| Philipp Hancke | ada0012 | 2021-05-11 06:51:29 | [diff] [blame] | 1 | <?% config.freshness.reviewed = '2021-05-07' %?> |
| 2 | <?% config.freshness.owner = 'hta' %?> |
| 3 | |
| 4 | ## Overview |
| 5 | |
| 6 | WebRTC uses DTLS in two ways: |
| Philipp Hancke | ada0012 | 2021-05-11 06:51:29 | [diff] [blame] | 7 | |
| Artem Titov | 940108b | 2021-05-26 10:47:34 | [diff] [blame] | 8 | * to negotiate keys for SRTP encryption using |
| 9 | [DTLS-SRTP](https://www.rfc-editor.org/info/rfc5763) |
| 10 | * as a transport for SCTP which is used by the Datachannel API |
| Philipp Hancke | ada0012 | 2021-05-11 06:51:29 | [diff] [blame] | 11 | |
| Artem Titov | 940108b | 2021-05-26 10:47:34 | [diff] [blame] | 12 | The W3C WebRTC API represents this as the |
| 13 | [DtlsTransport](https://w3c.github.io/webrtc-pc/#rtcdtlstransport-interface). |
| 14 | |
| 15 | The DTLS handshake happens after the ICE transport becomes writable and has |
| 16 | found a valid pair. It results in a set of keys being derived for DTLS-SRTP as |
| 17 | well as a fingerprint of the remote certificate which is compared to the one |
| 18 | given in the SDP `a=fingerprint:` line. |
| Philipp Hancke | ada0012 | 2021-05-11 06:51:29 | [diff] [blame] | 19 | |
| 20 | This documentation provides an overview of how DTLS is implemented, i.e how the |
| 21 | following classes interact. |
| 22 | |
| 23 | ## webrtc::DtlsTransport |
| Philipp Hancke | ada0012 | 2021-05-11 06:51:29 | [diff] [blame] | 24 | |
| Artem Titov | 940108b | 2021-05-26 10:47:34 | [diff] [blame] | 25 | The [`webrtc::DtlsTransport`][1] class is a wrapper around the |
| 26 | `cricket::DtlsTransportInternal` and allows registering observers implementing |
| 27 | the `webrtc::DtlsTransportObserverInterface`. The |
| 28 | [`webrtc::DtlsTransportObserverInterface`][2] will provide updates to the |
| 29 | observers, passing around a snapshot of the transports state such as the |
| 30 | connection state, the remote certificate(s) and the SRTP ciphers as |
| 31 | [`DtlsTransportInformation`][3]. |
| 32 | |
| 33 | ## cricket::DtlsTransportInternal |
| 34 | |
| 35 | The [`cricket::DtlsTransportInternal`][4] class is an interface. Its |
| 36 | implementation is [`cricket::DtlsTransport`][5]. The `cricket::DtlsTransport` |
| 37 | sends and receives network packets via an ICE transport. It also demultiplexes |
| 38 | DTLS packets and SRTP packets according to the scheme described in |
| 39 | [RFC 5764](https://tools.ietf.org/html/rfc5764#section-5.1.2). |
| Philipp Hancke | ada0012 | 2021-05-11 06:51:29 | [diff] [blame] | 40 | |
| 41 | ## webrtc::DtlsSrtpTranport |
| Artem Titov | 940108b | 2021-05-26 10:47:34 | [diff] [blame] | 42 | |
| 43 | The [`webrtc::DtlsSrtpTransport`][6] class is responsŃ–ble for extracting the |
| 44 | SRTP keys after the DTLS handshake as well as protection and unprotection of |
| 45 | SRTP packets via its [`cricket::SrtpSession`][7]. |
| Philipp Hancke | 4a54be7 | 2021-05-17 08:20:14 | [diff] [blame] | 46 | |
| Tony Herre | b0ed120 | 2021-07-22 15:40:44 | [diff] [blame] | 47 | [1]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/pc/dtls_transport.h;l=32;drc=6a55e7307b78edb50f94a1ff1ef8393d58218369 |
| 48 | [2]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/api/dtls_transport_interface.h;l=76;drc=34437d5660a80393d631657329ef74c6538be25a |
| 49 | [3]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/api/dtls_transport_interface.h;l=41;drc=34437d5660a80393d631657329ef74c6538be25a |
| 50 | [4]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/p2p/base/dtls_transport_internal.h;l=63;drc=34437d5660a80393d631657329ef74c6538be25a |
| 51 | [5]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/p2p/base/dtls_transport.h;l=94;drc=653bab6790ac92c513b7cf4cd3ad59039c589a95 |
| 52 | [6]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/pc/dtls_srtp_transport.h;l=31;drc=c32f00ea9ddf3267257fe6b45d4d79c6f6bcb829 |
| Philipp Hancke | 4a54be7 | 2021-05-17 08:20:14 | [diff] [blame] | 53 | [7]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/pc/srtp_session.h;l=33;drc=be66d95ab7f9428028806bbf66cb83800bda9241 |
