Terminology of cryptography .....

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  •     Until modern times, cryptography referred almost exclusively to encryption, which is the process of converting ordinary information called plain-text into unintelligible text called cipher-text. 
  •   Decryption is the reverse, in other words, moving from the unintelligible cipher-text back to plain-text. A cipher is a pair of algorithms that create the encryption and the reversing decryption.
  •  The detailed operation of a cipher is controlled both by the algorithm and in each instance by a "key".
  •  The key is a secret (ideally known only to the communicants), usually a short string of characters, which is needed to decrypt the cipher-text.
  •  Formally, a "cryptosystem" is the ordered list of elements of finite possible plain-texts, finite possible cyphertexts, finite possible keys, and the encryption and decryption algorithms which correspond to each key.
  •  Keys are important both formally and in actual practice, as ciphers without variable keys can be trivially broken with only the knowledge of the cipher used and are therefore useless (or even counter-productive) for most purposes.




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