SHA256-le

A simple implementation of the SHA256 hashing algorithm in C

By: Jane Hacker - janehacker.com

Disclaimer

I did this for fun and experimentation. It is clearly NOT consumer, user, or probably even superuser friendly. You will only find it useful as a developer, and then only if you are really interested in the inner workings of SHA265 and just want a simple step by step example of the process that you can build, trace though, and play with in actually code.

DO NOT USE THIS CODE IN PRODUCTION, don't even use it in your projects unless it really helps to have a skeleton implementation.

There are production ready implementations of SHA256 from multiple sources in probably every language imaginable, use these in your code!

This code is in no way guaranteed to work.
There are very few, if any checks.
No way it is near the fastest.
It is not tested for portability, do so at your own risk! (And read notes below, they might help)

There are sure to be bugs...
...and poor general coding practices
...and poor C coding practices
...and overflows
...and underflows
...and every other kind of flow possible

What is it good for

Learning SHA256 and maybe hashing in general (it is simple)
Having an SHA256 implementation to play with (and in C)
It prints out each compression step's hash output
I have found this to be VERY useful in checking and debugging other/your own SHA256 implementations or other related code
There is commented code to print various steps of the initialization process in binary

What is included

The source... Yup.
This README
A super simple Makefile
A Windows binary
Which probably requires MinGW or Cygwin libraries
And might be for 64-bit systems only

What is wrong not so good with it

Endianness
I have it swap the input so it works on x86 and other little-endian architectures
because I used big-endian constants, I don't know why
If using this code on a big-endian system just skipping the swap step should work... maybe
Uses ROR instruction by default
Which is common on x86
Not on, say... ARM
There is a commented macro without it though
Honestly the non-ROR version is probably faster in the end?
It uses C99 standard
Which makes playing with it, coding, and readability easier
I'm sure works with newer versions
But requires a C99 compatable compiler, or a few rewrites for ones without it
I doubt even the newest of C programmers would have any trouble doing those rewrites...
Requires an entire extra argument on the command line to compile (--std=c99 if you didn't know, and couldn't look in the Makefile)

Credits

Pseudo-code

From Wikipedia's entry for "SHA-2"
http://en.wikipedia.org/wiki/SHA-2#Pseudocode
In history if for some reason it is (re)moved or changed:
http://en.wikipedia.org/w/index.php?title=SHA-2&diff=630108357&oldid=17306306#Pseudocode

Binary printer (function named "p")

Is from an answer on stack overflow
http://stackoverflow.com/a/3974138

Data-ptr/SHA256-le