InterprocessCommunication-ProcessesAndPipes

Processes and Pipes

The aim of this experiment is to make you familiar with some concepts of processes and interprocess communication and have practical experience on interprocess communication programming using UNIX and POSIX facilities.
You will implement a multi process encryption application that communicates via pipes. The main application will fork next child after it created its two pipelines, on for next child and one for last child. The child processes will communicate with pipes, which are defined before fork() operations. Each process will process the data provided from the previous child process and pass the result to the next child process. In this context, each process will have 2 pipe, one for reading and one for writing.

The main process reads a plain text from the file named plain.txt and a 128-bit key from the file named key.txt. A key must be 128-bit length but plain text may be longer than 128-bit, but it contains exactly fixed-size blocks, e.g. 64 bytes of plain text consists of 8 blocks.
After reading both key and plain data, the main process first writes key file and after 128-bit plain text blocks by dividing plain data to the next-child pipe. Then this process starts to read encrypted blocks from the last child process and writes them to encrypt.txt. All these three files will be in binary format.

The second process applies XOR operation. After reading plain block from main process pipe and applying XOR between the same length plain and key blocks, this process writes the intermediate result to the next child pipe.

The third process applies permutation. In this step, data of length 8 bytes is divided into two blocks as the first 4 and last 4 bytes, and the byte data having the same indices as the two blocks are replaced with each other. For example, the byte at the 0th position replaces the byte at the 4th indent and the 1st byte and the 5th indent. After permutation, the result block is written to next-child pipe.

The fourth process applies substitution. In this step, each byte of the block is replaced with a substitution value which is provided by a substitution-box. This substitution-box will be given in the context of the assignment. After substitution, the result block is written to next-child pipe.

In addition to all this scenario, each process writes to the intermediate results to a file after all data has been processed. The name of this file is in the format “process- .txt”. In this context, you are expected to develop an approach for triggering the writing all blocks received to the file that data blocks sent over the pipe are completed. At the end of this writing process can terminate itself.