(1) The Bit-Flip Cipher A cipher is a message written in secret code. We will implement some very basic ciphers as described below. Consider an original message m[n] made up of n characters that are found in a typical sentence (e.g., alphabetical/numeric characters, spaces, periods, commas etc..). Write a program called cipher1.c that asks the user for an input string m (which is assumed to be 100 characters or less). It should then create a cipher by taking each character of m and flipping the bits. The result is the character that will be used in the cipher. e.g., if m = ABC, then the cipher is: as follows: The code should create output that shows the binary representation of the characters and their ASCII codes and also shows the cipher characters in binary format and their ASCII codes. It should look as follows: Enter the message to encode... ABC 01000001 = 65 10111110 = -66 01000010 = 66 10111101 = -67 01000011 = 67 10111100 = -68 Cipher = "" (2) The Bit-Reverse Cipher Copy your cipher1.c code to a file called cipher2.c and adjust cipher2.c so that it creates a cipher that takes each character of m and reverses the bits to get the cipher character. e.g., if m = ABC, then the cipher is: B as follows: The code should create output that shows the binary representation of the characters and their ASCII codes and also show the cipher characters in binary format and their ASCII codes. It should look as follows: Enter the message to encode... ABC 01000001 = 65 10000010 = -126 01000010 = 66 01000010 = 66 01000011 = 67 11000010 = -62 Cipher = "B" (3) The Nibble-Swap Cipher Copy your cipher2.c code to a file called cipher3.c and adjust cipher3.c so that it creates a cipher that takes each character of m and swaps the low 4 bits with the high 4 bits to get the cipher character. e.g., if m = ABC, then the cipher is: ?$4, where ? is not displayable as follows:

The code should create output that shows the binary representation of the characters and their ASCII codes and also shows the cipher characters in binary format and their ASCII codes. It should look as follows: Enter the message to encode... ABC 01000001 = 65 00010100 = 20 01000010 = 66 00100100 = 36 01000011 = 67 00110100 = 52 Cipher = " " (4) Random Cipher Write a program called cipher.c that makes use of the three ciphers that you just created. Copy over your cipher-making code into this file. Adjust the main program so that it asks for the user message, and then randomly chooses one of the three ciphers and applies it to the message. The program should then output only (and exactly) 100 characters representing the encoded message followed by -1 valued bytes. If, for example, cipher1 is used and ABC is the message, then the program should output followed by 97 bytes which are all -1. It is important that no other output is made to the screen (i.e., no other printf() calls not even for asking for user input) because the next program will require exactly 100 bytes. (5) Deciphering it all Finally, write a program called decipher.c that will take the result of the cipher.c program and attempt to determine what the original message was by applying all three ciphers and seeing which one gives the most likely result. Now, although we cannot be sure which cipher was used, if we make some assumptions that the original text was mostly alphanumeric characters then we can make a decent guess. To approach this problem first read in the characters from the standard input (i.e., getchar()). We will set up our testing so that the output from the cipher program is fed into the decipher program for testing (based on pipes which we will discus later in the course). Once the array of characters has been read in you should try to decipher the message using each cipher and then choose the most likely match. To find the best match you must take each deciphered character and determine if it is an alphanumeric character (i.e., is it an upper or lowercase letter or a digit from 0 to 9 or the space character). You should count the percentage of decoded characters that are alphanumeric. The cipher that has the highest percentage of decoded alphanumeric characters that will be the cipher that we will assume is the correct one and you should display that result. You should display the count for each cipher as well. To test the code, use the following command (which assumes that the cipher and decipher programs are in the current directory): ./cipher | ./decipher Here is what the output should look like: student@COMP2401-F19:~$ ./cipher | ./decipher This is an Encoded Message ! Match = 46.43% Deciphered String = i1i1y]9 YMY11yY{ Match = 96.43% Deciphered String = This is an Encoded Message ! Match = 57.14% Deciphered String = ai@i@hg@*globjb@+jhnj@H Deciphered Message: "This is an Encoded Message !" student@COMP2401-F19:~$ Make sure to test your code thoroughly. ________________________________________________________________________________