MESSAGE-FORMATTING

Field	Value
Name	Message Formatting
Slug	89
Status	raw
Category	Standards Track
Editor	Marcin Pawlowski
Contributors	Youngjoon Lee [email protected], Alexander Mozeika [email protected], Álvaro Castro-Castilla [email protected], Filip Dimitrijevic [email protected]

Timeline

2026-05-28 — d45eed2 — Chore: mirror blochain specs into github/mdbook (#347)

Revision History

Version	Changes	Date
1.0.0	Initial revision.	2026-04-09

Introduction

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

In this document we are reusing notation from Notation.

Overview

The message contains a header and a payload. The header informs the protocol about the version of the protocol and the payload type. The message contains a drop or a non-drop payload. The length of a payload is fixed to prevent adversaries from distinguishing types of messages based on their length.

Construction

Message

The Message is a structure that contains a public_header, private_header and a payload.

class Message:
      public_header: PublicHeader,
      private_header: Private_Header,
      payload: bytes

Public Header

The public_header must be generated as the outcome of the [1.0.0] Message Encapsulation Mechanism.

The public_header is defined as follows:

class PublicHeader:
        version: byte,
      public_key: PublicKey,
      proof_of_quota: ProofOfQuota,
      signature: Signature

Where:

version=0x01 is version of the protocol.
public_key is $K^{n}_i$ , a public key from the set $\mathbf K^n_h$ as defined in the Message Encapsulation spec.
proof_of_quota is $\pi^{K^{n}_i}_{Q}$ , a corresponding proof of quota for the key $K^{n}_i$ from the $\mathbf K^n_h$ it also contains the key nullifier.
signature is $\sigma_{K^{n}_{i}}(\mathbf {h|P}_i)$ , a signature of the concatenation of the $i$ -th encapsulation of the payload $\mathbf P$ and the private header $\mathbf h$ , that can be verified by the public key $K^{n}_{i}$ .

Private Header

The private_header must be generated as the outcome of the [1.0.0] Message Encapsulation Mechanism.

The private header contains a set of encrypted blending headers $\mathbf h = (\mathbf b_1,...,\mathbf b_{h_{max}})$ .

private_header: list[BlendingHeader]

The size of the set is limited to $\beta_{max}=3$ BlendingHeader entries, as defined in the Global Parameters.

The BlendingHeader ( $\mathbf b_l$ ) is defined as follows:

class BlendingHeader:
      public_key: PublicKey,
      proof_of_quota: ProofOfQuota,
      signature: Signature,
      proof_of_selection: ProofOfSelection
      is_last: byte

Where:

public_key is $K^{n}_{l}$ , a public key from the set $\mathbf K^n_h$ .
proof_of_quota is $\pi^{K^{n}_l}_{Q}$ , a corresponding proof of quota for the key $K^{n}_l$ from the $\mathbf K^n_h$ it also contains the key nullifier.
signature is $\sigma_{K^{n}_{l}}(\mathbf {h|P}_l)$ , a signature of the concatenation of $l$ -th encapsulation of the payload $\mathbf P$ and the private header $\mathbf h$ , that can be verified by public key $K^{n}_{l}$ .
proof_of_selection is $\pi^{K^{n}_{l+1},m_{l+1}}_{S}$ , a proof of selection of the node index $m_{l+1}$ assuming valid proof of quota $\pi^{K^{n}_{l}}_{Q}$ .
is_last is $\Omega$ , a flag that indicates that this is the last encapsulation.

Payload

The payload must be formatted according to the [1.0.0] Payload Formatting. The formatted payload must be generated as the outcome of the [1.0.0] Message Encapsulation Mechanism.

Maximum Payload Length

The Max_Payload_Length parameter defines the maximum length of the payload, which for version 1 of the Blend Protocol is fixed as Max_Payload_Length=34003. That is, 34kB for the payload body (Max_Body_Length) and 3 bytes for the payload header. More information about payload formatting can be found in [1.0.0] Payload Formatting.

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