Purpose

This Automated Ceaser Cipher is developed in C and Encoding/Decoding with Ceaser Cipher has always been something I wanted to do because it's amazing how it works. I also wanted to show others a C language implementation of this as there aren't that many around to this extent. If you are not familiar with the Ceaser Cipher please check out this link before reading more.

Functionalities and Usage

Different Files

frequency_table.c

The files takes in text that is either encoded or not, from user input ( stdin ) or a filename provided with -F flag as shown below in the images and outputs to command line ( stdout ) and prints the frequency table which is a table of various character counts.

The frequencies are determined by the following common frequencies :

• Total number of letters in the text
• Total number of characters in the text

decode.c

This file computes frequencies with the first file, then uses a for a given shift "guess". This examines all possible shifts ( 0 - 25) and determines a shift which should decode the message.

copyrecords.c

This file will copy records to a new file ( in binary format ), assuming ; we have a file of records in binary mode which is already provided. They are copied decoded, but these operations are varied provided the use of the flags.

Flags

Below are the first subset of flags that may be used with their details.

• Only -F is to be used for 'frequency_table.c'.
• Any of these flags can be implemented in 'decode.c'.
• Any flags other than -F and -O may be used conjunctively

Example : ./decode –stx –F myfile.txt –O decodedfile.txt

Below is the second subset of flags that may be used for copyrecords.c specifically for the binary operations file.

Compilation

Compilation is done through the makefile provided, with the following operations

• make all
• make clean
• ./frequecy_table <flags>
• ./decode <flags>
• ./copyrecords <flags>

File structure

Everything is provided go ahead and try this program. For easiest use drag the test files to the src folder so that they are easily acessible.

• /Src : Has all the source code, headers and makefiles
• /Demo: In depth look at the flags
• /test: Has all the test files

records file is to be used for input in copyrecords.c text files input ( with encoded message ) are to be used in any of the files

Constraints

• Character count includes special characters \n, \0
• Maximum length of a word 45 characters
• File name maimum length of 20 characters
• Anything that is not a letter is untouched in the encoding/decoding sequences
• Records from inputfile are in order