For game purposes, codes are split into three groups: pre-machine codes; codes created by cipher machines; and computerized cryptography.
All references to modifiers for “deciphering” or “decrypting” assume the character lacks the key to the code and tries to “break” it. If he has the key, decoding a message is so simple a task it rarely even requires a roll.
PRE-MACHINE CODES
Long before the existence of cipher machines and computers, people created codes by hand or using simple tools. It’s in this period that the termi- nology and methodology of cryptography devel- oped. Broadly speaking, one can divide encryption into two types: codes and ciphers.
A code is a system of encryption in which specific symbols, words, or phrases stand for other words or phrases. For example, “blue bonnet” might mean “artillery,” and “barnyard” might stand for “Paris, France.” The string of code-words may be utterly meaningless, but the cleverest codes involve placing the seemingly innocent code-words in the midst of innocuous text. Determining the true meaning of a code is virtually impossible unless the decoder has
access to the codebook (in which case it’s child’s play) or enough messages with enough context to make it possible to determine correlations.
A cipher is a method of encryption in which each letter in the original message is replaced by some other letter, number, symbol, or what have you. The system for enciphering the message is known as the key. Unlike codes, which are rigid and unchangeable, most ciphers are flexible (sometimes enormously so). The key allows for changes or forms of variation that make the decipherer’s job much more difficult.
Substitution And Transposition Ciphers
All ciphers fall into one (or both) of two catego- ries: substitution ciphers and transposition ciphers. Substitution Cipher: The most basic of ciphers, in which each letter is replaced by another letter or number according to the key, but doesn’t change its position within the word. A simple child’s cipher, such as A = 1, B = 2, C = 3, and so on, is an example of a substitution cipher. Many of the other types of ciphers listed below are, fundamentally, just elabo- rate variations on the substitution cipher.
Even if he lacks a cipher’s key, a cryptanalyst can often solve a substitution cipher via frequency
analysis — determining the frequency with which
letters appear in a given language, and then applying that information to the cipher’s symbols to make it statistically simpler to guess what each one stands for. The use of nulls — additional, meaningless char- acters scattered throughout the message — partly counteracts this, as does deliberate misspelling; it also works better on long messages than short ones.
Substitution ciphers fall into two general categories: monoalphabetic, in which the cipher remains the same throughout the message (e.g., the homophonic substitution cipher); and poly-
alphabetic, in which the cipher changes one or
more times throughout the message (e.g., the VigenPre cipher).
A simple substitution cipher counts as a Very Simple code (modifier of +2 or better). More elab- orate ones are Simple, Average, or Complex. Transposition Cipher: This form of encoding involves changing the position of a letter or word within a message, but not the letter’s or word’s meaning. The transposition takes place according to the key, so that the recipient of the message can easily decipher it. For example, in a transposition cipher in which every two letters are reversed, “river” becomes “irevr.” A transposition cipher counts as a Very Simple or Simple code (modifier of +0 or better).
Specific Types Of Codes And Ciphers
Some specific types of codes and ciphers include:
Auto-key Generation Code: In this form of substi- tution cipher, the letter used to stand for the true letter depends on the letter preceding it. For exam- ple, suppose a character wants to encrypt the word “river.” The R is in plain text. R is the 18th letter in
the Latin alphabet. The next letter to encrypt is I, so the encoder counts 18 letters from I, yielding Z. Z
is the 26th letter in the alphabet, and 26 letters from
V is U. Thus, “river” ends up as RZUZQ. An auto- key generation code cipher counts as a Simple code (modifier of +0 or +1).
Book Cipher: A cipher in which a book, portion of a book, or some other piece of text provides the key. A book cipher counts as a Very Complex code (modifier of -5 or worse), but the GM may reduce the penalty if the character has clues regarding which book or document is the key (e.g., he has access to the encoder’s library, he makes a Deduction roll after learning some rel- evant facts, or the like).
Caesar-Shift Substitution Cipher: A substitu- tion cipher in which each letter of the message is replaced with the letter x places down in the alphabet; x is a number between 1 and 25. The classic example uses x = 3, so that “river” becomes “ulyhu.” A Caesar-shift cipher counts as a Very Simple or Simple code (modifier of +0 or better). Homophonic Substitution Cipher: A form of sub- stitution cipher in which each plaintext letter has several possible substitutions (the number usu- ally varies based on the frequency of the letter). A homophonic substitution cipher counts as an Aver- age code (modifier of -2).
Keyword Code: A keyword code (or, more accu- rately, keyword cipher) uses a word or phrase with ten letters or words, none of which repeat. The letters or word represent the numerals 1 through 9 and 0. The letters or words can be used to write phone numbers, letters of the alphabet (via a simple substitution cipher), and the like, though to the uninitiated they look like meaningless strings of letters. Keyword codes are popular among crim- inals, since they’re easy to remember. A keyword cipher counts as a Very Simple or Simple code (modifier of +0 or better).
Nomenclator: A system of encoding that relies mainly on ciphering, but with some codewords involved as well. A nomenclator counts as an Aver- age code (modifier of -1 or -2).
Onetime Pad Cipher: Toward the end of the First World War, American cryptographers found ways to restore the VigenPre cipher (see below) to useful- ness by making the key structureless and extending its length to the length of the message. The keys are meaningless strings of letters listed on sheets on a pad. The key on each sheet is unique and used only once. Both sender and receiver have a copy of the pad. After encrypting and decrypting a message with the key on the first piece of paper on the pad, the sender and receiver both destroy that sheet. The randomness of the key makes it mathematically impossible to decipher the code via cryptanalysis. In fact, the possibility exists that anyone trying brute- force cryptanalysis will actually “read” a seemingly true message in the encrypted text that isn’t there! However, the onetime pad cipher system suffers from practical difficulties — logistical problems relating to manufacturing and distribution, vulner- ability to the loss or theft of the pad — so it was hardly ever actually used. Only in situations where
the risks are acceptable and the logistical difficulties easily overcome can a onetime pad cipher function effectively. For example, one is (or has been) used in secure communications between the presidents of the United States and the Soviet Union. A onetime pad cipher counts as a Very Complex code; creating one requires a Cryptography roll at -5 (or worse); deciphering one is impossible.
Pigpen Cipher: A monoalphabetic substitution cipher that uses tic-tac-toe and X-shaped grids to generate symbols to replace letters. It’s been used for centuries; for example, the Freemasons of the 1700s employed it to keep their records secure. A pigpen cipher counts as a Very Simple or Simple code (modifier of +0 or better).
Playfair Cipher: A relatively simple substitution cipher that uses a keyword, a five-by-five square of letters, and a system of breaking messages into digraphs (two-letter combinations). A Playfair cipher counts as a Very Simple or Simple code (modifier of +0 or better).
Rail Fence Transposition Cipher: A cipher in which the alternating letters of a message are written on two lines, one above the other, and then the two lines of gibberish are joined into one long line of gibberish. Decoding it is simply a matter of know- ing or deducing where the two lines join. A rail fence transposition cipher counts as a Very Simple or Simple code (modifier of +0 or better).
Superencipherment: Double ciphering, i.e., run- ning a cipher through another cipher algorithm. Performing a superencipherment requires a Cryp- tography roll with the combined modifiers for the two types of ciphers used; deciphering one requires a Cryptography roll with the combined penalties of the two types of ciphers used, plus an additional -2. Vigenère cipher: Invented around the year 1560, the VigenPre cipher is a series of 26 separate cipher alphabets, each one Caesar-shifted. A key- word determines which cipher alphabet is used to encode/decode each letter of the message, making cryptanalysis by frequency analysis impossible. VigenPre ciphers remained unbreakable until 1854, when Charles Babbage devised a way to crack them (though he didn’t publish it, so it became known as the Kasiski Test after the man who did in 1863). A VigenPre cipher counts as a Very Com- plex code (modifier of -5 or worse).
Rules For Pre-Machine Codes
In most cases, you can resolve attempts to encrypt or decrypt a “handmade” code or cipher using the normal Skill Versus Skill Contest rules and the modifiers outlined above. See below regarding base times.
Language
Of course, breaking a code doesn’t confer knowledge of the language in which the plaintext is written. In fact, if the cryptanalyst cannot speak and read the plaintext language, he may have trouble deciphering the cipher, since awareness of linguistic structure and the like may provide clues to cracking the code.
For that matter, a language itself, if untrans- lateable by others, can serve as a foolproof code. The Navajo “code talkers” who helped America with battlefield communications in World War II are a perfect example. The Axis powers had no way to translate the complex Navajo language, making it an ideal method for passing secret mes- sages; it was never “broken.”
CIPHER MACHINES
Cryptologists eventually learned to use machines to aid in the cryptographic process. The earliest known machine is a form of cipher
disk, two metal disks with the alphabet inscribed
around the edge of each, invented in fifteenth century Italy. Cipher disks were used in many situations and conflicts, including the American Civil War (and in the twentieth century for chil- drens’ “decoder ring” toys).
The Enigma Machine
In 1919 the German Arthur Scherbuis invented the Enigma machine, a sort of highly- advanced electronic form of the cipher disk, and revolutionized cryptology. (Inventors in the Neth- erlands, Sweden, and the United States all invented similar machines in the 1919-27 period, but like Enigma they were all commercial failures with the business community.) The device, which wasn’t much larger than a typewriter, had over 10 quadril- lion possible keys, making brute-force cryptanalysis effectively impossible. All Enigma required for use was that both the sender and receiver have one of the machines and a codebook indicating the initial scrambler setting. Thanks to Enigma, the German military, which had been cryptologically backward during World War I, had the most secure cryptog- raphy in the world during much of the Pulp era... ...until a disaffected German sold the plans for building an Enigma machine to the French in 1931. France’s ally Poland employed a bril-
liant mathematician named Marian Rejewski, who found a way to determine the day and mes- sage settings the Germans used. His efforts were negated in 1938 when the Germans complicated the workings of Enigma and once again rendered it secure. But in the summer of 1939, the Poles supplied their methods and breakthroughs to the French and British so the work of once again defeating Enigma could continue.
At the newly-formed Government Code & Cypher School at Bletchley Park, the British set to work to break Enigma a second time. With more resources and manpower than the Poles, they were soon able to do so by building on the Poles’ accom- plishments. Although the Germans advanced the sophistication of Enigma throughout the war, the British, whose codebreakers included the likes of Alan Turing, kept pace with them. The transpar- ency of German communications due to the efforts of Bletchley Park was one of the decisive factors in the Allied victory.
The Allies had their own cipher machines, which the Germans did not break. The difference is that the Germans used their machines in ways which gave cryptanalysts clues that enabled them to break the code, whereas the British and Ameri- cans didn’t make such mistakes. Enigma could easily have been unbreakable... if used with full and proper security protocols.
Cipher Machine Rules
To operate a simple cipher machine, such as an early cipher disk, a character need only make a Cryptography roll (if a roll is necessary at all). Operating a complex cipher machine like Enigma requires a dedicated Professional Skill (e.g., PS: Use Enigma Machine).
A cipher machine’s strength and sophistica- tion is rated by its Cryptography roll. If the person doing the encoding uses the machine properly, the penalty listed in the Cipher Machine Cryptography table applies to attempts to decrypt the message without the key. If he fails, the listed penalty still applies, but is reduced by the number of points he failed the roll by. For example, ordinarily an advanced cipher machine (21-) imposes a penalty of -16 on decryption attempts. If the operator fails his roll by three, then the penalty becomes only -13.
When someone tries to decrypt a message enciphered by a cipher machine, he engages in a Skill Versus Skill Contest against the results of the machine’s roll; the machine’s “strength of encryption” penalty modifies his roll. For example, suppose that the Nichtwahr cipher machine has Cryptography 18-. The operator makes his PS: Use Nichtwahr Machine roll, so he then rolls 3d6 for the machine, getting a result of 11. The machine has made its roll by 7, and due to the strength of its encryption imposes a base -8 penalty. Therefore someone who wants to break the cipher without the key has to make his own Cryptography roll... at a -15 penalty (the base -8, plus 7 for the amount the roll succeeded by).
Unlike computers (see below), cipher machines generally can only encrypt messages. They can, of course, decrypt messages they create