Seed Identity

Anky v2 uses EVM seed-based identity. A seedphrase generates a wallet on the device. The backend only ever sees the derived wallet address and signed messages. Never the seed.

How It Works

On the Device (iOS App)

1. User creates or imports a BIP-39 seedphrase
2. The app derives an EVM wallet (secp256k1) from the seed
3. The wallet address becomes the user's identity

Authentication Flow

Device                          Server
  │                               │
  │  POST /swift/v2/auth/challenge
  │  { wallet_address: "0x..." }  │
  │──────────────────────────────▶│
  │                               │ Generate random challenge
  │  { challenge: "Sign this..." }│ Store in auth_challenges
  │◀──────────────────────────────│ with expiry
  │                               │
  │  Sign challenge with          │
  │  private key (EIP-191)        │
  │                               │
  │  POST /swift/v2/auth/verify   │
  │  { wallet, signature,         │
  │    challenge }                 │
  │──────────────────────────────▶│
  │                               │ Verify EIP-191 signature
  │                               │ Find/create user
  │                               │ Consume challenge
  │  { session_token: "..." }     │ Mint bearer session
  │◀──────────────────────────────│
  │                               │
  │  All subsequent requests:     │
  │  Authorization: Bearer <token>│
  │──────────────────────────────▶│

Child Wallet Derivation

Child identities are derived from the parent's seed on-device:

Parent seed → Parent wallet (m/44'/60'/0'/0/0)
           → Child 1 wallet (m/44'/60'/0'/0/1)
           → Child 2 wallet (m/44'/60'/0'/0/2)
           → ...

The server stores child_profiles.derived_wallet_address but never computes it. The device tells the server "this child wallet belongs to this parent wallet" and the server trusts the relationship because the parent authenticated.

Privacy Properties

• Seedphrase: Never leaves the device. Never sent to the server.
• Private key: Never leaves the device. Only used to sign challenges.
• Wallet address: Public. Used as the identity key.
• Writings: Keyed by wallet address in both SQLite and the file archive.
• Children: Derived wallets are computed on-device, stored on-server as associations only.

Why Not OAuth/Privy?

v1 uses Privy (OAuth-style). v2 moved to direct seed auth because:

1. No dependency on Privy's servers — if Privy goes down, v2 auth still works
2. Deterministic identity — the same seed always produces the same wallet. No account recovery, no email, no phone number.
3. Child derivation — you can't derive child wallets from an OAuth token
4. Philosophical alignment — the user owns their identity by holding their seed, not by having an account in someone else's database