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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.
A cipher uses a system of fixed rules (an "algorithm") to transform a legible message ("plaintext") into an apparently random string of characters ("ciphertext"). 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:
Plaintext letter Z = ciphertext 72 (alphabet position 26 + 46).
Plaintext letter A = ciphertext 47 (alphabet position 1 + 46).
Plaintext letter P = ciphertext 62 (alphabet position 16 + 46).
Incorporation of a variable term into a fixed algorithm, as in this example, is typical of real-world ciphers.
ariable component is termed a key. A real key would be longer and would have a more complex relationship to the cipher algorithm than the key in this example, but its basic role would be the same: a key fits into an algorithm so as to enable enciphering and deciphering, just as a physical key fits into a lock to enable locking and unlocking. Without a key, a cipher algorithm is missing an essential part. In fact, so important is the concept of the key that in real-world ciphering it is not algorithms that are kept secret, but keys. Cipher designers assume that their algorithms will always become known to their opponents, but design the relationship between key and algorithm so that even knowing the algorithm it is almost impossible to decipher a ciphertext without knowing the appropriate key. Before a cipher can work, therefore, a key or set of keys must be in the possession of both the sender and the receiver.
If the key were always the same, it would simply constitute a permanent part of the algorithm, and keying would have no special advantage over trying to keep one's algorithm secret to begin with.Keys must, therefore, be changed occasionally. A new key may be employed every day, for every message, or on some other schedule.
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Author notes:hi po bwahahah vote and comment po kayo para makapag update ako ng mga codes and ciphers.
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