Incorporation of a variable term into a fixed algorithm, as in this example, is typical of real-world ciphers. Plaintext letter P = ciphertext 62 (alphabet position 16 + 46).Plaintext letter A = ciphertext 47 (alphabet position 1 + 46).Plaintext letter Z = ciphertext 72 (alphabet position 26 + 46).For example, a cipher might be defined by the following rule: "For every letter of plaintext, substitute a two-digit number specifying the plaintext letter's position in the alphabet plus a constant between 1 and 73 that shall be agreed upon in advance." If 46 is the agreed-upon constant, then the plaintext word ZAP enciphers to 724762 as follows: A cipher uses a system of fixed rules (an "algorithm") to transform a legible message ("plaintext") into an apparently random string of characters ("ciphertext"). Such techniques can be used to make encoded messages harder for opponents to read.Ĭiphers. Provides lengthy code phrases for single concepts or nonsense code groups for padding purposes. It can also be made as long as or longer than the original message, if the codebook A coded message may, therefore, be shorter than the original message. Note that a single code group can encode a single word ("king") or an entire phrase ("deliver the films to agent number 3"). Code groups that are words are termed code words and those that are numbers are termed code numbers. "Kill the king at midnight" could thus be encoded, for example, as "OAKEN 7890 SPINDRIFT." Without the code book, it would be difficult for a reader of the encoded message to form an idea of its meaning.Įither a word or a number can be used as a code group. A code is a set of symbolic strings ("code groups") that are listed, along with their assigned meanings, in a code book.Ĭodes encrypt messages by substitution, that is, they substitute code groups for components of the original message. Rather, modern cryptography relies almost entirely on ciphers implemented by digital computers, and is widely employed in industry, diplomacy, espionage, warfare, and personal communications.Ĭodes. Because codes can only communicate concepts that are listed in their codebooks, they have limited flexibility. Codes do so by substituting arbitrary symbols for meanings listed in a codebook ciphers do so by performing rule-directed operations directly on original message text. Both transform legible messages into series of symbols that are intelligible only to specific recipients. Codes and ciphers are forms of cryptography, a term from the Greek kryptos, hidden, and graphia, writing.
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