本文档中的信息对于PAI币的所有用户都至关重要，请您阅读。

一、概述

PAI区块链将使用SHA-3 / SHAKE-256哈希算法加入到新的PoW / PoS混合共识机制。此硬分叉是强制性的，且不向后兼容，并且之后不会有独立的“分叉前的原始PAI”。

升级到新版本就像使用官方存储库中的2.0.001标签重建paicoind一样简单。参见这里：

https://github.com/projectpai/paicoin/tags

一旦更新了节点，则无需进一步干预。所有现有的RPC / CLI命令和用法将保持不变，尽管将添加一些新命令。

二、目标

根据研究论文《Project PAI 混合共识机制前瞻》提出的建议，Project PAI核心开发人员一直在为下一个PAI区块链迭代开发“混合”工作量证明/权益证明共识机制。此分叉的主要目标是：

1. 删除当前阻止公众自由采矿的白名单机制。白名单最初是为了消除51％的攻击和其他恶意活动而制定的。混合实施的PoS部分将缓解这些漏洞。

2. 摆脱已知为ASIC设备支持的哈希函数，从而减少了进入挖矿的障碍。从理论上讲，这将有助于人们更大程度地参与挖矿。

三、执行

当所有更新的完整节点都切换为使用SHA-3挖矿时，从其本身开始，硬分叉的执行将包括一系列相关事件。以及一个过渡期（ITP）（在此期间逐步启用质押所需的软件组件。） ITP过渡期后删除了挖矿白名单，届时将完全为PAI币启用公共混合PoW / PoS共识。

四、硬分叉

混合共识硬分叉过程的执行计划在主网上的区块高度154,550开始。预期将在大约2020年10月6日太平洋标准时间上午10:30开始（北京时间2020年10月7日凌晨1：30），除非PAI区块链的哈希率发生重大变化。

五、过渡期

在PAI区块链分叉区块高度之后，PAI区块链将进入过渡期（ITP），在此期间，质押（PAI币）所需的软件组件将被增量激活。ITP将按以下步骤进行：

● 主网硬分叉：区块高度 154,550

○ 10月6日UTC大约下午5:30。

○ 在块高度154,550，运行PAI Coin Core v2.0.001的所有完整节点都将切换到混合共识。此时的直接影响是挖矿将切换为使用SHA-3 / SHAKE-256。质押尚未启用，仍将强制执行挖矿白名单。

● 购买在区块高度154,806启用的权益凭证

○ 10月8日UTC大约下午12:10

○ 在初始硬分叉后256个块处的块高度154,806，运行PAI Coin Core v2.0.001的所有完整节点将开始接受包括权益凭证购买交易的块。权益凭单（SV）本身尚无资格对新区块进行投票。

● 权益凭证在区块高度155,574块开始投票

○ 10月15日UTC大约下午2:50

○ 在启用了购买SV后的块高度155,574，即768个块上，所有运行PAI Coin Core v2.0.001的完整节点将开始要求将投票交易包括在新区块中。

● 在区块155,718正式公开挖矿（将删除白名单）

○ 10月16日UTC大约下午2:50

○ 在需要对新区块进行投票之后，在区块高度155,718（即权益凭证开始投票后的144区块处），挖矿白名单将停止执行，并且将接受指定任何币种支付地址的有效区块。这将完成向混合PoW / PoS共识的过渡。

六、准备

准备此硬分叉所需做的工作取决于您使用PAI币的方式。

完整节点

如果您在运行一个完整的节点（如果您是从官方Project PAI GitHub存储库运行paicoind，则将执行此操作），则需要在分叉之前更新PAI Coin软件。如果不这样做，则在分叉后，您的节点将停止正常运行。然而，更新步骤非常简单。

您只需要:

1. 将Paicoin代码库的本地版本更新为标记2.0.001

2. 按照doc / build_unix.md中的说明构建paicoind

完成后，您应该能够通过执行以下命令来验证您使用的版本是否正确：

paicoind –version

您会看到:PAIcoin Core Daemon version v2.0.001-[build]

请注意，此版本未更改paicoind的依赖关系和构建要求。同样，paicoind的所有当前可用的RPC / CLI操作仍然存在，并且完全向后兼容。另外，我们添加了一些新命令。

您可以在此处或者 PAI论坛找到有关如何设置，运行和维护PAI硬币完整节点的详细信息：

https://paiforum.com/t/building-and-maintaining-a-pai-coin-full-node/2138

PAI Up 手机端

您需要在分叉之前更新PAI Up Mobile应用程序才能继续使用。可从https://paiup.com下载适用于Android的最新版本。团队正在研究一种安全、简单的iOS应用分发机制，并将很快宣布。我们强烈建议您在更新PAI Up之前写下您的书面密码（12个单词的短语）。如果更新期间发生问题，这将确保您不会丢失钱包和币。

PAI Up 网页端

无需更改。但是，在分叉执行之前和之后的几个小时内都无法访问PAI Up Web Wallet，直到确认分叉后区块链的稳定性为止。

PAI Coin Pool

无需更改。但是，在分叉执行之前和之后的几个小时内将禁用PAI币池的存款和取款，直到确认分叉后区块链的稳定性为止。暂停存取PAI币的具体时间将在接近硬分叉时公布。

火币全球站和其他交易所

如果您是 Huobi Global 或其他PAI Coin交易所的用户，请您注意关注交易所的最新公告。通常，数字货币交易所会在PAI链分叉执行之前和之后的一段时间内禁用所有对于PAI币的存款和提款请求。

七、总结

我们很高兴我们即将把此版本的PAI上所做的工作公之于众。我们相信，它将为PAI带来长期而富有成果的未来。感谢您一直以来的支持！

Project PAI

Hybrid Consensus Hard Fork

THE INFORMATION IN THIS DOCUMENT IS CRITICAL TO ALL USERS OF PAI COIN. PLEASE READ.

Summary

The Project PAI Blockchain will fork to a new PoW/PoS Hybrid Consensus mechanism using an alternative, SHA-3/SHAKE-256 hashing algorithm. This hard fork is mandatory, non-backwards compatible, and there are no provisions for a separate “Original PAI” to continue.

Updating to the new version is as simple as rebuilding paicoind using the 2.0.001 tag from the official repository. See here:

https://github.com/projectpai/paicoin/tags.

Once your node is updated, no further intervention should be required. All existing RPC/CLI commands and usage will remain the same, though some new commands will have been added.

Goals

Following recommendations set out by the research paper, Prospective Hybrid Consensus for Project PAI, Project PAI Core Developers have been working on a “Hybrid” Proof of Work/Proof of Stake consensus mechanism for the next iteration of the PAI Blockchain. The primary goals of this fork are to:

1. Remove the current whitelist that prevents the public from mining freely. The whitelist was originally implemented to disincentivize 51% attacks and other malicious activity.  These vulnerabilities will be alleviated by the PoS portion of the Hybrid implementation.

2. Move away from hashing functions known to be supported by ASIC devices, thereby reducing the barrier to entry for mining. This will theoretically enable greater participation in mining.

Execution

Execution of the hard fork will consist of a series of dependent events, starting with the hard fork itself, when all updated full nodes switch to using SHA-3 mining; followed by an Interim Transition Period (ITP), during which software components required for staking are incrementally enabled. The ITP concludes with the removal of the mining whitelist, at which point public Hybrid PoW/PoS will be fully enabled for PAI Coin,

Hard Fork

The execution of the Hybrid Consensus hard fork process is scheduled to begin at block height 154,550 on mainnet. Barring significant changes in hash rate, this corresponds to approximately 10:30 AM PDT (5:30 PM UTC) on October 6, 2020.

Interim Transition Period

After the forking block height, the blockchain will enter an Interim Transition Period (ITP) during which software components required for staking will be incrementally activated. The ITP will proceed as follows:

● Mainnet Fork at Block 154,550

○ Approximately 5:30 PM UTC on October 6.

○ At block height 154,550, all full nodes running PAI Coin Core v2.0.001 will switch to Hybrid Consensus. The immediate impact at this point is that mining will switch to using SHA-3/SHAKE-256. Staking will not yet be enabled, the mining whitelist will still be enforced.

● Purchasing of Stake Vouchers Enabled at Block 154,806

○ Approximately 12:10 PM UTC on October 8.

○ At block height 154,806, 256 blocks after the initial hard fork, all full nodes running PAI Coin Core v2.0.001 will begin to accept blocks that include Stake Voucher purchase transactions. The Stake Vouchers (SVs) themselves will not yet be eligible to vote on new blocks.

● Stake Vouchers Begin Voting at Block 155,574

○ Approximately 2:50 PM UTC on October 15.

○ At block height 155,574, 768 blocks after purchasing of SVs is enabled, all full nodes running PAI Coin Core v2.0.001 will begin to require that vote transactions be included in new blocks.

● Mining Becomes Public (Whitelist Removed) at Block 155,718

○ Approximately 2:50 PM UTC on October 16.

○ At block height 155,718, 144 blocks after requiring votes on new blocks, the mining whitelist will stop being enforced, and valid blocks specifying any coinbase payout address will be accepted. This will complete the transition to Hybrid PoW/PoS Consensus.

Preparation

What you need to do in preparation for this Hard Fork depends on how you use PAI Coin.

Full Node

If you run a full node (which you would be doing if you are running paicoind from the official Project PAI GitHub repository), you will need to update your PAI Coin software prior to the fork. If you do not, your node will stop functioning properly after the fork. Fortunately, updating should be straightforward.

You simply need to:

1. Update the local version of your paicoin codebase to tag 2.0.001

2. Build paicoind per the instructions in doc/build_unix.md

Once complete, you should be able to verify you are on the correct version by executing:

paicoind –version

And you should see: PAIcoin Core Daemon version v2.0.001-[build]

Note that the dependencies and build requirements for paicoind have not changed with this release. Likewise, all currently available RPC/CLI operations for paicoind are still present and fully backward compatible. Some new commands have been added.

You can find detailed information on how to set up, run, and maintain a PAI Coin Full Node here:

https://paiforum.com/t/building-and-maintaining-a-pai-coin-full-node/2138

PAI Up Mobile

You will need to update your PAI Up Mobile app prior to the fork in order to continue using it. The newest version for Android will be available for download from https://paiup.com. A safe and straightforward distribution mechanism for iOS is being researched and will be announced soon. We strongly encourage you to write down your paper key (12-word seed phrase) before updating PAI Up. This will ensure you do not lose access to your wallet and coins if something goes wrong during the update.

PAI Up Web

No changes are necessary. However, the PAI Up Web Wallet will be inaccessible for several hours before and after the fork execution until stability of the post-fork blockchain is confirmed.

PAI Coin Pool

No changes are necessary. However, PAI Coin Pool deposits and withdrawals will be disabled for several hours before and after the fork execution until stability of the post-fork blockchain is confirmed. The exact timeframe of the suspension of deposits and withdrawals will be announced closer to the hard fork time.

Huobi Global and other exchanges

If you are a user of Huobi Global, or other platforms that exchange PAI Coin, please pay attention to their latest information. It is conventional that they will disable deposits and withdrawals for a period before and after the fork execution.

Conclusion

We are very excited to finally make the work we have been doing on this version of PAI, public.  We believe that it will position PAI for a long and fruitful future.  Thank you for your continued support in making Project PAI a success!