It describes the important concept of blockchains.
[TOC]
| Criteria | Bitcoin | Ethereum | HyperLedger |
|---|---|---|---|
| Opensource? | Yes | Yes | Yes |
| Block time | 10min | 15seconds | Immediately |
| Consensus | PoW | PoW -> PoS | Full-circle verification of the correctness of a set of transactions comprising a block |
| Storage | Transactions | Transactions + code | Transactions |
| Description | Cryptocurrency based on blockchain platform | Generic blockchain platform | Modular blockchain platform |
| Openness | Public | Public | Private + Public |
| Transaction | Transfer of ownership | Message to send by account | Chain Code Execution Message |
Smart contracts are computer protocols that can facilitate, verify or enforce the negotiation or performance of a contract or make a contractual clause unnecessary. They usually have a User Interface and can emulate the logic of contractual clauses. They can execute the terms of a contract in an automated way. They can make contractual clauses partially or fully self-executing and self-enforcing. Smart contracts are implemented using blockchain. Once a smart contract is created, it is placed in a blockchain.
- Smart Contracts eliminate the need of any intermediary like a broker, lawyer etc.
- The documents are encrypted in blockchain, which makes it much more secure. Also, the involved parties can be anonymous and maintain privacy.
- Usually a user has to spend lots of time for paperwork or to manually process documents. Smart contracts can automate the whole process, thereby saving time.
- As smart contracts eliminate the need of intermediaries, it saves costs involved in the whole process.
- As smart contracts are executed in an automated manner, it helps in avoiding errors that result from manual execution.
The use of a consensus algorithm is essential because anyone participating in a block chain can enter, change or delete data. The consensus algorithm can guarantee the reliability of the data stored in the block chain after a specific mechanism operation between authorized users. Thereby blockchain can be safely updated and maintained the state of the block chain, ensuring data integrity within the block chain.
| PoW | PoS | PBFT | |
|---|---|---|---|
| Major Blockchain Platform | Bitcoin, Ethereum | Cardano | Hyperledger fabric 0.6 |
PBFT is an algorithm introduced by Miguel Castro and Barbara Riskop in 1999. It is an algorithm designed for high-speed transaction processing and is capable of handling tens of millions of transactions per second. All participants in the network must be known in advance, and one of the participants will be the Primary. Send a request to all participants. The result for that request is aggregated and the block is committed using multiple values.
- Protocols for synchronizing state machines between multiple replicas
- Even though (N-1) / 3 participants try to fake at the same time, it can withstand.
- A client sends a request to invoke a service operation to the primary (or leader)
- The primary (or leader) multicasts the request to peers
- Each peer executes the request and send a reply to the client
- The client waits for f + 1 replies from different replicas with the same result; This is the result of the operation.
Definitions of each abbreviation in the diagram are;
m: Request message objectc: Client IDt: Timestampv: View IDn: Sequence IDi: Peer(Node) IDr: Result of the request's operation
In this diagram, the fork/join node notation (black thin bars) is used to denote broadcasting the message. Normally, this notation is a control node to support the parallelism in activities.
In the diagram, the peer change its state to prepared or committed when the count value, which is the number of verified messages from other peers, is larger than 2.
Actually, the condition is count >= 2*f where f is the maximum number of faulty peers, which the network can tolerate. In this case, f is just 1, so the condition is count >= 2.
Every node replies the result of the request's operation to the client individually. The client will collect these reply messages and if f + 1 valid reply messages are arrived, the client will accept the result.
The copyright of overall behavior of pbft and the sample implementation of pbft are in bigpicturelabs.
A proof of work(POW) is a piece of data which is difficult (costly, time-consuming) to produce but easy for others to verify and which satisfies certain requirements. Producing a proof of work can be a random process with low probability so that a lot of trial and error is required on average before a valid proof of work is generated.
Let's say the base string that we are going to do work on is "Hello, world!". Our target is to find a variation of it that SHA-256 hashes to a value beginning with '000'. We vary the string by adding an integer value to the end called a nonce and incrementing it each time.
"Hello, world!0" => 1312af178c253f84028d480a6adc1e25e81caa44c749ec81976192e2ec934c64
"Hello, world!1" => e9afc424b79e4f6ab42d99c81156d3a17228d6e1eef4139be78e948a9332a7d8
"Hello, world!2" => ae37343a357a8297591625e7134cbea22f5928be8ca2a32aa475cf05fd4266b7
...
"Hello, world!4248" => 6e110d98b388e77e9c6f042ac6b497cec46660deef75a55ebc7cfdf65cc0b965
"Hello, world!4249" => c004190b822f1669cac8dc37e761cb73652e7832fb814565702245cf26ebb9e6
"Hello, world!4250" => 0000c3af42fc31103f1fdc0151fa747ff87349a4714df7cc52ea464e12dcd4e9
At first, the nodes are mining, without knowing who is the traitor (redundant use). However, in the block where a large number of honest nodes participate, mining is performed first, and transactions used as duplication, which is a traitor, are automatically discarded. When a majority of loyal and honest generals collaborate, the false information naturally disappears.
To make a block, nodes have to solve a very difficult problem. Since a small number of malicious nodes can not solve problems faster and continuously than the majority of nodes involved in mining (because the computing power of many honest nodes is stronger. But if the malicious node's computing power exceeds 51% of the total, it may be vulnerable to security.)
Pros
- Strong security
Cons
- Block creation speed is very slow.
- Use of many resources(Electricity)