There has been a continuous growth in the usage of number of IoT devices. These devices are subject to an increasing number of attacks which exploit their software vulnerabilities. We need a secure architectural design for cryptographic keys involved in both initial configuration (onboarding) and secure automatic updates of IoT devices. Low-level IoT devices have low computational capabilities and small memory size and are challenged to carry out desktop- and server-type public-key cryptographic operations, as needed for key establishment and authentication of software updates. We have designed and implemented a prototype to provide secure onboarding and update architecture and associated protocols for low-level IoT devices (8-bit). It uses elliptic curve cryptography (Curve25519), authenticated key establishment, and a known continuity-based key-locking mechanism that uses a public key embedded in current software image to verify the signature on software update. The design also addresses the scenario of transfer of update authority change.