$(1$ point$)$ This question concerns block cipher modes. We will use a simple affine cipher, which can be expressed in $C$ as follows.

char cipher$($unsigned char block, char key$)$

$\{$

return $($key$+11*$block$)\%256$;

$\}$

Note that the block size is $8$ bits, which is one byte $($and one ASCII character$).$ We will work with the fixed key $0$x$08.$

We now encrypt various plaintexts using modes for this cipher. In every case in which the mode requires an IV$,$ the IV will be OxAA. In the case of CTR mode, we use a $($nonce $|$ counter$)$ arrangement in which the nonce is the left $5$ bits of OxAA and the counter is a $3$ bit counter that begins at $0.$ In all of the problems given below, one character is one block. Each character of the plaintext should be regarded as its corresponding ASCII code.

a$)$ Encrypt the plaintext "spider" using $CTR$ mode. Please enter your answer in hex. $($Please do ${?}^{******}$ not ${?}^{******}$ enter an $0x,$ as this has been done.$)$

$0x$

b$)$ Encrypt the plaintext "spelling" using ECB mode.

Please enter your answer in hex.

$0x$

c$)$ Encrypt the plaintext "mealy" using $CFB$ mode.

Please enter your answer in hex.

$0x$

d$)$ Encrypt the plaintext "mottos" using $CBC$ mode.

Please enter your answer in hex.

$0x$

e$)$ Encrypt the plaintext "downward" using OFB mode. Please enter your answer in hex.

$0x$