$(1$ point$)$ This question concerns block cipher padding. Suppose the block cipher has a block size of $15$ bytes. A certain message ends with a partial block which is $10$ bytes. We must reversibly pad out the message to use some block cipher modes, such as CBC $($even if the last block is full$).$

Consider the following padding strategy.

Determine the number of padding bytes required. This is a number $n$ which satisfies $1n15$ and $n+l(P)$ is a multiple of $15,$ where $l(P)$ is the length of the unpadded plaintext. Pad the plaintext by appending $n$ bytes, each with value $n.$

Suppose the final $($possibly partial$)$ block of the message is $"0$x$00010203040506070809"$ in hexadecimal. Write out the complete final block in hexadecimal. Please do not put a leading $0x$ as this has been written already.

$0x$