emino on Nostr: sequenceDiagram actor User as User / Wallet UI participant SECURITYKEY as Biometric ...

sequenceDiagram
actor User as User / Wallet UI
participant SECURITYKEY as Biometric Hardware<br/>(FIDO2 authenticator)
participant ENCLAVE as Secure Enclave<br/>Share A
note right of ENCLAVE: Signing happens securely here,<br/>ensuring no RAM leak.
participant HSM as Cloud HSM<br/>Share B
participant BTC as Bitcoin Network

%% ─── Spend flow ───
User->>SECURITYKEY: 1️⃣ WebAuthn “get assertion” (physical touch)
SECURITYKEY-->>User: hmac-secret + signature

User->>ENCLAVE: 2️⃣ Unlock Share A (using hmac-secret)
ENCLAVE-->>User: Partial Signature A

User->>HSM: 3️⃣ Sign request + Security Key assertion proof
HSM-->>User: Partial Signature B

User->>User: 4️⃣ Combine Sig A + Sig B (FROST threshold)

User->>BTC: 5️⃣ Broadcast Taproot tx
BTC-->>User: Tx confirmed

Note over User,BTC: Full private key is **never reconstructed** Security Key touch and Biometrics is always required.