+++
title = "Register"
description = "Register Documentation"
weight = 3
+++

Here you can authenticate yourself with the system.
Only people who are enrolled to the class can open Gradecoin accounts, with some exceptions for people who asked nicely.
This is enforced with your Student ID (e123456) and a one time password you received with your complementary *Welcome to Gradecoin* email.

# Authentication Process
> The cryptographic outputs you are sending over the network are all Base64 Encoded

- Gradecoin's Public Key (`gradecoin_public_key`) is listed on our Moodle page and [here](/gradecoin.pub). Download and load it it to your client.
- Create a JSON object (`P_AR`) with your `metu_id` ("e"+`6 chars`) and `public key` in base64 (PEM) format (`S_PK`) [reference](https://tls.mbed.org/kb/cryptography/asn1-key-structures-in-der-and-pem)
```json
{
    "student_id": "e123456",
    "passwd": "15 char secret",
    "public_key": "---BEGIN PUBLIC KEY..."
}
```

## Cipher Initialization
> Since we are working with AES-128, both key and IV should be 128 bits (or 32 hexadecimal characters)

- Pick a short temporary key (`k_temp`)
- Pick a random IV ([1](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Initialization_vector_(IV))) ([2](https://en.wikipedia.org/wiki/Initialization_vector) (`iv`)).

## Encryption
- Encrypt the serialized string of `P_AR` with 128 bit block [AES](https://en.wikipedia.org/wiki/Initialization_vector) in [CBC](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CBC) mode with [Pkcs7 padding](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Padding) using the temporary key (`k_temp`), the result is `C_AR`. Encode this with base64.
- The temporary key you have picked `k_temp` is encrypted using RSA with [OAEP](https://en.wikipedia.org/wiki/Optimal_asymmetric_encryption_padding) padding scheme using SHA-256 with `gradecoin_public_key`, giving us `key_ciphertext`. Encode this with base64.
- Base64 encode the IV (`iv`) as well.

{% tidbit() %}
The available tools and libraries might warn you about how using the primitives given above are "hazardous". They are, crypto is hard.
{% end %}

- The payload JSON object (`auth_request`) can be serialized now:

```json
{
    "c": "C_AR",
    "iv": "iv",
    "key": "key_ciphertext"
}
```

If your authentication process was valid, you will be given access and your public key fingerprint that is your address.
Please note it down.
You can now sign [JWTs](@/JWT.md) to send authorized transaction requests.
After all this, you might want to bask in the glory of having successfully managing your way through a home-made cryptographic system.
Maybe the Gradecoin you got given as the registration reward will help.

{% tidbit() %}
Seriously, congratulations
{% end %}