RTCCertificates are self-signed certificates used in the DTLS handshake for when setting up a connection with an RTCPeerConnection. This feature allows RTCCertificates to be persisted to storage by an application by implementing the structured clone algorithm. This means RTCCertificates can be saved and loaded from an IndexedDB database, saving the cost of generating new certificates for new sessions.
Docs: https://developers.google.com/web/updates/2016/06/webrtc-ecdsa