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Crypto services

The cryptographic primitives the SDK builds on. Each is a service you can use independently or get via a session.

PoseidonHashService​

  • Construct: await PoseidonHashService.create(), async because it loads circomlibjs's WASM.
  • Method: hash(inputs: Hex[]) returns Hex.
  • Used by: commitment derivation, nullifier derivation, every Merkle root inside circuits.
  • Browser and Node: same API both sides.

CryptoService​

  • Construct: new CryptoService().
  • Methods:
    • generateEphemeralKeyPair(): fresh X25519 keypair.
    • ecdh(privKey, pubKey): X25519 ECDH shared-secret derivation.
    • encrypt(plaintext, sharedSecret) / decrypt(ciphertext, sharedSecret): symmetric encryption layered over the ECDH output.
    • generateSecret(): 48 random bytes reduced to a BN254 scalar (RFC 9380) (used for noteSecret, depositSecret).
    • deriveKeysFromSignature(config): the three account private keys plus the X25519 viewing public key, derived from a 65-byte ECDSA signature.
    • derivePaymentRequestKeyPair(viewingPrivateKey, ownerAddress, paymentId): deterministic X25519 keypair for a payment request (HKDF-SHA256). It is re-derivable on demand, so the private key never needs persisting.

NoteComputationService​

  • Wraps: PoseidonHashService and CryptoService for note-specific math.
  • Methods:
    • computeNoteAddressHash(ownerAddress, noteSecret)
    • computePrecommitment(noteAddressHash, tokenId, value)
    • computeLabel(precommitment, depositSecret)
    • computeFullCommitment({noteAddressHash, tokenId, value, label})
    • computeNullifier(privateNullifyingKey, commitment)
    • computeAuthDigest(privateRevocableKey)

WitnessPreparationService​

Builds the full input set the circuits need from your note and chain state. Used internally by ProofService, and rarely a direct dependency for callers.

ProofService​

Wraps a Groth16 prover (snarkjs under the hood) with a circuit-artifacts loader. Called by TransactOrchestrator to actually generate proofs.

Sources: v2-monorepo/packages/sdk/src/services/