Basic functions used in encryption algorithms
2 What are the two basic functions used in encryption algorithms?
3 How many keys are required for two people to communicate via a symmetric cipher?
4 What is the difference between a block cipher and a stream cipher?
5 What are the two general approaches to attacking a cipher?
6 Why do some block cipher modes of operation only use encryption while others use both encryption and decryption?
7 What is triple encryption?
8 Why is the middle portion of 3DES a decryption rather than an encryption?”
Sample Solution
Basic functions used in encryption algorithms
Substitution and transposition are the two basic functions used in encryption algorithms. In substitution, each and every element in the plain text (letter, bit, group of letters or bits) mapped into different element. In transposition, the elements in the plain text get rearranged. When two people communicate via a symmetric cipher, a single key is used to encrypt and decrypt while communicating. The difference between a block cipher and a stream cipher is that in stream cipher encryption is done on a digital data one bit or one byte at a time using random generated key stream while in block cipher a block of plaintext is treated as one and generates the cipher text of same size using the symmetric key which is provided to both end.