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NCoin

NCoin is demonstrational, Proof of Authority blockchain project, written in TypeScript.

Build

Run npm install then tsc to build the project

Launch

To launch the project, write node dist/index.js with following parameters:

parameter description
-d or --data Folder for persisting data of Blockhain
-m or --mining Run mining module
-k or --key Path for private key file, needed only for mining
-p or --port Port of running NCoin Network Node, default port is 1996
--nb Option for running node without connecting to the existing node initially
-r or --rest Port of running NCoin Rest API. If no argument is passed, rest api will not run

If you want to run mining module, you can type

node dist/index --nb -m -k ./keys/B

If you want to run regular node with rest api, you can type

node dist/index -r 1200

Technical Description

NCoin is demonstration blockchain project, it is written in TypeScript.

As a paradigm for development it was choosed to Functional Reactive Programming implemented by RxJS.

NCoin is using Ethereum's account based structure. It is storing in the current state (the balances of eahc address) inside memory. This is preventing double spending by applying each transaction in the block one by one.

In each transaction, nonce is used, which represents how many transactions previously was made by that address. Transactions in transactions pool or in the block are always sorted by nonce.

Block's header is hashed by SHA5 algorithm. Each block is containing hash of previous block as well.

For signing data, Ecliptic Curve cyrptograpphy was choosen. It is utilising famous Secp256k1 curve for signing and verifying data. Before Signing a block or Transaction, it is hased by SHA256 algorithm.

Addresses of accounts are base64 encoded public keys.

Blocks and Transactions are stored in JSON format. Bellow is described the format of Block and Transaction

Block structure

Key Description
header Header of Block
header.previousBlockHash Hash of previous Block, string
header.depth Depth of the block, number
header.type 0 for Genesis, 1 for Regular Block
header.merkleRoot Merkle root of transactions, string
header.payload Additional payload which can be set by miner, string
signature Signature of SHA256 hashed block's header using Secp256k1 private key, string
authorities Represents public keys of miners, used only in Genesis Block, an array of strings
transactions List of transactions included in the block. The first transaction should be coinbase

Transaction Structure

Key Description
data Regular data of Transaction
data.from Address of sender, string
data.to Address of receiver, string
data.type 0 for coinbase, 1 for regular transaction
data.amount Amount of coins sent by from, number
data.payload Additional payload which can be set by from, string
data.nonce Nonce is generated in determined way, number
signature Signature of SHA256 hashed transaction's data using Secp256k1 private key, string

Storage

For persisting the data of blockchain into storage, LevelDB was choosen. All data is stored as valid JSON string. Bellow is list of keys in LevelDB and their description.

Key Description
b-{blockHash} Block with hash equal to blockHash
t-{txHash} Transaction with hash equal to txHash
state-{blockHash} State of balances on the time of block which hash is equal to blockHash
lastBlock last block

Communication between Nodes

As a protocol for transfering the data between nodes, TCP/IP was choosen. Data sent by nodes is encoded by JSON, the line separated JSON structure is used to transport messages.

JSON Schema is used for validating incoming messages (under development). Once a message is received from a node which is not JSON encoded, the connection will be destroyed.

Bellow is table of available messages

Type Description
hello This is sent by a Node to another Node, to establish a contact
address This is sent as a response to hello message with list of addresses which is known by it
inv This is used to inform other nodes, that it have certain blocks or transaction
getblock Node can send it with last hash of the block which it currently have
getdata This is sent by node receive certain block or transaction
tx this message is used to send transaction
block this message is used to send block
ping every minute a ping message is sent. If ping will fail, TCP connection will be closed

Once node is up and running, it is sending hello message to list of known him addresses. Once response is received, it is sending getdata message with last to it know block's hash to everyone, and as an answer it is receivng inv message with list of all next blocks. Then node can request specific block with getdata message, and receive block with block message.

Rest API

Type Description
GET /blocksCount Get currently available block's count
GET /blocks/:hash Fetch block by it's hash
GET /transactions/:hash Fetch transaction by it's hash
GET /:address/nonce Get next nonce for specified address. This is used to compose transaction
POST /transactions Create a new transaction. Transaction should be signed locally

TODO

This is good list of tasks for developers who wants to get more in blockchain development

  • Change communication protocol from TCP/IP sockets, to HTTP
  • Use Google Protobuffers for encoding data to transfer between nodes
  • Add proof of working algorithm in miner module, use SHA5
  • Use Priority Queue or Red Black Tree data structure instead of Sorted Array for transaction pool
  • Create Helper command line tool, for generating private public keys pair, for signing transaction and so on
  • Design a SPV node from scratch
  • Create Electron APP as a wallet for NCoin
  • Create Mobile APP as a wallet for NCoin
  • Create an explorer web app for NCoin
  • Rebuild everything with Go or C++ !!!