In some cases the terms codes and ciphers are also used synonymously to substitution and transposition. Some systems used both codes and ciphers in one system, using superencipherment to increase the security. ex "The quick brown fox jumps over the lazy dog" becomes "The quick brown 狐 jumps 上 the lazy 犬".Ĭiphers, 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. Codes work at the level of meaning-that is, words or phrases are converted into something else and this chunking generally shortens the message.Īn 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.Īnother 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 Japanese utilize Kanji (meaning Chinese characters in Japanese) characters to supplement their language. Within technical discussions, however, the words "code" and "cipher" refer to two different concepts. In non-technical usage, a "(secret) code" typically means a "cipher". If one key cannot be deduced from the other, the asymmetric key algorithm has the public/private key property and one of the keys may be made public without loss of confidentiality. If the algorithm is an asymmetric one, the enciphering key is different from, but closely related to, the deciphering key. If the algorithm is symmetric, the key must be known to the recipient and sender and to no one else. By whether the same key is used for both encryption and decryption ( symmetric key algorithms), or if a different key is used for each ( asymmetric key algorithms).By whether they work on blocks of symbols usually of a fixed size ( block ciphers), or on a continuous stream of symbols ( stream ciphers).Most modern ciphers can be categorized in several ways Without knowledge of the key, it should be extremely difficult, if not impossible, to decrypt the resulting ciphertext into readable plaintext. A key must be selected before using a cipher to encrypt a message. The encrypting procedure is varied depending on the key, which changes the detailed operation of the algorithm. The operation of a cipher usually depends on a piece of auxiliary information, called a key (or, in traditional NSA parlance, a cryptovariable). The ciphertext message contains all 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. 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. There are exceptions and some cipher systems may use slightly more, or fewer, characters when output versus the number that were input.Ĭodes operated by substituting according to a large codebook which linked a random string of characters or numbers to a word or phrase. 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.Ĭodes generally substitute different length strings of character in the output, while ciphers generally substitute the same number of characters as are input. To encipher or encode is to convert information into cipher or code. An alternative, less common term is encipherment. 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. Also includes runically unrelated blackletter writing style and pigpen cipher. Edward Larsson's rune cipher resembling that found on the Kensington Runestone.
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