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43-398: 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

86-530: 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

129-560: A Caesar cipher is often incorporated as part of more complex schemes, such as the Vigenère cipher , and still has modern application in the ROT13 system. As with all single-alphabet substitution ciphers, the Caesar cipher is easily broken and in modern practice offers essentially no communications security . The transformation can be represented by aligning two alphabets; the cipher alphabet

172-436: A Caesar shift, which means they can produce the same ciphertext with different shifts. However, in practice the key can almost certainly be found with at least 6 characters of ciphertext. With the Caesar cipher, encrypting a text multiple times provides no additional security. This is because two encryptions of, say, shift A and shift B , will be equivalent to a single encryption with shift A + B . In mathematical terms,

215-529: 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

258-524: A codebook of 30,000 code groups superencrypted with 30,000 random additives. The book used in a book cipher or the book used in a running key cipher can be any book shared by sender and receiver and is different from a cryptographic codebook. In social sciences, a codebook is a document containing a list of the codes used in a set of data to refer to variables and their values, for example locations, occupations, or clinical diagnoses. Codebooks were also used in 19th- and 20th-century commercial codes for

301-589: A codebook system was by Gabriele de Lavinde in 1379 working for the Antipope Clement VII . Two-part codebooks go back as least as far as Antoine Rossignol in the 1800s. From the 15th century until the middle of the 19th century, nomenclators (named after nomenclator ) were the most used cryptographic method. Codebooks with superencryption were the most used cryptographic method of World War I. The JN-25 code used in World War II used

344-461: A cyclic pattern that might be detected with a statistically advanced version of frequency analysis. In April 2006, fugitive Mafia boss Bernardo Provenzano was captured in Sicily partly because some of his messages, clumsily written in a variation of the Caesar cipher, were broken. Provenzano's cipher used numbers, so that "A" would be written as "4", "B" as "5", and so on. In 2011, Rajib Karim

387-498: A more sophisticated code program called Mujahedeen Secrets "because 'kaffirs', or non-believers, know about it, so it must be less secure". The Caesar cipher can be easily broken even in a ciphertext-only scenario . Since there are only a limited number of possible shifts (25 in English), an attacker can mount a brute force attack by deciphering the message, or part of it, using each possible shift. The correct description will be

430-514: A right shift of 3. The encryption can also be represented using modular arithmetic by first transforming the letters into numbers, according to the scheme, A → 0, B → 1, ..., Z → 25. Encryption of a letter x by a shift n can be described mathematically as, Decryption is performed similarly, (Here, "mod" refers to the modulo operation . The value x is in the range 0 to 25, but if x + n or x − n are not in this range then 26 should be added or subtracted.) The replacement remains

473-511: 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

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516-408: A special difficulty in the use of codes compared to the secret information used in ciphers , the key , which is typically much shorter. The United States National Security Agency documents sometimes use codebook to refer to block ciphers ; compare their use of combiner-type algorithm to refer to stream ciphers . Codebooks come in two forms, one-part or two-part: The earliest known use of

559-474: 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

602-461: Is a byword for the complete record of a series of codes, regardless of physical format. In cryptography , a codebook is a document used for implementing a code . A codebook contains a lookup table for coding and decoding; each word or phrase has one or more strings which replace it. To decipher messages written in code, corresponding copies of the codebook must be available at either end. The distribution and physical security of codebooks presents

645-405: Is also performed in the ROT13 algorithm , a simple method of obfuscating text widely found on Usenet and used to obscure text (such as joke punchlines and story spoilers ), but not seriously used as a method of encryption. The Vigenère cipher uses a Caesar cipher with a different shift at each position in the text; the value of the shift is defined using a repeating keyword. If the keyword

688-547: Is as long as the message, is chosen at random , never becomes known to anyone else, and is never reused, this is the one-time pad cipher, proven unbreakable. However the problems involved in using a random key as long as the message make the one-time pad difficult to use in practice. Keywords shorter than the message (e.g., " Complete Victory " used by the Confederacy during the American Civil War ), introduce

731-463: Is known as frequency analysis . For example, in the English language the plaintext frequencies of the letters E , T , (usually most frequent), and Q , Z (typically least frequent) are particularly distinctive. Computers can automate this process by assessing the similarity between the observed frequency distribution and the expected distribution. This can be achieved, for instance, through

774-437: 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

817-453: Is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet . For example, with a left shift of 3, D would be replaced by A , E would become B , and so on. The method is named after Julius Caesar , who used it in his private correspondence. The encryption step performed by

860-481: 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

903-468: Is replaced with the letter before it in the Hebrew alphabet the text translates as " YHWH , our God, YHWH", a quotation from the main part of the scroll. In the 19th century, the personal advertisements section in newspapers would sometimes be used to exchange messages encrypted using simple cipher schemes. David Kahn (1967) describes instances of lovers engaging in secret communications enciphered using

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946-413: Is sometimes known as "completing the plain component". Another approach is to match up the frequency distribution of the letters. By graphing the frequencies of letters in the ciphertext, and by knowing the expected distribution of those letters in the original language of the plaintext, a human can easily spot the value of the shift by looking at the displacement of particular features of the graph. This

989-413: Is the plain alphabet rotated left or right by some number of positions. For instance, here is a Caesar cipher using a left rotation of three places, equivalent to a right shift of 23 (the shift parameter is used as the key ): When encrypting, a person looks up each letter of the message in the "plain" line and writes down the corresponding letter in the "cipher" line. Deciphering is done in reverse, with

1032-541: 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

1075-541: The Caesar cipher in The Times . Even as late as 1915, the Caesar cipher was in use: the Russian army employed it as a replacement for more complicated ciphers which had proved to be too difficult for their troops to master; German and Austrian cryptanalysts had little difficulty in decrypting their messages. Caesar ciphers can be found today in children's toys such as secret decoder rings . A Caesar shift of thirteen

1118-471: The Caesar cipher was at the time; there is no record at that time of any techniques for the solution of simple substitution ciphers. The earliest surviving records date to the 9th-century works of Al-Kindi in the Arab world with the discovery of frequency analysis . A piece of text encrypted in a Hebrew version of the Caesar cipher is sometimes found on the back of Jewish mezuzah scrolls. When each letter

1161-463: 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

1204-453: 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

1247-423: 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

1290-450: 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

1333-441: 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

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1376-417: 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 . Codebook A codebook is a type of document used for gathering and storing cryptography codes . Originally, codebooks were often literally books , but today "codebook"

1419-546: 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

1462-450: The non-cryptographic purpose of data compression. Codebooks are used in relation to precoding and beamforming in mobile networks such as 5G and LTE . The usage is standardized by 3GPP , for example in the document TS 38.331 , NR; Radio Resource Control (RRC); Protocol specification. Caesar cipher In cryptography , a Caesar cipher , also known as Caesar's cipher , the shift cipher , Caesar's code , or Caesar shift ,

1505-442: The one which makes sense as English text. An example is shown on the right for the ciphertext " exxegoexsrgi "; the candidate plaintext for shift four " attackatonce " is the only one which makes sense as English text. Another type of brute force attack is to write out the alphabet beneath each letter of the ciphertext, starting at that letter. Again the correct decryption is the one which makes sense as English text. This technique

1548-436: The order of the letters of the alphabet, that not a word could be made out. If anyone wishes to decipher these, and get at their meaning, he must substitute the fourth letter of the alphabet, namely D, for A, and so with the others." His nephew, Augustus , also used the cipher, but with a right shift of one, and it did not wrap around to the beginning of the alphabet: "Whenever he wrote in cipher, he wrote B for A, C for B, and

1591-409: The rest of the letters on the same principle, using AA for Z." Evidence exists that Julius Caesar also used more complicated systems, and one writer, Aulus Gellius , refers to a (now lost) treatise on his ciphers: "There is even a rather ingeniously written treatise by the grammarian Probus concerning the secret meaning of letters in the composition of Caesar's epistles." It is unknown how effective

1634-476: 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

1677-589: The same throughout the message, so the cipher is classed as a type of monoalphabetic substitution , as opposed to polyalphabetic substitution . The Caesar cipher is named after Julius Caesar , who, according to Suetonius , used it with a shift of three (A becoming D when encrypting, and D becoming A when decrypting) to protect messages of military significance. While Caesar's was the first recorded use of this scheme, other substitution ciphers are known to have been used earlier. "If he had anything confidential to say, he wrote it in cipher, that is, by so changing

1720-423: 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

1763-429: The utilization of the chi-squared statistic or by minimizing the sum of squared errors between the observed and known language distributions. The unicity distance for the Caesar cipher is about 2, meaning that on average at least two characters of ciphertext are required to determine the key. In rare cases more text may be needed. For example, the words " river " and " arena " can be converted to each other with

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1806-563: Was convicted in the United Kingdom of "terrorism offences" after using the Caesar cipher to communicate with Bangladeshi Islamic activists discussing plots to blow up British Airways planes or disrupt their IT networks. Although the parties had access to far better encryption techniques (Karim himself used PGP for data storage on computer disks), they chose to use their own scheme (implemented in Microsoft Excel ), rejecting

1849-461: 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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