The
Vyandrin Cipher, from the
Tretalleri words
vyandë meaning "secret", and
rina meaning "word", is the cipher used by the
Dominion's intelligence agents to encrypt communications of moderate importance, such as mission briefs and non-urgent progress reports. While the
existence of the cipher itself was known to the public for much of the Dominion's history, the actual mechanisms of the cipher remained a closely-guarded secret until the development of
Hæmographology not only allowed for more secure communications, but also the creation of faster, more secure ciphers.
The relative obscurity of the vyandrin cipher was viewed as a matter of national security for the Dominion. As such, the strictest and deadliest blood magic compulsion, a
Blood Obligation, was placed upon those who used and studied the cipher. Under the terms of the Blood Obligation, individuals who had knowledge of the cipher were barred from disclosing and even merely hinting at its mechanisms in any way to anyone bar
confirmed members of the Dominion intelligence agency. Indeed, this proved to be vital as scholarly investigation of similar ciphers found ways to break the fundamental principles that formed the base of the vyandrin cipher many millennia before it fell out of use.
Invention
The vyandrin cipher was invented by a group of linguists and mathematicians tasked by the
Grand Rookery to create a means of securing communication of military importance in
233.12 NL after twenty-three years of work. Prior to the invention of the vyandrin cipher, the Dominion had relied on coded messages, substitution ciphers, and, in foreign lands, the use of the formal form of Tretalleri.
A number of other important cryptological tools arose from the development of the vyandrin cipher, namely what is known as the
jeda velelutë, "tall rectangle" in Tretalleri, a table of shifted alphabets used for the other important concept that was invented, the polyalphabetic cipher. A precursor version of the vyandrin cipher, the malan cipher, named after its inventor and leader of the commissioned team,
Malan a'Diren, was presented to the Grand Rookery in
227.12 NL but found to be too simple.
The malan cipher entered the public sphere, with Dominion authorization, shortly thereafter in ca.
400.12 NL.
Mechanisms
The vyandrin cipher is a polyalphabetic cipher that uses an inverted version of the jeda velelutë, which allows for the same operation to be used to encrypt and decrypt the text. In this sense, the vyandrin cipher is a simple polyalphabetic cipher that is essentially a reciprocal (meaning the same operation is used to encrypt the text and decrypt it) version of the malan cipher. However, while the malan cipher uses a single keyword repeated as many times as necessary to cover the length of the plaintext to form the keystream, the vyandrin cipher uses a randomised keystream.
To accomplish this, the vyandrin cipher is used with a set of 81 keywords of varying length, some of which are nonsensical, that must be memorized by all agents who use it. Each keyword is assigned multiple numerical values that must also be memorized. Whenever an agent wishes to encrypt some text, they are to select keywords at random, appending them to the end of the keystream until the keystream is as long as the plaintext. In the event that the last word of the keystream makes it longer than the plaintext, the keystream is truncated until it is exactly the length of the plaintext.
In order to encode the order of the keywords used to generate the keystream, each agent must memorize a given integer
N. For each keyword, the agent is to select one of its associated numeric values at random, which we shall call
K. At the end of the message, the agent must then record the result of
K mod
N, repeating the process until the order of the keywords used to create the keystream has been properly encoded.
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