## 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 responsіble 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