Client-Server File Encryption

A C program for encrypting and decrypting files over a socket connection.

--- ABOUT ---

This program was part of my operating system studies at Oregon State University. I learned how to utilize the linux socket library as well as the one-time-pad encryption method.

For more information on this encryption method, please see the WikiPedia page.

--- SYSTEM REQUIREMENTS ---

The program runs on Linux-based operating systems.

--- COMPILING INSTRUCTIONS ---

Included is a compileall bash script which will compile the 5 programs in this project.

--- FILES ---

While there are 5 executables generated, there are 7 files (excluding headers) for this project in total. Below is a description of each file and its purpose.

keygen.c

This program compiles to create the keygen executable, which generates a key of N randomly- generated characters, where N is an argument supplied on execution. EXAMPLE:
./keygen 20 > key.txt
This command will utilize the keygen program to create a key of 20 characters and write it to a file called key.txt.

otp_encryption.c

This file supplies helper functions to the encryption and decryption clients and servers. The functions are used to encrypt and decrypt plaintext and cyphertext files.

file_transfer.c

This file supplies helper functions to the encryption and decryption clients and servers. The functions are used to send and receive text over a socket connection.

enc_client.c

This program compiles to create the enc_client executable, which sends a plaintext file and key to the encryption server and receives back the encrypted file, which is outputted to stdout. EXAMPLE:
./enc_client plaintext.txt key.txt 5678 > cyphertext.txt
This command will utilize the enc_client program to send a plaintext file and key to the encryption server on port 5678 and redirect the cyptertext results to a file called cyphertext.txt

enc_server.c

This program compiles to create the enc_server executable, which starts an encryption server listening on the specified port number. The server receives plaintext files and a key from the encryption client and sends back the cyphertext. EXAMPLE:
./enc_server 5678
This command will start an encryption server listening on port 5678.

dec_client.c

This program compiles to create the dec_client executable, which works exactly the same as the encryption client, but instead sends cyphertext to a decryption server to be decrypted and returned as plaintext. EXAMPLE:
./dec_client cyphertext.txt key.txt 5678 > plaintext.txt
This command will utilize the dec_client program to send a cyphertext file and key to the decryption server on port 5678 and redirect the plaintext results to a file called plaintext.txt

dec_server.c

This program compiles to create the dec_server executable, which works exactly the same as the encryption client, but instead receives cyphertext files and a key from a decryption client and sends back the decrypted file, which is outputted to stdout. EXAMPLE:
./dec_server 5678
This command will start an decryption server listening on port 5678.

--- NOTES ---

The encryption server cannot be used to connect to a decryption server, and vice versa. An authentication error message will be printed indicating the wrong client/server type was used.