The Qtum development team has integrated the POS 3.0 consensus mechanism into Bitcoin Core V0.13

Preface: Today, the Qtum development team has integrated the POS 3.0 consensus mechanism into the Bitcoin Core V0.13 version, and released an internal BTC Core version V0.13 that supports POS3.0. This test network is a byproduct of the Qtum project during the development process and is also part of the future Qtum code. Regarding the release of this internal test version, Qtum initiator Shuai Chu said that this work has added some meaningful explorations based on the existing Bitcoin code and ecology.

Illustration of some of Qtum's code base

The slow confirmation speed of the Bitcoin network, which many people have been complaining about, will be greatly solved in the Qtum system. In addition, we have also considered the possibility of the existence of a hybrid POW+POS Bitcoin network. The POS block may greatly reduce the confirmation time of the Bitcoin network, and also achieve the expansion of the Bitcoin network from another perspective.

As for why Sunny King's relatively mature Proof of Stake mechanism was chosen as part of the Qtum consensus mechanism, Shuai Chu said that it was mainly based on the requirements of Qtum as a public chain. In the design of the consensus mechanism of the public chain system: 1. Consider the security and reliability of the code 2. Consider the degree of decentralization of the network 3. The applicability of the industry. Combining these three factors, we chose SunnyKing's POS mechanism as the basis, added the cost of incentives, and applied this consensus mechanism to the existing Bitcoin 13 version of the code.

Most of the existing POS currency codes are still using the very old code base of bitcoin core version 0.8. The Qtum development team has spanned 5 versions of Bitcoin (V0.9 V0.10 V0.11 V0.12 V0.13), and ported from V0.8 to V0.13. In this version of the POS network, we can use all the latest important features of Bitcoin code, such as isolated verification and future lightning networks. In addition, the Qtum team has also improved SunnyKing's POS mechanism and improved the security of the entire POS consensus mechanism. Using safe, reliable, and fully tested code as the backbone code of the Qtum platform will reduce the learning cost of development members, increase the security of the Qtum system, and achieve great compatibility with the existing Bitcoin and Ethereum ecosystems.

Proof of Stake (POS) is a consensus model for digital currencies where the blockchain is secured by using coins to generate blocks, rather than a network of dedicated hardware. The Proof of Work (PoW) consensus model generates blocks by solving complex problems. This problem is made more difficult by the amount of computing power used.

The POS model allows Qtum owners to use their personal devices to secure the blockchain. This means that a laptop or personal computer can be used instead of expensive application-specific integrated circuits (ASICs), field-programmable graphics arrays (FPGAs), or graphics processor units (GPUs).

At the time of writing, there are currently about 2 million terahashes per second being used to mine blocks. Assuming everyone uses the latest ASIC devices, the Antminer S9, 14 Terahash per second, there would be over 140,000 of these devices. Each device uses 1400 watts of power, which currently costs about $1200.00, so the total value of the equipment is $168 million, and the power is 196 million terahashes. At 10 cents per kilowatt-hour, that's about $470,000 per day. Note that electricity costs vary widely, and there are many older (and inefficient) ASIC hardware protecting the Bitcoin blockchain. As long as the cost of electricity is less than the cost of mining and selling Bitcoins, the difficulty will rise incrementally.

The energy cost of securing Qtum's POS blockchain is a fraction of the traditional POW model. Perhaps the cost would be as low as 10,000 watts to be considered secure. This would require about 100 devices to actively use their "network weight" to attack the block. From this comparison we can see that the POS model is environmentally friendly compared to POW.

Qtum is based on Bitcoin Core version 0.13 and plans to incorporate Blackcoin’s POS 3.0 consensus mechanism. This approach is not without challenges, so we will overcome them in the following 8 steps:

1. Research and choose a consensus mechanism

Blackcoin has implemented 3 POS versions since its inception in 2014. Version 2 addressed many potential security issues and blocked network abuse. Version 3 made some updates, the most notable change being the change from 1% annual POS rewards to a static 1.5 BLK (Blackcoin), meaning that only Blackcoin owners who participated in securing the network by keeping their wallets online have a chance to get a block.

After looking at multiple POS statistical patterns, Qtum decided to integrate Blackcoin POS 3.0 into Bitcoin Core 0.12.

2. Implement Blockchain POS 3.0 into Qtum Core

This part requires a closer look at how Blackcoin POS 3.0 will work in its ecosystem. Blackcoin Core's 'ancestor' comes from the Bitcoin Core version of 2013, so if you want it to work on version 0.12, it needs to be translated into code before it can be compiled.

Blackcoin’s POS 3.0 implementation is complex, and there is no clear explanation in the code about which parts are related to other parts. The code will be distributed in multiple files, and the challenge is for Qtum developers to identify the markers for the parts that can be integrated.

Bitcoin and Blackcoin sync blockchains differently; Blackcoin downloads entire blocks, while Bitcoin separates block headers before downloading them, making them faster to use. The port from Blackcoin has been modified to account for implementation into Bitcoin Core 0.12, along with other changes to the way Blackcoin accepts and processes blocks. Blackcoin's "mining" software will also be integrated, allowing Qtum Core users to solve equations required to generate coins.

3. Test Qtum’s POS implementation without nodes

Once the Blackcoin mining software is implemented in Bitcoin Core 0.12, it will be accessed using a daemon program called via RPC. These modifications enable mining on a single computer, the algorithms are checked, and this phase is successful.

4. The first test network

The first testnet was created with 10 nodes, 5 of which were hardcoded into the newly created Qtum Core. The other 5 were compiled and executed on various cloud computing providers. Once the Genesis block was created, the network was instructed to generate new blocks every 64 seconds, and the difficulty was adjusted every 16 minutes. The reward for the POS block used for testing purposes was 5 coins. Each node was funded by pre-mined coins and was set to mine coins as soon as the daemon (virtual CD-ROM) was started.

5. Qtum POS needs fixes

There were some issues during this phase, and a lot of log output that allowed the developers to fix the issues. Some bugs in the nodes caused communication problems, and some nodes were banned and created their own chains. This difficulty was not well resolved, and some wallets had corruption issues.

Once these issues are resolved, the network will be monitored for a few days to ensure stability.

6. Build Qtum Core on multiple platforms

Linux was used for the first testnet simply because it was the easiest environment to build. In order to build an environment suitable for Mac compilation, appropriate changes had to be made. Initially MingW and Msys2 were used, but there were codebase issues. It was finally decided to use MingW and cross-compile on Linux. This allows the working wallet to be compiled and executed on Mac and Windows 64-bit.

7. Integrate Qtum into Bitcoin Core 0.13

The implementation of Blackcoin POS 3.0 on Bitcoin Core 0.12 was successful, but recent changes to Bitcoin wallets during testing set development back and required a re-evaluation. This decision was made to launch Qtum with the best features. Bitcoin Core 0.13 allows wallets to sync faster, without downloading the entire Blockcoin, only the block headers. This should make the user experience for Qtum owners smoother than with the 0.12 version.

There will be some issues encountered during this phase and wallet transactions will create errors in the log files. The Testnet is left running to watch for any errors.

8. Qtum Quality Assurance Testing

Testing a new blockchain takes time, and each block takes about 60 seconds to generate, in order to keep the block running as long as possible. Then multiple test networks were set up, using 130 cloud-based Linux nodes for sessions. Each test network will run 15,000 blocks.

Due to the implementation of Bitcoin Core 0.13, some POS blocks were partially downloaded when trying to sync. This issue will be fixed soon when the code is updated to accommodate POS and POW blocks. Each testnet successfully mined 15,000 blocks without further issues.