LoadSoft loads the private key from disk and creates the corresponding SoftKey.

SortTransferableInputsWithSigners sorts the inputs and signers based on the input's utxo ID.

To deduct transfer fee from total spend (output).

To create a new key SoftKey with a pre-loaded private key.

To create a new key SoftKey with a pre-defined private key.

Key defines methods for key manager interface.