Cryptography

Cryptography, also known as Cryptology, is the practice and study of techniques for converting information into a form for secure communication or storage in the face of a known or potential adversary.

Due to the covert, sensitive or hidden nature of certain subjects concerning them, various aspects of cryptography are utilized on both magic and science sides.

Etymology
The prefix crypto-, present in both cryptography and cryptology, is derived from the Greek kryptos/kruptós/κρυπτός (meaning "hidden" or "secret"). For the respective suffixes, -graphy derives from -graphia/gráphō/γράφω (meaning "writing"), and -logy derives from -λογία/-logia ("study/account of").

Two terms in Japanese that can be used to refer to many subjects within the field of cryptography/cryptology are angō (暗号) and kaidoku (解読).

Principles
There are various methods of encryption and different types of cipher. Two examples of basic cipher types are a (one of which is utilized with the ), where the positions of characters are moved to produce a different permutation of a text's characters, and a  (of which, the  is a basic example), where characters are substituted for different characters. In modern times, the advance of science has given rise to new methods of encryption, including applications of random number generation and properties of (applications of the latter,  and otherwise, being referred to as ).

The Kaesaru-shiki Angō (カエサル式暗号), named after and used by the famous Roman general in private correspondence, is a basic substitution cipher which often used as an initial foundation leading into more complex encryptions. With it, the letters in the text are substituted with the respective letters a set number of places from them along the alphabet, forwards or backwards.

There are various tools which have been used to support cryptographic processes, from simple mechanical devices to modern computers. A very early example used in is the Sukyutarē-shiki (スキュタレー式), a cylinder around which a strap of single letters is wrapped. Using a type of transposition cipher, when wrapped around the sideways cylinder vertically, the letters on the strap line up to spell out the intended message horizontally, one which isn't apparent from the order of the letters on the strap when it is unwrapped.

One variant of cryptography is, which involves concealing a hidden message within another message or an object. Rather than just protecting the contents of a message, steganography also involves concealing the fact that a secret message is being sent.

Given the use of codes in the magic side, large counter-magical organizations such as Necessarius may have decoding specialists among their ranks, such as Orsola Aquinas and Sherry Cromwell, the latter specializing in codes hidden in paintings. The position of Cancellarius in the Roman Catholic Church, once held by Aureolus Izzard, was one said to be involved in decoding witchcraft and finding countermeasures.

Background
Cryptography has been used in simple forms since antiquity, with examples including the used in  and the, a substitution cipher named after and used by Roman general  of Rome in private correspondence.

Due to the hidden nature of the magic side, forms of cryptography have been utilized at various points throughout its history. Many grimoires and magical texts are written in code (the infamous the Book of the Law among them),     and people like the Rosicrucians have used a form of code to concealed magical messages within paintings, music and other works of art.

One notable cryptographer who was also involved in the occult, was, a German abbot and polymath whose students included and. Two of his famous cryptographic works are the three-volume and the five-volume. One of the ciphers in the latter was utilized in the that were involved in the founding of the Golden Dawn by William Wynn Westcott and Samuel Liddell MacGregor Mathers.

At some point, an absolute encryption contest was held in Academy City, with the random number encryption program Omega Secret winning the contest, subsequently gaining a reputation for being practically unbreakable. The company Montgolfier was previously involved in quantum cryptography work.

Orsola Aquinas Rescue Arc
Orsola Aquinas's supposed discovery of a way to decipher the Book of the Law, from attempts at decoding incomplete copies of the book in order to find a way to destroy the grimoire, is what resulted in the Roman Catholic Church targeting her. During the subsequent conflict over her, it emerged that what she found was one of the fake codes written into the book's construction and not the true method of decoding it.

Toaru Majutsu no Index Light Novel Volume SS2
On the third Friday of September, while hacking into the Bank for an unknown reason, Misaka Mikoto found the data inside the system becoming encrypted at a rate she couldn't keep up with even with her powers, and deduced that it was the work of Omega Secret from the random manner of encryption.

Toaru Majutsu no Index SS: Agnese's Magic Side Work Experience
While investigating a possible connection between the recent incidents they had resolved, Agnese Sanctis, Lucia and Angelene experienced frustration in dealing with ciphers on top of many languages when reading grimoires in the Anglican remote database in Zurich. Later, during the attack on the Guild's base, they found that the Guild was using a  for its encryptions, rather than a  as they expected from a group dating from ancient Greece, a fact they would use in figuring out how the Guild had changed with the times from Greek to Roman to Christian, their thinking and their goals.

Coronzon Arc
During the events surrounding the Crowley's Hazard invasion of the United Kingdom, the recreated William Wynn Westcott utilized a spell, verbally invoking a coded text he held, fragments said to reveal power when read using methods of ’s, and referred to the knowledge of the Golden Dawn's beginning.

Christmas Eve Arc
During the events on December 24th, Misaka Mikoto and Misaka 10032 had a brief competition over who could crack Maidono Hoshimi's phone, only to be surprised when Index beat them to the passcode - an incident which would later be referred to in a discussion about the vulnerability of electronic protection and encryption to magic.

Los Angeles Arc
During the events in Los Angeles on December 26th, Othinus had a discussion with Kamijou Touma about the vulnerability of firewalls and other forms of electronic protection, even quantum encryption, to magic, referencing how Index was previously able to break a phone's password even without magic, and raising the possibility that the Academy City forces' unmanned weapons may have been turned against them.

The practice of hiding messages (such as a recipe for the Philosopher's Stone) in paintings, and the possible simplicty of the code by using symbols only known to an intended recipient (such as the sun representing gold and a pelican for the stone) was also referenced while trying to solve a message left on Melzabeth Grocery's smartwatch. Stiyl Magnus also considered that the Citrinitas spell would have required the decoding of a German original grimoire.

Post-Handcuffs Arc
During Anna Sprengel and Aradia's conversation on the legends of the Transcendents, when the former was officially joining the Bridge Builders Cabal and touring their base, texts coded, analyzed and rearranged were talked of, along with letters, notes, texts from correspondence lessons, and urban legends.

Sisters Arc
Uiharu received a call from Mikoto asking for any information about the clone's passcode "ZXC741ASD852QWE963"; soon enough, Uiharu told Mikoto that it is a clearance code for high-level information.

Jailbreaker Arc
After agreeing to cooperate with Uiharu, Aohoshi Suzuran handed her an encrypted USB stick with data from the facility where Shundan Kimi and her friends were experimented on. Uiharu easily broke through the encryption, finding information concerning the true nature of Kimi's ability.

Trivia

 * Although not a cryptographical device itself, the design of the John's Pen Remote Control was influenced by the device reminding Haimura Kiyotaka of the from the, a device whose name is said to derive from cryptology's crypto- and codex - using the "science of cryptology" to hide a codex, whose design in turn also bears similarities to historical wheel ciphers and wheel-based encryption devices, such as the.