Silhouette Webapp

The Silhouette webapp is the frontend for interacting with the other Silhouette system components. It plays a key role in ensuring that individual order flows and balances are only visible to the trader.

Core Capabilities

1. Authenticate Securely: Connect a preferred wallet.
2. Manage UI Encryption Keys: The webapp handles the generation and secure local storage of a dedicated X25519 key pair used for encrypting communications with the secure enclave.
3. Deposit: Initiate a direct transfer on HyperCore from the trader's wallet to the Silhouette smart contract's HyperCore wallet.
4. Submit Encrypted Communications: Construct and transmit orders, cancellations, and withdrawal requests, encrypted end-to-end between the browser and the secure enclave.
5. Monitor Trading Activity: View order history, balances, and status updates.

Enabling Private Trades

Silhouette achieves order flow privacy through a cryptographic protocol orchestrated by the webapp:

1. Authentication: A session is initiated by authenticating with a preferred wallet. The primary wallet's private keys remain under the exclusive control of the trader's wallet.

2. UI Encryption Key Establishment:

   • The webapp generates a unique X25519 key pair (ui_keypair). This key pair is distinct from any authentication-related session keys.
   • The private component (ui_private_key) is stored securely within the browser's IndexedDB, namespaced by the connected account address and network ID. This key never leaves the browser.
   • The public component (ui_public_key) is registered with the Silhouette smart contract, associating it with the authenticated wallet address.
   • This X25519 key pair is persistent, allowing the user to decrypt their historical data. Future enhancements may include optional encryption of this key at rest in IndexedDB.

3. Secure Channel with Enclave:

   • The webapp retrieves the enclave's pre-published X25519 public key (enclave_public_key) from the Silhouette smart contract.
   • Using the ui_private_key and enclave_public_key, the webapp computes a shared secret via the X25519 Diffie-Hellman (ECDH) algorithm (e.g., using tweetnacl).
   • This shared secret is then typically used with a Key Derivation Function (KDF), like HKDF, to derive a symmetric key suitable for AES-GCM encryption.

4. Encrypted Order Submission:

   • When an order is submitted, the webapp encrypts order details using the derived symmetric key (AES-GCM) and a unique nonce.
   • The resulting cipher-text and nonce are transmitted to the Silhouette smart contract. Order details remain opaque to the blockchain.

5. Enclave Processing:

   • The secure enclave monitors the Silhouette smart contract for new encrypted orders.
   • For a specific order, the enclave retrieves the corresponding ui_public_key from the Silhouette smart contract.
   • Using its own private key and the ui_public_key, the enclave independently computes the identical shared secret.
   • The enclave uses this shared secret and the received nonce to decrypt the order.
   • Decrypted orders are processed within the enclave's confidential matching engine.

Webapp Security Model

The webapp focuses on protecting trading intentions and ensuring user control over primary assets:

• Wallet Key Isolation:

  • Primary wallet private keys are never exposed to the webapp. All operations requiring the primary wallet's signature are delegated to the user's connected wallet software.
  • Direct access to on-chain assets (e.g., withdrawals to arbitrary addresses) is controlled by the primary wallet, not the UI's encryption keys.

• UI Encryption Key Security:

  • The X25519 private key (ui_private_key) used for encrypting communications is generated and stored exclusively within the browser's IndexedDB, protected by the browser's same-origin policy.
  • This key is persistent to allow users to access their historical encrypted data. Users should ensure their browser environment and device are secure.
  • Compromise of the ui_private_key would allow an attacker to:
    • Decrypt any past and future messages exchanged between the user's browser and the enclave that were encrypted with this key.
    • Potentially submit new encrypted messages (e.g., trades) to the enclave as if they were the user, depending on the enclave's authorization model beyond just decryption.
  • However, such a compromise does not directly expose the user's primary wallet private keys or allow unauthorized movement of on-chain assets from the primary wallet.

• End-to-End Encryption:

  • Sensitive trading data (order type, size, and price) is encrypted using AES-GCM (derived from the X25519 shared secret) before leaving the browser.
  • Only the secure enclave, capable of independently deriving the same shared secret and symmetric key, can decrypt this information.
  • Neither Hyperliquid blockchain validators nor any other intermediaries can view raw order details, including Silhouette.