Consider a simple system with $8-$bit block size. Assume the encryption $($and decryption$)$ to

be a simple XOR of the key with the input. In other words, to encrypt $x$ with $k$ we simply

perform $xo+k$ giving y$.$ Similarly, to decrypt $y,$ we perform $yo+k$ giving $x.$

You are given the following $16-$bit input. $1111000011110000($or F$0$F$0$ in hexadecimal$).$

For CTR assume the stream of bits to be used for counter to be

$110011001100110011001100110011001100($or CCCCCCCCC$)$

The key to be used $($where appropriate$)$ is $10100011($A$3$ in hexadecimal$).$

Answer the following to calculate the encrypted output with CTR$.($use IV$=0101$ for CTR$).$

Express the output as $4$ hexadecimal characters so it is easy to read.

Encrypting $x1$ :

X$1$: C$1$ Key XOR $($IV$|$CTR$1))$ XOR X$1=?$

Encrypting X$2$:

X$2$: C$2$ Key XOR $($IV$|$CTR$2))$ XOR X$2=?$

C$1($in hexadecimal$)=?$

C$2($in hexadecimal$)=?$

Output $($in hexadecimal$)$ is $?$