The vibrating needle in the guardroom was no longer an alarm; it was a signature. Kael watched the iron lever twitch in a rhythmic, repeating sequence that defied the chaotic fluctuations of a failing battery or a loose connection. This was a "Hand-Tap"—a deliberate attempt by someone on the other end of the line to feed a ghost-signal into Ashfall's nervous system. The Duke's unknown engineer was testing the line, attempting to find the resonant frequency that would keep the relay closed while their sappers moved in for a second, more coordinated strike.
The "grit" of this chapter was the transition from physical engineering to mathematical warfare. Kael realized that a simple "on-off" circuit was a liability. To secure his communications and his perimeter, he needed to embed a layer of logic into the current. He needed a code that could not be mimicked by simple tapping. He initiated the development of the Binary Cipher Key.
"If they can mimic the pulse, we must change the pulse's meaning," Kael explained to the gathered Telegraphers. The workshop was filled with the smell of ozone and the scratch of charcoal on slate. "From this hour, the Gray Fang and the Intake do not send steady signals. They send 'Packets.' A sequence of short and long pulses that correspond to a mathematical prime."
The technical challenge was the Mechanical Encoder. The human variable—the speed and consistency of a telegrapher's hand—was too prone to error under the stress of a raid. Kael designed a series of rotating brass cylinders, etched with specific patterns of conductive and non-conductive slots. When the cylinder was turned by a hand-crank, it acted as an automated switch, sending a perfectly timed "key" down the line. To change the code, the operators simply swapped the cylinders.
This was the birth of Protocol-Based Security. If the receiver in the guardroom didn't detect the specific mathematical rhythm of the "Key Cylinder," the alarm would sound, even if the current remained steady. Kael was no longer just monitoring for a break in the wire; he was monitoring for a break in the logic.
Socially, this created a profound rift within the "Information Citizens." The older telegraphers, who prided themselves on their manual "hand," felt threatened by the brass cylinders. They saw the automation as a devaluation of their specialized skill. Kael addressed this by introducing the Cryptographic Tier. He tasked the most advanced students with the creation of the cylinder patterns themselves—turning them from simple "tappers" into "Logic Architects."
A systemic failure occurred during the implementation of the first "Rotating Key." The cold of the Gray Fang caused the brass cylinders to contract, leading to "Signal Jitter"—the contacts wouldn't seat perfectly, causing the receiver to misinterpret the code as a breach. For six hours, the barony was locked in a false-alarm cycle, the bells ringing every twelve minutes as the mechanical "logic" failed to align with the physical reality.
Kael spent the night at the Gray Fang summit, his hands bleeding as he filed the brass slots by lamplight to account for the thermal contraction. He realized that a rigid code was as dangerous as a rigid bridge. He engineered a Tolerance Buffer—a secondary magnetic coil in the relay that would allow for a five-percent deviation in the pulse timing. It was a "fuzzy logic" solution, allowing the system to ignore the "noise" of the environment while still detecting the "signal" of the key.
The moment of the "Mathematical Duel" came at midnight. The needle began to vibrate again, but this time, the "Ghost Engineer" was sophisticated. They were sending a perfect imitation of the morning's code. But Kael had already swapped the cylinders to the "Prime Sequence."
Because the incoming signal didn't match the new logic, the alarm triggered instantly.
Kael didn't fire the magnesium flares this time. He utilized the Relay-Triggered Counter-Charge. By reversing the polarity of the Galvanic Line and dumping the entire reserve of the battery bank into the wire, he sent a high-voltage surge back toward the intruder. In the riverbed, there was a sudden, bright blue flash as the "Ghost Engineer's" own tapping tool was short-circuited. A cry of pain echoed through the gorge, followed by the sound of someone scrambling away through the rocks.
Kael held the brass cylinder. He had won the first battle of the ciphers, but the cost was a new kind of exhaustion. He had moved the conflict from the mud and the water into the abstract realm of numbers and time.
"They're learning, Elms," Kael said, looking at the charred contact point on the relay. "They have a machine of their own now. This wasn't a sapper; this was an architect. We need to stop thinking about walls and start thinking about Information Redundancy. If they can't break our code, they'll try to 'jam' our air."