[adrianvrj]

Summary

STRK20 private transfers for Starknet wallets, run inside the Cavos vault.

• SNIP-44 viewing key (account-leaf-v1) derived from the account's stark key, verified against the spec's normative vectors and 2,000 random cross-checks with Starkzap's implementation.
• Inside the vault only. The viewing key, notes and witnesses never cross the postMessage boundary (SNIP-44 "Wallet and dapp boundary"). The page never chooses the pool, prover or discovery service: they come from the app's Cavos settings (privacy in /api/vault/policy, keyed sepolia / mainnet).
• Before every operation the vault reads get_public_key(account) from the pool and refuses if a different key is registered. It never registers a replacement.
• Submission goes through the paymaster privacy relay (apply_action / invoke_and_apply_action), so the user's account never appears on-chain. Quotes are refused when the fee recipient is not allowed, when the fee exceeds maxFee or the pool's own fee, or when the approval typed data is tampered with.
• Spends go through the existing vault policy. Deposit, transfer and withdraw ask for confirmation according to the app's limits; unknown tokens are flagged.
• Page API: CavosStarknet.privacy.{status, balance, register, deposit, transfer, withdraw}.
• starknet bumped to ^10.5.0. v10 hashes proofFacts into the invoke hash, which proof-carrying transactions need. No other code changed for the bump.
• Dependency: @starkware-libs/starknet-privacy-sdk is an optional peer dependency, loaded with a dynamic import. It is bundled into the vault IIFE.
  • It is published on GitHub Packages, so .npmrc maps the scope and CI authenticates with GITHUB_TOKEN (packages: read).
  • The vault host bundle grows to about 1.2 MB.

Test plan

• npx tsc --noEmit
• npx jest: 447 passed, 2 skipped. Coverage:
  • register → deposit → transfer → balance → withdraw end to end on the SDK's in-memory pool, directly and through the real VaultClient over a MessageChannel;
  • nothing secret crosses the channel (the viewing key and account key are checked in hex, decimal and padded form);
  • relay quote and typed-data tampering is refused;
  • the vault asks for confirmation according to policy.
• npm run build.
• Signing on Sepolia through Starkzap with the vault signer, before the privacy work: address equality, paymaster deploy, and a sponsored transfer (0x274c8256…c8296f, SUCCEEDED).
• A private transfer against the real pool. Pending: the paymaster with privacy support needs to be deployed, along with the cavos-web settings.

Related

• cavos-labs/paymaster: upstream private transactions plus GasTank charging.
• cavos-labs/cavos: per-app privacy settings and webhook.

Release

Merging publishes @cavos/kit@0.4.3.

Note for integrators: starknet.js v10's Account no longer extends Provider. Call provider methods through wallet.account.provider.* rather than on wallet.account directly.

Apps that keep the key in the page and want privacy pass privacySdk: () => import("@starkware-libs/starknet-privacy-sdk") together with privacy. The npm entries never import the SDK, so apps that do not use privacy build without it.