To explore the implementation of caesar cipher encoding and decoding programs.

A cipher is defined as “a secret or disguised way of writing; a code”, and (as a verb): to put (a message) into secret writing; encode.

In the realm of secrecy (think elementary school secret agent), obfuscation is key. If we can remove direct accessibility to the message (encode), yet still preserve its intent, it can be transmit to a recipient who has the ability to retrieve the message (decode).

The caesar cipher (or shift cipher) is a relatively simple cipher, where each letter of the alphabet is shifted by a fixed amount, enabling a once legible message to appear unrecognizeable (at least directly).

Further background information can be found here:

• https://en.wikipedia.org/wiki/Caesar_cipher

There are two processes related to a lossless obfuscation of data:

• encoding - taking the readable text and making it obfuscated, according to a set process
• decoding - taking the obfuscated text and making it readable, by reversing the process

You are to implement two programs (or at least a program with two fundamental modes of operation):

• encode program: takes plain text message as input, along with a cipher key, and outputs the encoded (obfuscated) result
  • key should be provided via command-line argument (or, if present, a file in the current directory called 'cipher.key')
• decode program: takes the encoded (obfuscated) message, along with a cipher key, and outputs the decoded (readable, plain text) result
  • key should be provided via command-line argument (or, if present, a file in the current directory called 'cipher.key')

The key should be a signed char, allowing for a cipher shift of -128 to +127 (your shift can be left or right, depending on the sign of the number).

You can implement this as two separate programs, or as one program that behaves fundamentally different depending on how it is named (ie encode-sam0 operates in encode mode, decode-sam0 operates in decode mode).

Your program should accept input from STDIN until the EOF character is encountered.

Via positive command-line key:

lab46:~/src/cprog/sam0$ ./encode-sam0 2
hello
jgnnq
^D
lab46:~/src/cprog/sam0$ 

Via negative command-line key:

lab46:~/src/cprog/sam0$ ./encode-sam0 -3
hello there
ebiil qebob
^D
lab46:~/src/cprog/sam0$ 

To successfully complete this project, the following criteria must be met:

• Code must compile cleanly (no warnings or errors)
• Output must be correct, and resemble the form given in the sample output above.
• Code must be nicely and consistently indented (you may use the indent tool)
• Code must utilize the algorithm presented above
• Code must be commented
  • have a properly filled-out comment banner at the top
  • have at least 20% of your program consist of //-style descriptive comments
• Track/version the source code in a repository
• Submit a copy of your source code to me using the submit tool.

To submit this program to me using the submit tool, run the following command at your lab46 prompt:

$ submit cprog sam0 sam0-encode.c sam0-decode.c
Submitting cprog project "sam0":
    -> sam0-encode.c(OK)
    -> sam0-decode.c(OK)

SUCCESSFULLY SUBMITTED

You should get some sort of confirmation indicating successful submission if all went according to plan. If not, check for typos and or locational mismatches.