Introduction

The Ink Protocol smart contract resides on the Ethereum blockchain [Etherscan] and is open source [GitHub]. It is responsible for and stores both the XNK token as well as all transaction data, including feedback.

Overview

The Ink Protocol Token (XNK)

XNK (pronounced "Ink") is an ERC20 compatible token, and serves as the method of payment for all Ink Protocol transactions. It has a fixed supply (500M tokens) and is divisible to 18 decimals.

Ink Protocol Transactions

An Ink Protocol Transaction represents a transaction between a buyer and seller, and can take many forms:

It can be a physical or digital good, or even a service that is being provided.
It can take place on established online marketplaces like Listia or classifieds like Craigslist and Facebook Marketplace. Any platform can use Ink Protocol, so you could also use it to pay for goods and services in traditional settings like a flea market or perhaps paying a babysitter.

Data stored on the blockchain

Most of the data surrounding a transaction is stored directly on the blockchain via events:

The transaction owner (the marketplace or payment app it was created on)
Buyer and seller Ethereum addresses
The transaction amount (in XNK)
Mediators and mediation/escrow policies
Feedback rating and dispute history

Data stored off-chain

There are two important pieces of information about a transaction that aren't stored directly on the blockchain, but are instead represented by a hash that is stored on-chain:

Metadata about the good or service being sold (descriptions, photos, etc)
The buyer's feedback comment that accompanies the quantitative rating

Next steps:

Get to know the entire flow a transaction can go through
Learn about each type of Event that is emitted by the smart contract
Find out how metadata and feedback are hashed and subsequently fetched

Account Linking

In addition to the XNK token and transaction data, the Ink Protocol smart contract also handles an important feature called Account Linking. As sellers start to use Ink Protocol across multiple marketplaces, account linking allows them to aggregate the reputation they've built into a single profile. Learn more.