Military and sensitive commercial UAVs transmit classified imagery, targeting data, and C2 commands that demand NSA Suite B cryptography (AES-256, ECDSA, SHA-384). The Communication Encryption PCB is a dedicated cryptographic co-processor board that sits in-line between the flight computer and the RF transceiver, encrypting all outgoing data and decrypting all incoming traffic with hardware-accelerated ciphers. This board must achieve FIPS 140-2 Level 3 certification, which imposes physical security requirements that directly shape the PCB design.
Cryptographic Engine Architecture
The encryption board is built around a hardware crypto accelerator — typically an FPGA with dedicated AES-GCM cores or a secure microcontroller like the Microchip CEC1702. The engine supports full-duplex encryption at data rates up to 100 Mbps, with sub-100 µs latency. Key architectural features include:
Dual independent data paths: Separate Tx (encrypt) and Rx (decrypt) chains with independent DMA engines to prevent cross-channel leakage.
True Random Number Generator (TRNG): A hardware TRNG based on avalanche diode noise, not a pseudo-random algorithm, generates initialization vectors (IVs) and session keys. The TRNG analog front-end requires a shielded PCB zone with guard rings to prevent deterministic interference.
Physical Unclonable Function (PUF): SRAM-based PUF derives a unique device key from power-up SRAM state, eliminating the need to store a master key in non-volatile memory.
Tamper Detection & Response
FIPS 140-2 Level 3 requires the board to detect physical tampering and zeroize cryptographic keys within milliseconds. The PCB implements a multi-layer tamper detection mesh:
Inner-layer tamper mesh: A serpentine trace on an internal layer covers the entire secure zone. Any drill attempt shorts this trace to ground or VCC, triggering an instant key erase.
Enclosure tamper switches: Four normally-closed mechanical tamper switches (at board corners) are wired in series. Opening the enclosure breaks the circuit and asserts the tamper input on the security processor.
Temperature/voltage monitoring: ADC inputs continuously monitor board temperature and supply voltage. Excursions outside the normal operating windows are treated as potential fault-injection attacks and trigger a key zeroization.
Active shield: A wire-bonded or flex-circuit active shield over the crypto processor carries a randomized signal; any probe penetration disturbs the signal and is detected within one clock cycle.
Physical Isolation of Secure Domain
The encryption PCB is physically partitioned into a red side (plaintext data from the flight computer) and a black side (ciphertext to the RF transceiver), with the crypto engine forming the boundary. A 2.5 mm routed isolation slot completely separates red and black ground planes, with all signals crossing the boundary passing through the crypto engine's dedicated red/black I/O pins. No copper pour or trace bridges the isolation slot at any layer.
Secure Key Storage & Battery Backup
Long-term keys stored in battery-backed SRAM (BBRAM) within the secure element require a primary lithium coin cell and a backup supercapacitor with automatic switchover. The BBRAM supply rail includes a voltage supervisor that asserts a tamper condition if the battery voltage drops below 2.0V. A dedicated PCB copper pour — isolated from all other domains — forms the secure battery supply plane.
Conclusion
The Communication Encryption PCB is as much a physical security device as it is an electronic one. Every copper trace, every via, and every layer of the stackup contributes to the tamper-evident envelope that protects cryptographic keys. Superb Tech fabricates encryption PCBs with inner-layer tamper meshes, routed isolation slots, and secure battery domains — all manufactured to IPC Class 3 with full continuity verification of every tamper trace.
