yutanagano / vigenere_cipher

A simple C implementation of the Vigenere cipher

Vigenere Cipher, implemented in C

This is a simple C project implementing the Vigenere cipher, a derivative of the Caesar cipher. Where the Caesar cipher uses a single key value to shift all characters in a message, the Vigenere cipher uses a multi-character word as a key, where each letter represents a particular shift value (A=0, B=1, etc.). See the wikipedia page for more details.

Use

The program (the executable will be named vcipher once compiled) will take in a cipher key as a command line option (using -k) and output an accordingly encrypted version of each line of text it sees in the standard input stream.

Note: vcipher will only read up to 100 characters per line in the standard input.

By default, it will run in encryption mode, but by specifying decryption mode (using option -d) it can decrypt messages symmetrically using the same key as well.

$ echo "text" | ./vcipher -k key
> divd

$ echo "divd" | ./vcipher -k key -d
> text

Note: The cipher will preserve letter capitalisation in the output. All non-alphabetic characters will remain untouched by vcipher, but note that in this implementation, the non-alphabetic characters still contribute to the text-key alignment process. See below for an illustration.

$ echo "text text0text" | ./vcipher -k key
> divd robr0xchx

... because the key-text alignment is as below ...

key:    k e y k e y k e y k e y k e
text:   t e x t   t e x t 0 t e x t
-----------------------------------
        d i v d   r o b r 0 x c h x

Building

Make sure that you have gcc and make installed on your system. Clone this repo. Then, inside the root directory of this project, run:

make main

This will compile a binary of this project onto the current directory. The file will be named vcipher.

If you don't have or don't want to use make, you can manually build by compiling and linking the files as listed below.

gcc \
 main/main.c \
 src/process_key/process_key.c \
 src/string_transform/string_transform.c \
 src/caesar_transform_char/caesar_transform_char.c \
 src/get_shift_at_position/get_shift_at_position.c \
 -o vcipher

Testing

To run the unit tests, run:

make test

This will compile a test suite and then run it straight after. If the output says:

Tests finished, no errors found.

the tests are still passing.

Note: The testing suite may output certain lines such as Bad input: keyword contains non-alphabetical character $ while running the test suite, but this is expected.