Greychain

A complete blockchain in python in little over 1000 lines of code

Dependencies

• python3
• python3-pynacl

What is this

Greychain is a blockchain written by Greyhash AB. Its purpose is to demonstrate blockchain technology.
We would like to hear from you if you are planning on using part of this code in production.

• The blockchain is made up of blocks. Each block has the hash of the previous block, hence it's a chain.
• Each block contains transactions as well as a reward of 13 Greycoins to the miner(creator) of the block.
• Each transaction has:
  • Time
  • Amount
  • Senders public key
  • Receivers public key
  • Comment (For example "Payment for the sheep"
  • Signature

Each transaction is signed by the senders Curve25519 private key.

Greychain run as a node which then becomes a part of the Greychain network. Basically it's a http rest api server communicating using json objects.

How to run

 python3 ./Server.py

To create a transaction, run test_add_transaction.py

python3 ./test/test_add_transactions.py

Operations security

Greyhash focuses heavily on opsec. As such we have provided a systemd service file and a SELinux policy module for Greychain.
To compile and install the SELinux policy is needed.

sudo yum install policycoreutils-devel # Install SELinux dependecies 
make -f /usr/share/selinux/devel/Makefile greychain.pp # Compile the SELinux policy
sudo semodule -i greychain.pp # Load the policy
sudo cp -r ./ /opt/greychain # Install Greychain to /opt/greychain
sudo chown -R nobody /opt/greychain
sudo restorecon -r /opt/greychain/ # Set the correct SELinux filecontexts

The systemd service file assume Greychain is installed under /opt/greychain

sudo cp greychain.service /usr/lib/systemd/system/greychain.service
sudo systemctl daemon-reload
sudo systemctl start greychain.service
sudo systemctl enable greychain.service
sudo systemctl status greychain.service # Show the log