Implementation
TransactionBuilder build(seed, int index,
{String curve = 'ed25519', String hashAlgo = 'sha256'}) {
final KeyPair keypair = crypto.deriveKeyPair(seed, index, curve: curve);
final KeyPair nextKeypair =
crypto.deriveKeyPair(seed, index + 1, curve: curve);
final Uint8List address =
crypto.hash(nextKeypair.publicKey, algo: hashAlgo);
this.address = address;
previousPublicKey = keypair.publicKey;
previousSignature =
crypto.sign(previousSignaturePayload(), keypair.privateKey);
return this;
}