Review Questions Edit

What are the essential ingredients of a symmetric cipher? Edit

  1. Plaintext: The original data that is fed into the algorithm.
  2. Encryption Algorithm: The encryption algorithm performs various substitutions and transformations on the plaintext.
  3. Secret Key: The secret key is also input to the algorithm. 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.
  5. Decryption: This is essentially the encryption algorithm run in inverse. It takes the ciphertext and the same secret key and produces the original plaintext.

What are the two basic functions used in encryption algorithms?  Edit

All encryption algorithms are based on two general principles: Substitution, in which each element in the plaintext is mapped into another element, and transposition, in which elements in the plaintext are rearranged. The fundamental requirement is that no information be lost.


How many keys are required for two people to communicate via a symmetric cipher?  Edit

  Essentially only one key is required, the users will make copies of the key in order to decrypt the text.