If a signature is not present but an author is provided by a layer below, the message is to be relayed to third parties and its considered plausibly deniable.
The payload is encoded using [Transit format](https://github.com/cognitect/transit-format). Transit was chosen over JSON in order to reduce the bandwidth.
* 0: `c4` is a decoder handler identification for the current payload format. Identifications allow to register handlers for many different types of payload
* 1: array which items correspond to the described payload fields above
For more details regarding serialization and deserialization please consult [transit format](https://github.com/cognitect/transit-format) specification.
Message types are required to decide how a particular message is encrypted and what metadata needs to be attached when passing a message to the transport layer. For more on this, see [Status Whisper Usage Specification](./status-whisper-usage-spec.md).
<!-- TODO: This reference is a bit odd, considering the layer payloads should interact with is Secure Transport, and not Whisper. This requires more detail -->
`timestamp` MUST be Unix time calculated when the message is created. Because the peers in the Whisper network should have synchronized time, `timestamp` values should be fairly accurate among all Whisper network participants.
`clock` SHOULD be calculated using the algorithm of [Lamport timestamps](https://en.wikipedia.org/wiki/Lamport_timestamps). When there are messages available in a chat, `clock`'s value is calculated based on the last received message in a particular chat: `last-message-clock-value + 1`. If there are no messages, `clock` is initialized with `timestamp`'s value.
`clock` value is used for the message ordering. Due to the used algorithm and distributed nature of the system, we achieve casual ordering which might produce counterintuitive results in some edge cases. For example, when one joins a public chat and sends a message before receiving the exist messages, their message `clock` value might be lower and the message will end up in the past when the historical messages are fetched.
The current protocol format is hardly upgradable without breaking backward compatibility. Because Transit is used in this particular way described above, the only reliable option is to append a new field to the Transit record definition. It will be simply ignored by the old clients.
Transit was initially chose for encoding, and Protobuf was added afterwards. This is partly due to the history of the protocol living inside of `status-react`, which is written in Clojurescript. In future versions of payload and data sync client specifications it is likely we'll move towards Protobuf only. See e.g. [Dasy](https://github.com/vacp2p/dasy) for a research proof of concept.
