Digital certificates are signed by a server's private key and installed at lock controllers that restrict access to physical resources. The server's public key is distributed to lock controllers and to mobile electronic devices operated by users who are given access to the physical resources. Lock-access data is digitally signed by the server's private key and provided to mobile electronic devices to facilitate access. The lock controller validates lock-access data and grants access conditionally based on time, version, and/or identity data provided within lock-access data. The use of certificates reduces the need to rely on a security scheme specific to the network. Lock controllers can also broadcast status notifications, so that updates and log data can be securely communicated with the server using mobile electronic devices as a proxy. The system is highly scalable, as each lock controller need not track the full scope of access permissions.