Techniques in electronic systems, such as in systems including a processing chip and one or more external memory chips, provide improvements in one or more of system security, performance, cost, and efficiency. The processing chip includes immutable hardware enabled to securely boot one or more CPUs of the processing chip to execute code stored in a non-volatile one of the external memory chips, and to update the code. An update to the code is written to a portion of one of the external memory chips that is not accessible to the CPUs, and the immutable hardware copies the update to the non-volatile memory chip. The update is encrypted with a public portion of a key possessed by an entity sending the update, and a private portion of the key, used to decrypt code stored in the non-volatile memory chip, is unique to and solely possessed by the processing chip.