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Symmetric cypher model


A symmetric encryption scheme has five ingredients:-
  • Plaintext
  • Encryption algorithm 
  • Secret key
  • Ciphertext
  • Decryption Algorithm

  1. Plaintext: This is the original intangible message or data that is fed into the algorithm as input.
  2. Encryption algorithm: The encryption algorithm performs various substitu- tions and transformations on the plaintext.
  3. Secret key: The secret key is also input to the encryption algorithm. The key is a value independent of the plaintext and of the algorithm. The algorithm will produce a different output depending on the specific key being used at the time. The exact substitutions and transformations performed by the algorithm depend on the key.
  4. Ciphertext: This is the scrambled message produced as output. It depends on the plaintext and the secret key. For a given message, two different keys will produce two different ciphertexts. The ciphertext is an apparently random stream of data and, as it stands, is unintelligible.
  5. Decryption algorithm: This is essentially the encryption algorithm run in reverse. It takes the ciphertext and the secret key and produces the original plaintext.

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