b0ed12099f
As part of go/coil update code search links to not point to the "master" branch. Bug: chromium:1226942 Change-Id: I0ae9e84ecc660f789a69fe0b226f93bbc39a8a66 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/226081 Commit-Queue: Tony Herre <toprice@chromium.org> Reviewed-by: Harald Alvestrand <hta@webrtc.org> Cr-Commit-Position: refs/heads/master@{#34531}
54 lines
2.9 KiB
Markdown
54 lines
2.9 KiB
Markdown
<?% config.freshness.reviewed = '2021-05-07' %?>
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<?% config.freshness.owner = 'hta' %?>
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## Overview
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WebRTC uses DTLS in two ways:
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* to negotiate keys for SRTP encryption using
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[DTLS-SRTP](https://www.rfc-editor.org/info/rfc5763)
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* as a transport for SCTP which is used by the Datachannel API
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The W3C WebRTC API represents this as the
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[DtlsTransport](https://w3c.github.io/webrtc-pc/#rtcdtlstransport-interface).
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The DTLS handshake happens after the ICE transport becomes writable and has
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found a valid pair. It results in a set of keys being derived for DTLS-SRTP as
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well as a fingerprint of the remote certificate which is compared to the one
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given in the SDP `a=fingerprint:` line.
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This documentation provides an overview of how DTLS is implemented, i.e how the
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following classes interact.
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## webrtc::DtlsTransport
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The [`webrtc::DtlsTransport`][1] class is a wrapper around the
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`cricket::DtlsTransportInternal` and allows registering observers implementing
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the `webrtc::DtlsTransportObserverInterface`. The
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[`webrtc::DtlsTransportObserverInterface`][2] will provide updates to the
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observers, passing around a snapshot of the transports state such as the
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connection state, the remote certificate(s) and the SRTP ciphers as
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[`DtlsTransportInformation`][3].
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## cricket::DtlsTransportInternal
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The [`cricket::DtlsTransportInternal`][4] class is an interface. Its
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implementation is [`cricket::DtlsTransport`][5]. The `cricket::DtlsTransport`
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sends and receives network packets via an ICE transport. It also demultiplexes
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DTLS packets and SRTP packets according to the scheme described in
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[RFC 5764](https://tools.ietf.org/html/rfc5764#section-5.1.2).
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## webrtc::DtlsSrtpTranport
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The [`webrtc::DtlsSrtpTransport`][6] class is responsіble for extracting the
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SRTP keys after the DTLS handshake as well as protection and unprotection of
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SRTP packets via its [`cricket::SrtpSession`][7].
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[1]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/pc/dtls_transport.h;l=32;drc=6a55e7307b78edb50f94a1ff1ef8393d58218369
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[2]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/api/dtls_transport_interface.h;l=76;drc=34437d5660a80393d631657329ef74c6538be25a
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[3]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/api/dtls_transport_interface.h;l=41;drc=34437d5660a80393d631657329ef74c6538be25a
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[4]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/p2p/base/dtls_transport_internal.h;l=63;drc=34437d5660a80393d631657329ef74c6538be25a
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[5]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/p2p/base/dtls_transport.h;l=94;drc=653bab6790ac92c513b7cf4cd3ad59039c589a95
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[6]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/pc/dtls_srtp_transport.h;l=31;drc=c32f00ea9ddf3267257fe6b45d4d79c6f6bcb829
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[7]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/pc/srtp_session.h;l=33;drc=be66d95ab7f9428028806bbf66cb83800bda9241
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