wormhole/whitepapers/0009_guardian_key.md

Guardian Key Usage

Objective

• Describe how guardian keys are used and how message confusion is avoided.

Background

Message confusion could occur when a Guardian signs a message and an attacker replays that message elsewhere where it is interpreted as a different message type, which could lead to unintended behavior.

Overview

The Guardian Key is used to:

1. Sign gossip messages
   1. heartbeat
   2. governor config and governor status
   3. observation request
2. Sign Observations
   1. Version 1 VAAs
   2. Version 2 VAAs, i.e. Batch VAAs.

Detailed Design

Signing of gossip messages:

1. Prepend the message type prefix to the payload
2. Compute Keccak256Hash of the payload.
3. Compute ethcrypto.Sign()

Signing of Observations:

• v1 VAA: double-Keccak256(observation).
• v2 (batchVAA): double-Keccak256(version | Keccak256(hash1 | hash2 | ... | hash_n)), where | stands for concatenation.

Rationale

• Gossip messages cannot be confused with other gossip messages because the message type prefix is prepended.
• Gossip messages cannot be confused with observations because observations utilize a double-Keccak256 and the payload is enforced to be >=34 bytes.
• v2 VAAs cannot be confused as v1 VAAs because their payload when parsed as a v1 VAA is only 33 bytes, which does not constitute a valid observation.
• v1 VAAs cannot be confused as v2 VAAs because observations are longer than 33 bytes and hence do not constitute a valid v2 VAA body.