Author: Gary Mannion

Lecturer: Ian McLoughlin

SHA256 Algorithm in C

You must write a program in the C programming language that calculates the SHA-256 hecksum of an input. The algorithm is specified in the Secure Hash Standard document supplied by the (United States) National Institute of Standards and Technology. The only pre-requisite is that your program performs the lgorithm — you are free to decide what input the algorithm should be performed on. I suggest you allow the user to input some free text or a filename via the command line.

Compiling

For creating this program I used the Google Cloud platform and created an Instance on my machine to create the algorithm.

If you wish to compile and run thus program you must do the following:

• get a clone of this repo to your desired destination
• cd Theory-of-algorithms
• In order to compile this program the GCC compiler must be installed on your device which is why we opted to use an instance on Google Cloud
• Run the command "gcc -o sha256 sha256.c" in the terminal(or CMD) within your project folder.

Running

After compiling your program you can then run it from terminal using the following command:

./sha256 [filename]

For running from this repo we must run the following command:

./sha256 test.txt

Implementation

The algorithm was coded up under the supervision of Ian McLoughlin by following his video tutorials online. Here are the links to these videos:

• Video - Part 1
• Video - Part 2
• Video - Part 3
• Video - Part 4
• Video - Part 5
• Video - Part 6
• What is SHA256?

Demonstration

The image here shows us what our program is outputting. The file is being correctly read and we can see the text from the file. However, the hashing output is incorrect as we are able to check the correct hashing output here

The image below is what our correct hashing output should be.

• Unfortunately I have been unable to convert from little endian to big endian before the deadline of this project. Despite this I will still work on later on in the year to get this working correctly for my own learning and experience.

Additional Features

• Added to the program a feature that will display out on the output screen the contents of the file.
• Error handling implemented when incorrect file is being ran on the algorithm.
• My code is written to tell me what type of endian is being used(big/little)

Research/References

Big v little endian
fgets function
Converting big to little endian
Checking little or big endiam in C
Hash output checker

Conclusion

This project was done under the guidance of video lectures uploaded online by my lecturer Ian Mcloughlin.

Under Ian McLoughlins supervision I have gained some knowledge of the SHA256 algorithm and also regained my knowledge of the C language.

I would also like to thank Ian for giving us the option of using VIM for completing this project as it gave me the chance to understand and learn how to complete a program in VIM. I also added some experience in using the linux commands within my Google Cloud Instance.