Security Analysis

Iterative Response Testing for Access Control

One of the classic exercises in RF security is evaluating the resilience of consumer access control systems, specifically fixed-code and early rolling-code garage door openers operating in the 300-390 MHz ISM bands. While capturing and replaying a fixed code is trivial, automating the testing of the code space is where Mycelium truly shines.

In this walkthrough, we will demonstrate how to use Mycelium's Mutate_Data and Increment_Variable directives to systematically transmit every possible code in a 12-bit keyspace.

Step 1: Setting up the Transmitter

We'll configure a tool using the `ISM_Generic` protocol (included in the IoT Mission Pack) utilizing OOK (On-Off Keying) modulation. Most legacy gate openers operate near 315 MHz or 390 MHz.

Step 2: Defining the Loop Variable

Instead of manually writing a script to generate thousands of payloads, we can use Mycelium's built-in variable engine to track our progress through the keyspace.

Step 3: Payload Generation and Transmission

Next, we need to load a base payload, inject our current `key_index` into it, and transmit it over the air.

Step 4: The Stopping Condition

Since a 12-bit keyspace has 4,096 possible combinations, we want the tool to stop automatically once it has exhausted the list.

Execution Flow

digraph { graph [bgcolor="transparent" fontname="Inter" rankdir=TB pad=0.4] node [fontname="Inter" fontsize=12 fontcolor="#e2e8f0" style=filled fillcolor="#1a1033" color="#8b5cf6" penwidth=1.5 margin="0.2,0.15" shape=box] edge [color="#8b5cf6" fontcolor="#a78bfa" fontname="Inter" fontsize=10 arrowsize=0.8] start [label="Start Tool" shape=ellipse] init [label="Initialize key_index = 0"] check [label="key_index >= 4096?" shape=diamond fillcolor="#2d1b69"] done [label="Stop Execution" shape=ellipse] load [label="Load Base Payload (0x0000)"] inject [label="Inject key_index into Payload"] transmit [label="Modulate OOK and Transmit"] wait [label="Wait 50ms"] increment [label="Increment key_index by 1"] start -> init -> check check -> done [label="Yes"] check -> load [label="No"] load -> inject -> transmit -> wait -> increment -> check }

Conclusion

Upon typing execute, Mycelium will rapidly iterate from 0 to 4095, injecting each value into the generic ISM frame structure, modulating it to OOK, and transmitting it at 315 MHz. What used to require a custom GNU Radio flowgraph and a Python orchestrator script is now fully contained within a few lines of Mycelium directives to test the resilience of the target system.



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