Client SDK

The Shroud Network client SDK is a TypeScript library that handles all client-side operations: key management, note handling, proof generation, and transaction construction.

Modules

Module	Purpose
KeyManager	Baby Jubjub keypair generation, derivation from wallet signature
NoteManager	Create, store, encrypt, and track notes locally
MerkleTreeSync	Reconstruct full Merkle tree from on-chain events
ProofGenerator	Compute witness + Groth16 proof via snarkjs WASM
TransactionBuilder	Orchestrate full flows: select note → proof → submit
MemoEncryptor	ECDH on Baby Jubjub + AES-256-GCM for encrypted memos

Note structure

interface Note {
  amount: bigint;
  blinding: bigint;
  secret: bigint;
  nullifierPreimage: bigint;
  ownerPublicKey: [bigint, bigint];
  leafIndex: number;
  noteCommitment: bigint;
  pedersenCommitment: [bigint, bigint];
  nullifier: bigint;
  spent: boolean;
  tokenAddress: string;
  createdAtBlock: number;
}

Proof generation

All ZK proofs are generated locally in the browser using snarkjs:

const { proof, publicSignals } = await snarkjs.groth16.fullProve(
  witness,
  "transfer.wasm",     // WASM witness generator
  "transfer_final.zkey" // proving key
);

Proof generation takes under 1 second on modern hardware.

Encrypted memos

When you transfer tokens, the recipient needs to know their note details. This is communicated via encrypted memos in the transaction calldata:

1. Sender generates an ephemeral Baby Jubjub keypair
2. ECDH shared secret with recipient's public key
3. AES-256-GCM encryption of note data
4. Recipient scans events and trial-decrypts with their private key

If decryption succeeds (GCM auth passes), the note is for them. If it fails, it's for someone else.