In cryptography , a cipher (or cypher ) is an algorithm for performing encryption or decryption —a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment . To encipher or encode is to convert information into cipher or code. In common parlance, "cipher" is synonymous with " code ", as they are both a set of steps that encrypt a message; however, the concepts are distinct in cryptography, especially classical cryptography .
29-716: Rasterschlüssel 44 (abbr. RS 44) was a manual cipher system, used by the German Wehrmacht during the Second World War . The cipher was designed by the astronomer and sometime cryptographer Walter Fricke while working as a conscript in Section IIb, of Group 2 of OKW/Chi and introduced in March 1944 and the Allied forces codebreakers had considerable difficulties in breaking it. Cryptanalysis , if successful, generally required
58-525: A Rail Fence Cipher ). For example, "GOOD DOG" can be encrypted as "PLLX XLP" where "L" substitutes for "O", "P" for "G", and "X" for "D" in the message. Transposition of the letters "GOOD DOG" can result in "DGOGDOO". These simple ciphers and examples are easy to crack, even without plaintext-ciphertext pairs. In the 1640s, the Parliamentarian commander, Edward Montagu, 2nd Earl of Manchester , developed ciphers to send coded messages to his allies during
87-470: A 40 letter crib (known plaintext) and some two weeks, making the tactical information outdated before it could be exploited. The combination of strength and ease of use made RS 44 an ideal hand cipher. The cipher is a transposition based grille cipher, consisting of a grid with 25 columns and 24 rows. Each row contains 10 randomly placed white cells (to be filled with text) and 15 black cells. The columns are labeled with shuffled digraphs and numbers and
116-795: A carefully constructed code could reduce message lengths enormously. Early codes were typically compilations of phrases and corresponding codewords numbering in the tens of thousands. Codewords were chosen to be pronounceable words to minimize errors by telegraphers, and telegrams composed of non-pronounceable words cost significantly more. Regulations of the International Telegraph Union evolved over time; in 1879, it mandated coded telegrams only contain words from German, English, Spanish, French, Italian, Dutch, Portuguese, or Latin, but commercial codes already frequently used nonsense words. By 1903 regulations were changed to allow any pronounceable word no more than ten letters long. Another aim of
145-519: A cipher to encrypt a message. Without knowledge of the key, it should be extremely difficult, if not impossible, to decrypt the resulting ciphertext into readable plaintext. Most modern ciphers can be categorized in several ways: Originating from the Arabic word for zero صفر (ṣifr), the word "cipher" spread to Europe as part of the Arabic numeral system during the Middle Ages. The Roman numeral system lacked
174-506: A shorter message. An example of this is the commercial telegraph code which was used to shorten long telegraph messages which resulted from entering into commercial contracts using exchanges of telegrams . Another example is given by whole word ciphers, which allow the user to replace an entire word with a symbol or character, much like the way written Japanese utilizes Kanji (meaning Chinese characters in Japanese) characters to supplement
203-422: A skunk!"), or AYYLU ("Not clearly coded, repeat more clearly."). The first telegraphic codes were developed shortly after the advent of the telegraph, and spread rapidly: the first codebook was in use by 1845. In 1854, one eighth of telegrams transmitted between New York and New Orleans were written in code. Cable tolls were charged by the word, and telegraph companies counted codewords like any other words, so
232-471: A symmetric key algorithm (e.g., DES and AES), the sender and receiver must have a shared key set up in advance and kept secret from all other parties; the sender uses this key for encryption, and the receiver uses the same key for decryption. The design of AES (Advanced Encryption System) was beneficial because it aimed to overcome the flaws in the design of the DES (Data encryption standard). AES's designer's claim that
261-504: A unique transposition for each message, making multiple anagramming very difficult. Cipher Codes generally substitute different length strings of characters in the output, while ciphers generally substitute the same number of characters as are input. A code maps one meaning with another. Words and phrases can be coded as letters or numbers. Codes typically have direct meaning from input to key. Codes primarily function to save time. Ciphers are algorithmic. The given input must follow
290-573: A wool dealer argued that an error by a Western Union telegrapher cost $ 20,000 due to misread instructions. The Supreme Court subsequently ruled Western Union was liable only for the cost of the message, $ 1.15. Examples of commercial codes include the ABC Telegraphic Code , Bentley's Second Phrase Code , Lieber's Standard Telegraphic Code (1896), Phillips Code (1879 and later), Slater's Telegraphy Code (1916), Western Union Universal Codebook (1907) and Unicode (1889). In codes such as
319-429: Is calculated from the minutes of the message time, the letter count of the message text and the randomly chosen column of the start cell. The message key contains the start position of the text in the grid, designated by the column and header digraphs. The digraphs for the message key are encoded with the letter conversion table and then included in the message header. The secret variable start cell and first column ensure
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#1732906167917348-438: Is one of the earliest known cryptographic systems. Julius Caesar used a cipher that shifts the letters in the alphabet in place by three and wrapping the remaining letters to the front to write to Marcus Tullius Cicero in approximately 50 BC. Historical pen and paper ciphers used in the past are sometimes known as classical ciphers . They include simple substitution ciphers (such as ROT13 ) and transposition ciphers (such as
377-481: Is possible to create a secure pen and paper cipher based on a one-time pad , but these have other disadvantages. During the early twentieth century, electro-mechanical machines were invented to do encryption and decryption using transposition, polyalphabetic substitution, and a kind of "additive" substitution. In rotor machines , several rotor disks provided polyalphabetic substitution, while plug boards provided another substitution. Keys were easily changed by changing
406-785: The Acme Code and the ABC Code , were published and widely used between the 1870s and the 1950s, before the arrival of transatlantic telephone calls and next-day airmail rendered them obsolete. Numerous special-purpose codes were also developed and sold for fields as varied as aviation, car dealerships, insurance, and cinema, containing words and phrases commonly used in those professions. These codes turned complete phrases into single words (commonly of five letters). These were not always genuine words; for example, codes contained "words" such as BYOXO ("Are you trying to weasel out of our deal?"), LIOUY ("Why do you not answer my question?"), BMULD ("You're
435-416: The ABC Code , code words could contain blanks. For example, in the "Freight and tonnage requirements" section, ANTITACTE means "Mozambique, loading at not more than two places, to ____, steamer for about ____ tons general cargo at ____ per ton on the d/w capacity to cargo". The telegrapher would then fill in the three parameters: the destination, the number of tons, and the price per ton. The regulations of
464-585: The English Civil War . Simple ciphers were replaced by polyalphabetic substitution ciphers (such as the Vigenère ) which changed the substitution alphabet for every letter. For example, "GOOD DOG" can be encrypted as "PLSX TWF" where "L", "S", and "W" substitute for "O". With even a small amount of known or estimated plaintext, simple polyalphabetic substitution ciphers and letter transposition ciphers designed for pen and paper encryption are easy to crack. It
493-511: The International Telegraph Convention distinguished between "code telegrams", which it describes as "those composed of words the context of which has no intelligible meaning", and "cipher telegrams", which it describes as "those containing series of groups of figures or letters having a secret meaning or words not to be found in a standard dictionary of the language". Cipher telegrams were subject to higher tolls. Codes such as
522-463: The cipher's process to be solved. Ciphers are commonly used to encrypt written information. Codes operated by substituting according to a large codebook which linked a random string of characters or numbers to a word or phrase. For example, "UQJHSE" could be the code for "Proceed to the following coordinates." When using a cipher the original information is known as plaintext , and the encrypted form as ciphertext . The ciphertext message contains all
551-453: The common means of modern cipher cryptanalytic attacks are ineffective against AES due to its design structure.[12] Ciphers can be distinguished into two types by the type of input data: In a pure mathematical attack, (i.e., lacking any other information to help break a cipher) two factors above all count: Since the desired effect is computational difficulty, in theory one would choose an algorithm and desired difficulty level, thus decide
580-473: The concept of zero , and this limited advances in mathematics. In this transition, the word was adopted into Medieval Latin as cifra, and then into Middle French as cifre. This eventually led to the English word cipher (minority spelling cypher). One theory for how the term came to refer to encoding is that the concept of zero was confusing to Europeans, and so the term came to refer to a message or communication that
609-450: The difficulty of managing a cumbersome codebook . Because of this, codes have fallen into disuse in modern cryptography, and ciphers are the dominant technique. There are a variety of different types of encryption. Algorithms used earlier in the history of cryptography are substantially different from modern methods, and modern ciphers can be classified according to how they operate and whether they use one or two keys. The Caesar Cipher
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#1732906167917638-441: The information of the plaintext message, but is not in a format readable by a human or computer without the proper mechanism to decrypt it. The operation of a cipher usually depends on a piece of auxiliary information, called a key (or, in traditional NSA parlance, a cryptovariable ). The encrypting procedure is varied depending on the key, which changes the detailed operation of the algorithm. A key must be selected before using
667-890: The key length accordingly. Claude Shannon proved, using information theory considerations, that any theoretically unbreakable cipher must have keys which are at least as long as the plaintext, and used only once: one-time pad . Commercial code (communications) In telecommunication , a commercial code is a code once used to save on cablegram costs. Telegraph (and telex ) charged per word sent, so companies which sent large volumes of telegrams developed codes to save money on tolls. Elaborate commercial codes which encoded complete phrases into single words were developed and published as codebooks of thousands of phrases and sentences with corresponding codewords. Commercial codes were not generally intended to keep telegrams private, as codes were widely published; they were usually cost-saving measures only. Many general-purpose codes, such as
696-546: The native Japanese characters representing syllables. An example using English language with Kanji could be to replace "The quick brown fox jumps over the lazy dog" by "The quick brown 狐 jumps 上 the lazy 犬". Stenographers sometimes use specific symbols to abbreviate whole words. Ciphers, on the other hand, work at a lower level: the level of individual letters, small groups of letters, or, in modern schemes, individual bits and blocks of bits. Some systems used both codes and ciphers in one system, using superencipherment to increase
725-469: The rotor disks and the plugboard wires. Although these encryption methods were more complex than previous schemes and required machines to encrypt and decrypt, other machines such as the British Bombe were invented to crack these encryption methods. Modern encryption methods can be divided by two criteria: by type of key used, and by type of input data. By type of key used ciphers are divided into: In
754-404: The rows with digraphs. The key sheet also contains two letter substitution alphabets to encode place names, prior to encryption , and a letter conversion alphabet to encode digraphs. The text is written in the grid, starting from a randomly chosen position, row by row, from left to right. The ciphertext is taken column by column, following the numbering of the columns. The first column to be taken
783-423: The security. In some cases the terms codes and ciphers are used synonymously with substitution and transposition , respectively. Historically, cryptography was split into a dichotomy of codes and ciphers, while coding had its own terminology analogous to that of ciphers: " encoding , codetext , decoding " and so on. However, codes have a variety of drawbacks, including susceptibility to cryptanalysis and
812-500: The telegraph codes was to reduce the risk of misunderstanding by avoiding having similar words mean similar things. Codes were usually designed to avoid error by using words which could not be easily confused by telegraph operators. Telegrapher errors could sometimes cause serious monetary damages, which in one instance resulted in the United States Supreme Court case Primrose v. Western Union Telephone Company , in which
841-462: Was not easily understood. The term cipher was later also used to refer to any Arabic digit, or to calculation using them, so encoding text in the form of Arabic numerals is literally converting the text to "ciphers". In casual contexts, "code" and "cipher" can typically be used interchangeably; however, the technical usages of the words refer to different concepts. Codes contain meaning; words and phrases are assigned to numbers or symbols, creating
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