This code was a rotational cipher, created to encrypt military communications by the city-state of
T'omba during long war with rival
Wijt. It remained uncracked for 7 years, despite several military dispatches falling into enemy hands. Eventually the
Gavrilites broke the cipher on behalf of Wijt, allowing them to bring the war to a successful conclusion.
Creation
The cipher was created by the military authorities of T'omba with a goal of protecting communications between the commanders naval squadrons operating on various branches of the
Fetr'andt Delta. It was a rotational cipher whose rotation number was given based on which of a few stock greetings the letter opened with.
The working of the cipher was a tightly controlled state secret. Even admirals and generals were not aware of its functioning. Instead, a small group of government scribes were trained in its use. Two of these scribes would be assigned to each military commander to read and write encrypted messages as necessary. These scribes carried a small vial of poison around their necks at all time and were instructed to commit suicide if captured by the enemy to safeguard the secret of the cipher.
Usage
The cipher proved its worth several times during the 7 year war between Wijt and T'omba. In particular during the siege of Rurk, when the besieged commander was coordinating with a relieving force to attack the besiegers simultaneously in both front and rear. 3 messengers were sent out from the besieged city, each bearing an identical encrypted copy of the plan. Two were captured along with their messages but the third made it through. As the besiegers could not read the letters, they were caught by surprise and routed by the combined forces of the garrison and relieving army the next day.
Cracking
Frustrated by their inability to capitalize on captured intelligence, the council of Wijt turned to a secretive scientific order known as the
Gavrilites for help. They were given copies of captured texts.
An early breakthrough came when they were trying to match characters to a planetary chart and someone suggested that perhaps the letters rotated around, just like the stars do in the night sky. This proved to be the case and the Gavrilites were able to brute-force the cipher. While this method worked, it was highly time consuming, taking a team of scribes a week to break a single message.
A second breakthrough occured when it was noticed that greetings were always highly formal and took only one of a few possible forms. By comparing these across some of the messages that had been brute-forced, they quickly realized that this was acting as a key for the rotation amount. This discovery allowed messages to be decrypted by a single scribe in only a few hours.
Aftermath
Decrypted enemy communications proved pivotal in bringing the war to a close in favor of Wijt. As a reward for their services, the Gavrilites were given several privileges as well as possession of the
Vijnul Tower in Wijt which they turned into their headquarters.
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