Can anyone help me write this code??? 1. Vernam Encryption Write a program in C

Question

Can anyone help me write this code???

1.

Vernam Encryption

Write a program in C that will encrypt a le use XOR and a

Vernam key. A Vernam key is a short string. (The real system used a much longer random

sequence.) Read the input at low level, as binary data (hint unsigned char is useful here.)

Then xor each character in the binary data with the character in the key. When you get

to the end of the key reuse the key from the beginning.

The program should take command line arguments for the key, input and output.

./vern abc input.clear output.encrypted

Note that the cipher should decrypt its own output. The command:

./vern abc output.encrypted input.clear

should recover the original input. If you use open to create the output le, you may want

to also set O

RDWR or O

WRONLY as well as O

CREAT. You could also use fread and

fwrite for this problem.

2.

Finding the period

This cipher is vulnerable if the key repeats, and with a short key, like abc above, it will

repeat many times for any reasonably sized input.

The incidence of coincidence slides the cipher along itself and counts the number of times

the same symbol is seen.

ABCABCABC count is 9

ABCABCABC

then shift 1

ABCABCABC count is 0

ABCABCABC

then shift 2

ABCABCABC count is 0

ABCABCABC

then shift 3

ABCABCABC count is 6

ABCABCABC

Clearly the period is 3.

Write the code to do that. The le classcipher.vrn is in my directory for this.

3.

EXTRA CREDIT

The character ' ' (space) is most common in English text. After

nding the period count the most common character for each period and recover the key

by XOR'ing it with ' '.

Explanation / Answer

ABCABCABC count is 9
ABCABCABC
then shift 1
ABCABCABC count is 0
ABCABCABC
then shift 2
ABCABCABC count is 0
ABCABCABC
then shift 3
ABCABCABC count is 6
ABCABCABC
Clearly the period is 3.

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