20 Jul CRYPTOGRAPHY.
Cryptography. The science of developing secret codes has interested many people for centuries.
Some of the simplest codes involve replacing a character, or a group of characters, with another
character, or group of characters. To easily decode these messages, the decoder needs the “key”
that shows the replacement characters. For your second project you will write two programs that
do the following:
1. Write a program to implement a simple code that replaces each character by another character
that is a fixed number of positions away in the collating sequence. For example, if each character
is replaced by the character that is two characters to the right, then the letter ‘a’ is replaced by the
letter ‘c’, the letter ‘b’ is replaced by the letter ‘d’, and so on. Your program should be able to
read a text in a file (create your own, name it “message.txt”), and then generate a new file that
contains the coded text using this encryption technique (name it “encryptMessage.txt”). Do not
change the newline characters or the EOF character.
Your program should allow the user to choose the “key” for encryption, i.e. if the user enters 4
then each character is replaced by a character that is 4 characters to the right or if the user enters
-4 then each character is replaced by 4 characters to the left. Use an ASCII character chart to
make sure that you are replacing the characters properly.
Your program should also create a file called “key.txt” that contains the key used to encrypt the
message.
2. Write a program that will decode the encryption scheme in problem 1. Test your program
using the files generated in 1.
What to turn in: For this project you will only need to turn in the code (just like you have done
for home works and project 1) and the text files used/generated for part 1. Your *.c file must be
well documented, i.e. you must include comments throughout the program. The code must
readable i.e. user proper spacing and indentation. I will be testing your programs using the files
you provide as well as my own message file.
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