A Repeatable Hardware Security Test Plan
Ad-hoc probing finds some bugs. A repeatable plan finds them consistently. A hardware security test plan is the structure that turns a clever afternoon at the bench into a method that covers the same ground every time, on every product, so nothing important gets skipped because the tester was tired or distracted.
Why a Plan Beats Improvisation
A skilled tester poking at a board will find real issues, but they will also miss things, and two testers, or the same tester on two days, will cover different ground. That inconsistency is the enemy of a trustworthy assessment. A plan makes coverage repeatable, so the result depends on the method rather than on who happened to run it.
A plan also makes findings comparable across products and over time. When every assessment runs the same phases, you can say with confidence that the debug interfaces were checked, the firmware was extracted and analyzed, and secure boot was tested. That structure is what lets a client trust that the absence of a finding means the area was actually examined.
Phase Zero: Scope and Safety
Before any probe touches the board, settle scope in writing: which units, which interfaces, what is in and out of bounds, and an explicit acknowledgement that a fragile device might be damaged or bricked. Hardware testing carries physical risk that software testing does not, and that risk has to be accepted before work begins.
Scoping also sets the depth. A black-box test with no documentation is a different effort from a white-box test with schematics and source. Agreeing on what the tester gets, and what success looks like, up front prevents the assessment from drifting and ensures the time is spent where the client most needs assurance.
Phase One: Reconnaissance
The first hands-on phase is identification: catalog the chips, find the processor, the storage, and the radios, read the markings, pull the datasheets, and map the buses between components. The output is a labeled board map that every later phase references.
- Identify the processor or SoC from its markings, then pull the datasheet
- Identify flash, eMMC, or NAND storage
- Identify the radios with an FCC ID lookup
- Locate candidate debug pads for JTAG, SWD, and UART
- Map the inter-chip buses such as SPI, I2C, and parallel
- Photograph both sides of the board at high resolution
Recon feels unglamorous, but skipping it is how assessments waste days probing the wrong part. A complete board map turns the rest of the plan from guesswork into targeted work.
Phase Two: Interface Discovery
With the map in hand, find and characterize the external and debug interfaces. Determine which are present, which are active, and which are locked, because that decides the easiest path in.
- UART located, baud detected, and console or shell reached, noting whether it is locked
- JTAG or SWD present and responding, noting RDP or auth locking
- Test points mapped to signals by continuity
- USB and other ports enumerated and fingerprinted
- Boot-mode strap pins identified
This phase frequently produces the highest-value findings on the whole assessment, because an open UART shell or a live debug port is a direct route in.
Phase Three: Firmware Extraction
Get the firmware by whatever path the device allows: a bootloader console dump, a debug-port read, or a chip-off read of the flash. The plan tries the cheapest method first and escalates, recording which methods worked, because that itself is a finding about how exposed the firmware is.
How easily the firmware comes off is as important as what is in it. A device that hands over its image through an open console has a different risk profile from one that requires desoldering a BGA. The plan captures both the image and the effort it took.
Phase Four: Firmware Analysis
With the image in hand, analyze it systematically, walking the same sub-checklist every time so nothing gets missed under time pressure.
- Bootloader identified, and secure boot confirmed present or absent
- Filesystem extracted and sensitive files reviewed
- Hardcoded credentials and private keys searched for
- Crypto usage reviewed, including modes, IVs, and key storage
- Update mechanism checked for signing and anti-rollback
- Debug hooks and undocumented services found
This is where most of the detailed findings come from. Deep in a disassembler it is easy to forget to check the update mechanism or to grep for keys; the list ensures every image gets the same thorough treatment.
Phase Five: Hardware Attacks
Where scope and threat model justify it, the plan includes the deeper hardware attacks: side-channel analysis, fault injection against secure boot or a debug lock, and bus sniffing for secrets in transit. These are time-consuming, so the plan gates them on the threat model. A consumer gadget may not justify a glitch campaign; a payment device or a safety-critical controller does, and deciding that in the plan keeps the effort proportional and the scope honest.
Phase Six: Network and Protocol Testing
A connected product’s radios and network services get their own phase: scan the open ports, test the web and API interfaces, examine the wireless protocols, and check the cloud-facing communication. A weakness reachable over the network is more exposed than one needing physical access, so findings here often rank highest, and running it as a defined phase ensures the radio and network surface gets the same systematic coverage as the silicon.
Document, Then Prioritize
The plan requires capturing evidence at each step, photos of the board and connections, command transcripts, dumps, and notes, while the work happens, not from memory afterward. A finding written as connect SWD to these pads, run this command, observe this result is one a developer can reproduce and confirm fixed; I think the debug port was open is not.
It all ends in a report that ranks findings by impact and reachability, explains each in terms a product team can act on, and gives concrete remediation. Ranking matters as much as finding: a report that lists twenty issues without priority leaves the team unsure where to start, so the unsigned firmware and the open debug port rise above the cosmetic ones and the fix budget goes where it reduces the most risk.
Keep It Living and Tailored
The plan itself is a versioned, living document, improved after each assessment. A new technique, a new class of finding, a step that proved valuable all get folded back in, so the method gets stronger over time and every product benefits from what the last one taught. Versioning also lets you state exactly what methodology an assessment followed, which matters for clients with compliance needs.
A good plan is a template, not a straitjacket. The phases stay constant, but their depth flexes with the product and its threat model, ideally built earlier from attack trees and trust boundaries. The model says what matters for this product; the plan ensures those things get tested systematically. That pairing is what makes an assessment both thorough and focused.
Where This Fits
A repeatable, threat-model-driven test plan is the backbone of every hardware penetration test and product security assessment I run. If you want your product assessed with a structured method that covers the same ground every time, that is the kind of work we do at Berkner Tech.
