Generate a signature proving funds sent to <address> in <txid>, optionally with a challenge string <message>, using either the transaction secret key (when <address> is not your wallet's address) or the view secret key (otherwise), which does not disclose the secret key.
Generate a signature proving that you own at least this much, optionally with a challenge string <message>. If 'all' is specified, you prove the entire sum of all of your existing accounts' balances. Otherwise, you prove the reserve of the smallest possible amount above <amount> available in your current account.