System Architecture

01. Overview

02. Anchor Protocol

The identity registry is governed by a secure Anchor program. It manages the mapping of human-readable handles to cryptographic public keys.

#[program]

pub mod key_registry {

    pub fn register_username(ctx: Context, username: String) -> Result<()> {

        let user_account = &mut ctx.accounts.user_account;

        user_account.owner = ctx.accounts.owner.key();

        user_account.username = username.to_lowercase();

        Ok(())

    }

}

Each username exists as a Program Derived Address (PDA). This design prevents handle-space collisions and ensures that each handle can only be initialized once, effectively creating a decentralized name service for messaging.

03. Whisper Mechanism

Communication is achieved through "Whisper Transactions" — tiny SOL transfers carrying encrypted payloads in their memo data.

04. Fee Payer

To enable a frictionless user experience, Key operates a robust Fee Payer Network. This off-chain service manages the operational treasury required to fund user activity.

• Automated Underwriting

  The API uses sophisticated rate-limiting and spending caps (0.01 SOL/day per user) to ensure the sustainability of the free-forever model while preventing malicious drain.

• Non-Custodial Design

  While the Fee Payer signs for gas, it never has access to identity keys or message content. It is a blind service, underwriting the costs of sovereignty without compromising it.

05. Sustainability