Type42 class

BRC-42 (BSV "type-42") key derivation.

Pure crypto — no isolate, no UI, no key storage. This is the shared primitive behind NodeCast's broker-as-verifier pay-per-view gate (see overnode_v2's docs/nodecast/ARCHITECTURE.md §6): the payer derives a per-invoice payment destination C from the creator's public key without the creator's private key, and the creator later recomputes the matching spend key.

Construction — must match bitcoin-sv/bsv-blockchain/go-sdk and the Tier-0 harness (overnode_v2's docs/nodecast/tier0) byte-for-byte:

sharedSecret = (priv · pub) point, serialized COMPRESSED (33 bytes)
t            = HMAC-SHA256(key = sharedSecretCompressed, msg = utf8(invoiceNumber))
childPub  C  = recipientPub + t·G
childPriv c  = (recipientPriv + t) mod N

Verified against the official BRC-42 test vectors — see test/crypto/type42_test.dart. This is net-new crypto we own and it sits on the money path (R6): keep it test-vector-pinned.

All elliptic-curve math is routed through dartsv's own secp256k1 instance (t·G is computed via a private key, never a foreign generator) to avoid silent cross-instance curve mismatches.

Properties

hashCode → int

The hash code for this object.

no setter, inherited

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

noSuchMethod(Invocation invocation) → dynamic

Invoked when a nonexistent method or property is accessed.

inherited

toString() → String

A string representation of this object.

inherited

Operators

operator ==(Object other) → bool

The equality operator.

inherited

Static Methods

deriveChildPrivate(SVPrivateKey recipientPriv, SVPublicKey senderPub, String invoiceNumber) → SVPrivateKey

Child private key c = (recipientPriv + t) mod N — the spend key matching deriveChildPublic.

deriveChildPublic(SVPublicKey recipientPub, SVPrivateKey senderPriv, String invoiceNumber) → SVPublicKey

Child public key C = recipientPub + t·G.

sharedSecret(SVPrivateKey priv, SVPublicKey pub) → Uint8List

ECDH shared secret between priv and pub, serialized as a COMPRESSED secp256k1 point (33 bytes).

tweak(List<int> sharedSecretCompressed, String invoiceNumber) → BigInt

Per-invoice tweak scalar t = HMAC-SHA256(key = sharedSecretCompressed, msg = utf8(invoiceNumber)), interpreted as a big-endian integer.