## Review Questions Edit

### **What are the essential ingredients of a symmetric cipher?** Edit

- Plaintext: The original data that is fed into the algorithm.
- Encryption Algorithm: The encryption algorithm performs various substitutions and transformations on the plaintext.
- Secret Key: The secret key is also input to the algorithm. The exact substitutions and transformations performed by the algorithm depend on the key.
- 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.
- 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.