Owner: @Marcin Pawlowski

Reviewers: 🟢@Youngjoon Lee 🟢@Alexander Mozeika 🟢@Álvaro Castro-Castilla

Introduction

This document defines an implementation-friendly specification of the Payload Formatting, which is introduced in the Formatting section.

Overview

The payload contains a header and a body. The header informs the protocol about the way the body must be handled. The body contains a raw message (data/proposal or cover message). The payload must be of a fixed length to prevent adversaries from distinguishing types of messages based on their length. Therefore, shorter messages must be padded with random data.

Construction

Payload

The Payload is a structure that contains a header and a body.

class Payload:
	  header: Header,
	  body: bytes

Header

The header is a structure that contains a body_type and a body_length.

class Header:
  	body_type: byte,
	  body_length: uint16

Type

We define the following values of the body_type:

• body_type=0x00, informs that the body contains a cover message.
• body_type=0x01, informs that the body contains a data message.

Any other value of type means that the message was not decapsulated correctly and must be discarded.

Length

We define the body_length as uint16 (encoded as little-endian). Therefore, the theoretical limit of the length of the body is 65535 bytes. The body_length must be set to the length of the body of the payload message (body_length=len(raw_message)).