EOS Whitepaper - A Blockchain Operating System

EOS Whitepaper - A Blockchain Operating System

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Dan Larimer
The EOS.IO software introduces a new blockchain architecture designed to enable vertical and horizontal scaling of decentralized applications. This is achieved by creating an operating system-like construct upon which applications can be built. The software provides accounts, authentication, databases, asynchronous communication and the scheduling of applications across hundreds of CPU cores or clusters. The resulting technology is a blockchain architecture that scales to millions of transactions per second, eliminates user fees, and allows for quick and easy deployment of decentralized applications.

Consensus Algorithm (DPOS)
EOS.IO software utilizes the only decentralized consensus algorithm capable of meeting the performance requirements of applications on the blockchain. Under this algorithm, those who hold tokens on a blockchain adopting the EOS.IO software may select block producers through a continuous approval voting system and anyone may choose to participate in block production and will be given an opportunity to produce blocks proportional to the total votes they have received relative to all other producers. For private blockchains the management could use the tokens to add and remove IT staff.

The EOS.IO software enables blocks to be produced exactly every 3 seconds and exactly one producer is authorized to produce a block at any given point in time. If the block is not produced at the scheduled time then the block for that time slot is skipped. When one or more blocks are skipped, there is a 6 or more second gap in the blockchain.

Using the EOS.IO software blocks are produced in rounds of 21. At the start of each round 21 unique block producers are chosen. The top 20 by total approval are automatically chosen every round and the last producer is chosen proportional to their number of votes relative to other producers. The selected producers are shuffled using a pseudorandom number derived from the block time. This shuffling is done to ensure that all producers maintain balanced connectivity to all other producers.

If a producer misses a block and has not produced any block within the last 24 hours they are removed from consideration until they notify the blockchain of their intention to start producing blocks again. This ensures the network operates smoothly by minimizing the number of blocks missed by not scheduling those who are proven to be unreliable.

Under normal conditions a DPOS blockchain does not experience any forks because the block producers cooperate to produce blocks rather than compete. In the event there is a fork, consensus will automatically switch to the longest chain. This metric works because the rate at which blocks are added to a blockchain chain fork is directly correlated to the percentage of block producers that share the same consensus. In other words, a blockchain fork with more producers on it will grow in length faster than one with fewer producers. Furthermore, no block producer should be producing blocks on two forks at the same time. If a block producer is caught doing this then such block produce

The EOS.IO software permits all accounts to be referenced by a unique human readable name of 2 to 32 characters in length. The name is chosen by the creator of the account. All accounts must be funded with the minimal account balance at the time they are created to cover the cost of storing account data. Account names also support namespaces such that the owner of account @domain is the only one who can create the account @user.domain.

In a decentralized context, application developers will pay the nominal cost of account creation to sign up a new user. Traditional businesses already spend significant sums of money per customer they acquire in the form of advertising, free services, etc. The cost of funding a new blockchain account should be insignificant in comparison. Fortunately, there is no need to create accounts for users already signed up by another application.

Deterministic Parallel Execution of Applications
Blockchain consensus depends upon deterministic (reproducible) behavior. This means all parallel execution must be free from the use of mutexes or other locking primitives. Without locks there must be some way to guarantee that all accounts can only read and write their own private database. It also means that each account processes messages sequentially and that parallelism will be at the account level.

In an EOS.IO software-based blockchain, it is the job of the block producer to organize message delivery into independent threads so that they can be evaluated in parallel. The state of each account depends only upon the messages delivered to it. The schedule is the output of a block producer and will be deterministically executed, but the process for generating the schedule need not be deterministic. This means that block producers can utilize parallel algorithms to schedule transactions.

Part of parallel execution means that when a script generates a new message it does not get delivered immediately, instead it is scheduled to be delivered in the next cycle. The reason it cannot be delivered immediately is because the receiver may be actively modifying its own state in another thread.

Token Model and Resource Usage
All blockchains are resource constrained and require a system to prevent abuse. With a blockchain that uses EOS.IO software, there are three broad classes of resources that are consumed by applications:
  1. Bandwidth and Log Storage (Disk)
  2. Computation and Computational Backlog (CPU)
  3. State Storage (RAM)
Bandwidth and computation have two components, instantaneous usage and long-term usage. A blockchain maintains a log of all messages and this log is ultimately stored and downloaded by all full nodes. With the log of messages it is possible to reconstruct the state of all applications.

The computational debt is calculations that must be performed to regenerate state from the message log. If the computational debt grows too large then it becomes necessary to take snapshots of the blockchain's state and discard the blockchain's history. If computational debt grows too quickly then it may take 6 months to replay 1 year worth of transactions. It is critical, therefore, that the computational debt be carefully managed.

Blockchain state storage is information that is accessible from application logic. It includes information such as order books and account balances. If the state is never read by the application then it should not be stored. For example, blog post content and comments are not read by application logic so they should not be stored in the blockchain's state. Meanwhile the existence of a post/comment, the number of votes, and other properties do get stored as part of the blockchain's state.

Block producers publish their available capacity for bandwidth, computation, and state. The EOS.IO software allows each account to consume a percentage of the available capacity proportional to the amount of tokens held in a 3-day staking contract. For example, if a blockchain based on the EOS.IO software is launched and if an account holds 1% of the total tokens distributable pursuant to that blockchain, then that account has the potential to utilize 1% of the state storage capacity.

Adopting the EOS.IO software on a launched blockchain means bandwidth and computational capacity are allocated on a fractional reserve basis because they are transient (unused capacity cannot be saved for future use). The algorithm used by EOS.IO software is similar to the algorithm used by Steem to rate-limit bandwidth usage.

Governance is the process by which people reach consensus on subjective matters that cannot be captured entirely by software algorithms. An EOS.IO software-based blockchain implements a governance process that efficiently directs the existing influence of block producers. Absent a defined governance process, prior blockchains relied ad hoc, informal, and often controversial governance processes that result in unpredictable outcomes.

A blockchain based on the EOS.IO software recognizes that power originates with the token holders who delegate that power to the block producers. The block producers are given limited and checked authority to freeze accounts, update defective applications, and propose hard forking changes to the underlying protocol.

Embedded into the EOS.IO software is the election of block producers. Before any change can be made to the blockchain these block producers must approve it. If the block producers refuse to make changes desired by the token holders then they can be voted out. If the block producers make changes without permission of the token holders then all other non-producing full-node validators (exchanges, etc) will reject the change.

Scripts & Virtual Machines
The EOS.IO software will be first and foremost a platform for coordinating the delivery of authenticated messages to accounts. The details of scripting language and virtual machine are implementation specific details that are mostly independent from the design of the EOS.IO technology. Any language or virtual machine that is deterministic and properly sandboxed with sufficient performance can be integrated with the EOS.IO software API.

Inter Blockchain Communication
EOS.IO software is designed to facilitate inter-blockchain communication. This is achieved by making it easy to generate proof of message existence and proof of message sequence. These proofs combined with an application architecture designed around message passing enables the details of inter-blockchain communication and proof validation to be hidden from application developers.

The EOS.IO software is designed from experience with proven concepts and best practices, and represents fundamental advancements in blockchain technology. The software is part of a holistic blueprint for a globally scalable blockchain society in which decentralised applications can be easily deployed and governed.
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