Epoch Markers

This document defines Epoch Markers as a means to establish a notion of freshness among actors in a distributed system. Epoch Markers are similar to "time ticks" and are produced and distributed by a dedicated system known as the Epoch Bell. Systems receiving Epoch Markers do not need to track freshness using their own understanding of time (e.g., via a local real-time clock). Instead, the reception of a specific Epoch Marker establishes a new epoch that is shared among all recipients. This document defines Epoch Marker types, including CBOR time tags, RFC 3161 TimeStampToken, and nonce-like structures. It also defines a CWT Claim to embed Epoch Markers in RFC 8392 CBOR Web Tokens, which serve as vehicles for signed protocol messages.