Promising, Contract, Evaluation

In the opening sections of the Genealogy of Morals, II, Nietzsche expresses respect for Promising as a contractual arrangement.  However, the genealogy of that evaluation is uncertain.  It does not come from Master Morality, since, as he poses it in GM II, 17, "he who is by nature 'master' . . . what has he to do with contracts?"  Nor is it plausible that the respect is derived from an evaluation of Hobbesian' Contractualism, because the latter is embedded in the context of a 'war of all against all', a condition that, according to Human, All Too Human, #45, is "base".  A likelier precedent is Lockeian Contractualism, which Nietzsche evokes when characterizing the Active Forgetfulness that is the precondition of Promising as a "tabula rasa" in GM, II, 1.  However, that Contractualism constitutes a Democracy, which Nietzsche never advocates.  So, his evaluation of the practice of Promising seems to have no obvious ancestor in his doctrine.