Methods and apparatus for large scale distribution of electronic access control clients. In one aspect, a tiered security software protocol is disclosed. In one exemplary embodiment, a server electronic Universal Integrated Circuit Card (eUICC) and client eUICC software comprise a so-called ''stack'' of software layers. Each software layer is responsible for a set of hierarchical functions which are negotiated with its corresponding peer software layer. The tiered security software protocol is configured for large scale distribution of electronic Subscriber Identity Modules (eSIMs).