To protect against physical and side-channel attacks, circuit assemblies may mount a main processor opposite of a cryptographic processor such that traces between the two processors are hidden in a substrate. Another substrate defining a cavity may be mounted on the bottom of the substrate to enclose the cryptographic processor and prevent physical access without disrupting the cryptographic operations. Voltage converters with integrated inductors may also be included in the cavity to generate electromagnetic noise that will disrupt the sensitive equipment used in side-channel attacks. An electromagnetic shield may be sputtered on top of the main processor to block electromagnetic sniffing attacks while still allowing the processor to be coupled with a heat sink.