Master Viewing Key (MVK) for Solana Address

Protocol Description

The Master Viewing Key for a user's primary Solana address, denoted $k_{\text{MVK}, \text{SOL}}$, is derived directly from the master seed $S_M$ using the Poseidon hash function as a PRF.

$$k_{\text{MVK}, \text{SOL}} \triangleq \text{Poseidon}( S_M, \text{EncodeAsFieldElement}(\text{"MVK-Solana-Address"}) )$$

The output $k_{\text{MVK}, \text{SOL}}$ is a single field element in $\mathbb{F}_p$. This MVK must be registered on-chain and is immutable thereafter.

Key Derivation Process

1. Input: Master seed $S_M$ (32 bytes)
2. Domain Separation: String $"MVK-Solana-Address"$ encoded as a field element
3. Hash Function: Poseidon hash function acting as a PRF
4. Output: Single field element $k_{\text{MVK}, \text{SOL}}$ in $\mathbb{F}_p$

On-Chain Registration

The $k_{\text{MVK}, \text{SOL}}$ must be registered on-chain before any deposit transactions can be made. This registration:

• Enables Compliance: Required for Tier 3 compliance mechanism
• Immutable: Cannot be changed once registered
• Public Commitment: Creates a public commitment to the MVK without revealing it
• Transaction Prerequisite: Must be registered before deposits

Security Analysis

Security Proof: Unlinkability of the Solana MVK

Goal: $k_{\text{MVK}, \text{SOL}}$ must be computationally indistinguishable from a random element in $\mathbb{F}_p$ and unlinkable to $S_M$.

Assumption: The Poseidon function, when one of its inputs is kept secret, behaves as a secure PRF.

Argument: The derivation is a direct application of a PRF where $S_M$ is the secret key. The output $(k_{\text{MVK}, \text{SOL}})$ is computationally indistinguishable from a uniformly random element chosen from its range $(\mathbb{F}_p)$.

Properties

• Unlinkable: Cannot be traced back to the master seed
• Pseudorandom: Appears as a random field element
• Immutable: Once registered, cannot be changed
• Compliance Ready: Enables regulatory compliance features
• Single Purpose: Specifically for the user's primary Solana address