drc=031d798a20cc5d9c867598a38632accb20c6effe |
| [7]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/pc/srtp_session.h;l=39;drc=031d798a20cc5d9c867598a38632accb20c6effe |
