Unit $3$ DES and AES

Skills and elements used

Properties of symmetric ciphers, block encryption algorithms

$1)$ Describe the use of diffusion in a cipher.

$2)$ Describe the use of confusion in a cipher.

$3)$ Describe the use of permutation in a cipher.

$4)$ How does $3$DES improve upon DES?

$5)$ Convert the hexadecimal values to binary and decimal:

$08$

$4$B

$$ FF

$$ AC

$6)$ Convert the following binary values to hexadecimal.

$00001001$

$11111111$

$01100111$

$10110001$

$7)$ Solve the following binary shift problems:

$00001001>>2$

$11111111>>4$

$11111111<<4$

$10110001>>5$

$8)$ The following binary values have been permuted by rotating the bits by $4$ positions such that b$7$b$6$b$5$b$4$b$3$b$2$b$1$b$0->$ b$3$b$2$b$1$b$0$b$7$b$6$b$5$b$4.$ Un$-$permute the bits and decode the ASCII word.

$0100010100010100111001000111010011110100$

$9)$ Using the feistel structure below, and the encryption function shown. Fill in the blanks for the encryption and decryption of the data $($remember to reverse the keys for decryption$).$

Block size: $8$ bits

plaintext input: $11011110$

keys: k$0=1000,$ k$1=0011$

f encryption function: f$($key$,$ data$)->($data $+$ key$)$ mod $16$