+++
title = "Gradecoin"
sort_by = "weight"
+++

# Welcome to Gradecoin!

Blockchains are incredibly simple yet can appear very complicated, we will see how they work and practice programming _production_ cryptography code.

This server is the sandbox for the PA1, it's currently running the Gradecoin application. Gradecoin is the faux currency we will use to simulate a blockchain network. At the end of the simulation, the amount of Gradecoin you hold will be your PA1 grade.

**A quick summary**: authenticate yourself to the system using public key encryption.
Craft [Transaction](@/transaction_docs.md) proposals and tag them using [JWTs](@/JWT.md).
When there are enough transactions then you can propose [Blocks](@/block_docs.md) in the same way.
Blocks need to be _mined_ beforehand using Proof-of-work, or brute force.

Gradecoin offers 3 endpoints at [/register](/register), [/block](/block) and [/transaction](/transaction). You can only send GET requests to /block and /transaction without authorization.
The server is programmed in [RESTful](https://www.service-architecture.com/articles/web-services/representational_state_transfer_rest.html) architecture, there are no `DELETE`, `PUT` or `UPDATE` operations, though.

Gradecoin uses a Proof-of-work block accepting mechanism. It uses single round [Blake2s](https://www.blake2.net/) hashing which produces 256-bit (64 hexadecimal characters) output. The [target](https://wiki.bitcoinsv.io/index.php/Target) hash is _24 bits_ or _6 hexadecimal characters_ of 0. During testing, I could mine a block on average around 4-6 minutes.

> We're expecting you to use existing tools and implementations. Standards are hard. [Don't roll your own crypto](https://www.reddit.com/r/crypto/comments/2coqsy/dont_roll_your_own/). Feel free to ask questions. Collaborate.

You might ask,

> But if nobody has any Gradecoin then how do we have transactions?

There is a bank! Their public key is `31415926535897932384626433832795028841971693993751058209749445923` and they have some amount of Gradecoin preloaded. It's also the only account that you can send transactions requests _to_ yourself.

# Coinbase
The first transactions of a block is called the `coinbase`. They are the **author** of the block proposal and if the block is accepted then they get compensated for their efforts with some Gradecoin.

# Public Key Signatures
Gradecoin uses 2048 bit RSA keyspairs.

# Services
## /register
- Student creates their own 2048 bit RSA `keypair`
- Downloads `Gradecoin`'s Public Key from [Moodle](https://odtuclass.metu.edu.tr/my/)
- Encrypts their JSON wrapped `Public Key`, `Student ID` and one time `passwd` using Gradecoin's Public Key
- Their public key is now in our database and can be used to sign their JWT's during requests

## /transaction
- You can offer a [Transaction](/transaction) - POST request
    - The request should have `Authorization`
    - The request header should be signed by the Public Key of the `by` field in the transaction
- fetch the list of `Transaction`s - GET request

## /block
- offer a [`schema::Block`] - POST request
    - The request should have `Authorization`
    - The [`schema::Block::transaction_list`] of the block should be a subset of [`schema::Db::pending_transactions`]
- fetch the last accepted [`schema::Block`] - GET request

`Authorization`: The request header should have Bearer JWT.Token signed with Student Public Key

# Questions
## This all sound complicated!
- I've drawn inspiration from [actual Bitcoin transactions](https://explorer.bitcoin.com/btc) and [warp](https://github.com/seanmonstar/warp/blob/master/examples/todos.rs). The simplicity of the system is how little interfaces it has.
- Don't know where to start? Gradecoin uses RESTful API; simple `curl` commands or even your browser will work! [This website can help as well](https://curl.trillworks.com/).
- [JWT Debugger](https://jwt.io) and the corresponding [RFC](https://tools.ietf.org/html/rfc7519)
- Remember that you are absolutely encouraged to grab off-the-shelf implementations for every cryptography primitive you will use. You can start by finding a code snippet to generate a RSA keypair?

## I found a bug!
Thank you! Please [let me know](mailto:yigit@ceng.metu.edu.tr) so we can solve it.

## I hacked the server!
That wasn't supposed to happen :( I did not place any intentional vulnerabilities to the system so if you cracked something, it was not intended. Please don't abuse it and let me know so I can patch it.

## Submission?
At the end of the _simulation_, your Gradecoin balance will be your grade. I will also expect a unique client programmed in either;
- c
- c++
- perl
- rust
- python
- random assortment of bash scripts

If your favourite programming language is missing please let me know 🤷?

## Can my friends play?
Sadly, no. Student's who are enrolled to the class will receive one-time-passwords for authentication.

## How and or Why?
- [Built](https://xkcd.com/2314/), [with](https://lofi.cafe/) [Rust](https://xkcd.com/2418/)