Understanding SHA1 and the SMS Pet Food Project

[jonny5ive]

This message is mostly for Tony DiCola, but anyone else who is familiar with the SMS pet food project can chime in.

I'm forking that project on GitHub for a different application. My background in C is spotty, but I want to learn by truly embracing this particular project fully, 100%, so that I understand every single line of code, including the SHA1.h and SHA1.cpp files.

Put another way: I am a chemical engineer by undergrad. My goal is to understand this one single code as well as I understand chemical engineering. That might take a while but that's ok.

My code works, but that's not good enough. I need to understand this inside and out.

A few things I am not to clear on:
- Why the use of pointers ("*") in some cases; e.g., the function void snsPublish(const char* topic, const char* message, unsigned long currentTime) ?
- Why is there an need for a .h and a .cpp file for sha1, and how does the Arduino know how to compile both of those correctly?
- What is the deal with sha in general and how can I learn more about that?
- Why convert the signature to base 64?

...things like that. Ideally some kind of reading list, book recommendation, youtube vids, or heck, a rough kind of syllabus, would help me. It's ok to say RTFM -- but what manual?

Thanks Adafruit :)

-Jonny 5ive