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抵押

波卡(Polkadot) 使用 NPoS(提名权益证明)机制选择验证人，该机制为了验证人和 提名人两种角色，以实现链安全性的最大化。对网络维护感兴趣的参与者可以负责运行验证人节点。在创世区块中，波卡链将为验证人提供有限位置，位置数量将逐步增加至 1000 以上。

系统鼓励 DOT 持有者作为提名人参与。提名人可以支持最多16个他们相信的验证候选人。

验证人角色是在 BABE 负责生成区块，验证平行链区块和确保最终性。提名人可以根据验证人抵押量而作选择。

The staking system pays out rewards essentially equally to all validators regardless of stake. Having more stake on a validator does not influence the amount of block rewards it receives. However, there is a probabilistic component to reward calculation (discussed below), so rewards may not be exactly equal for all validators in a given era.

Distribution of the rewards are pro-rata to all stakers after the validator payment is deducted. In this way, the network incents the nomination of lower-staked validators to create an equally-staked validator set.

Polkadot 抵押的运作方式

1. 确定身份

In staking, you can be either a nominator or a validator.

As a nominator, you can nominate one or more (up to 16) validator candidates that you trust to help you earn rewards in DOT. You can take a look at the nominator guide to understand what you are required to do when the mainnet launches.

A validator node is required to be responsive 24/7, perform its expected duties in a timely manner, and avoid any slashable behavior. You can follow our Kusama validator guide if you would like to run a validator on Kusama.

2. 提名期

Any potential validators can indicate their intention to be a validator candidate. Their candidacies are made public to all nominators, and a nominator in turn submits a list of any number of candidates that it supports. In the next epoch (lasting several hours), a certain number of validators having the most DOT backing get elected and become active. There are no particular requirements for a DOT holder to become a nominator, though we expect each nominator to carefully track the performance and reputation of validators.

Once the nomination period ends, the NPoS election mechanism takes the nominators and their associated votes as input, and outputs a set of validators of the required size, that maximizes the stake backing of any validator, and that makes the stakes backing validators as evenly distributed as possible. The objectives of this election mechanism are to maximize the security of the network, and achieve fair representation of the nominators. If you want to know more about how NPoS works (e.g. election, running time complexity, etc.), please read here.

3. 抵押奖励分配

To explain how rewards are paid to validators and nominators, we need to consider validator pools, where a validator pool consists of an elected validator together with the nominators backing it. (Note: if a nominator n with stake s backs several elected validators, say k, the NPoS election mechanism will split its stakes into pieces s_1, s_2, …, s_k, so that it backs validator i with stake s_i. In that case, nominator n will be rewarded essentially the same as if there were k nominators in different pools, each backing a single validator i with stake s_i). For each validator pool, we keep a list of nominators with the associated stakes.

The general rule for rewards across validator pools is that two validator pools get paid essentially the same amount of DOT for equal work, i.e. they are NOT paid proportional to the stakes in each pool. There is a probabilistic component to staking rewards in the form of era points and tips but these should average out over time. Within a validator pool, a (configurable) percentage of the reward goes to pay the validator's commission fees and the remainder is paid pro-rata (i.e. proportional to stake) to the nominators and validator. Notice in particular that the validator is rewarded twice: once in commission fees for validating (if their commission rate is above 0%), and once for nominating itself with stake.

To estimate the inflation rate and how many DOT you can get each month as a nominator or validator, you can use this tool as a reference and play around with it by changing some parameters (e.g. how many days you would like to stake with your DOT, provider fees, compound rewards, etc.) to have a better estimate. Even though it may not be entirely accurate since staking participation is changing dynamically, it works well as an indicator.

4. 奖励机制

We highlight two features of this payment scheme. The first is that since validator pools are paid the same regardless of stake level, pools with less stake will generally pay more to nominators per-DOT than pools with more stake. We thus give nominators an economic incentive to gradually shift their preferences to lower staked validators that gain a sufficient amount of reputation. The reason for this is that we want the stake across validator pools to be as evenly distributed as possible, to avoid a concentration of power among a few validators. In the long term, we expect all validator pools to have similar levels of stake, with the stake being higher for higher reputation validators (meaning that a nominator that is willing to risk more by backing a validator with a low reputation will get paid more).

The following example should clarify the above. For simplicity, we have the following assumptions:

• 验证人本身不持有权益。
• They each receive the same number of era points.
• There are no tips for any transactions processed.
• They do NOT charge any commission fees.
• Total reward amount is 100 DOT tokens.
• The current minimum amount of DOT to be a validator is 350 (note that this is not the actual value, which fluctuates, but merely an assumption for purposes of this example; to understand how the actual minimal stake is calculated, see here).

	验证人池 A
提名人 (4)	权益 (600)	所占总权益比	奖励
Jin	100	0.167	16.7
Sam	50	0.083	8.3
Anson	250	0.417	41.7
Bobby	200	0.333	33.3

	验证人池 B
提名人 (4)	权益 (400)	所占总权益比	奖励
Alice	100	0.25	25
Peter	100	0.25	25
John	150	0.375	37.5
Kitty	50	0.125	12.5

Both validator pools A & B have 4 nominators with the total stake 600 and 400 respectively.

Based on the above rewards distribution, nominators in validator pool B get more rewards per DOT than those in pool A because pool A has more overall stake. Sam has staked 50 DOT in pool A, but he only gets 8.3 in return, whereas Kitty gets 12.5 with the same amount of stake.

There is an additional factor to consider in terms of rewards. While there is no limit to the number of nominators a validator may have, a validator does have a limit to how many nominators to which it can pay rewards. In Polkadot and Kusama, this limit is currently 256, although this can be modified via runtime upgrade. A validator with more than 256 nominators is oversubscribed. When payouts occur, only the top 256 nominators as measured by amount of stake allocated to that validator will receive rewards. All other nominators are essentially "wasting" their stake - they used their nomination to elect that validator to the active stake, but receive no rewards in exchange for doing so.

We also remark that when the network slashes a validator slot for a misbehavior (e.g. validator offline, equivocation, etc.) the slashed amount is a fixed percentage (and NOT a fixed amount of DOT), which means that validator pools with more stake get slashed more DOT. Again, this is done to provide nominators with an economic incentive to shift their preferences and back less popular validators whom they consider to be trustworthy.

The second point to note is that each validator candidate is free to name their desired commission fee (as a percentage of rewards) to cover operational costs. Since validator pools are paid the same, pools with lower commission fees pay more to nominators than pools with higher fees. Thus, each validator can choose between increasing their fees to earn more DOT, or decreasing their fees to attract more nominators and increase their chances of being elected. We will let the market regulate itself in this regard. In the long term, we expect that all validators will need to be cost efficient to remain competitive, and that validators with higher reputation will be able to charge slightly higher commission fees (which is fair).

账户

There are two different accounts for managing your funds: Stash and Controller.

• Stash: 这帐户储存资金用作绑定 DOTs 参与抵押，但将某些功能委托给 Controller。因此使用 Controller 可以积极参与，其保存 Stash 密钥在冷钱包中，这意味着它永远保持离线状态。您还可以指定代理帐户，对治理议案进行投票。
• Controller 这帐户是代表 Stash 帐户负责发出有关提名和验证的操作。它用于设置奖励发送到那个帐户和佣金。如果你是验证人，它亦用作设定 session 密钥，并只需要足够的资金来支付交易费用。

We designed this hierarchy of separate key types so that validator operators and nominators can protect themselves much better than in systems with only one key. As a rule, you lose security anytime you use one key for multiple roles, or even if you use keys related by derivation. You should never use any account key for a "hot" session key in particular.

Controller and Stash account keys can be either sr25519 or ed25519. For more on how keys are used in Polkadot and the cryptography behind it see here.

验证人和提名人

Since validator slots will be limited, most of those who wish to stake their DOT and contribute economic security to the network will be nominators. Validators do most of the heavy lifting: they produce new block candidates in BABE, vote and come to consensus in GRANDPA, validate the state transition function of parachains, and possibly some other responsibilities regarding data availability and XCMP. Nominators, on the other hand, do not need to do anything once they have bonded their DOT. The experience of the nominator is similar to "set it and forget it," while the validator will be doing active service for the network by performing the critical operations. For this reason, the validator has certain privileges regarding the payout of the staking mechanism and will be able to declare its own allocation before the share is divided to nominators.

Note: while the experience of a nominator is similar to "set it and forget it", in reality there are many reasons to keep an eye on one's validators and keep optimizing the nominations for best returns and reduced risk. We talk more about this on the How to Nominate page.

Want to stake DOT?

• Nominator Guide - Become a nominator on the Polkadot network.
• Validator Guide - Become a validator on the Polkadot network.

惩罚 (Slashing)

Slashing will happen if a validator misbehaves (e.g. goes offline, attacks the network, or runs modified software) in the network. They and their nominators will get slashed by losing a percentage of their bonded/staked DOT. Any slashed DOT will be added to the Treasury. The rationale for this (rather than burning or distributing them as rewards) is that slashes may then be reverted by the Council by simply paying out from the Treasury. This would be useful in situations such as a faulty runtime causing slashing or forcing validators offline through no fault of their own. In the case of legitimate slashing, it moves tokens away from malicious validators to those building the ecosystem through the normal Treasury process.

Validator pools with larger total stake backing them will get slashed more harshly than less popular ones, so we encourage nominators to shift their nominations to less popular validators to reduce the possible losses.

It is important to realize that slashing only occurs for active validations for a given nominator, and slashes are not mitigated by having other inactive or waiting nominations. They are also not mitigated by the validator operator running separate validators; each validator is considered its own entity for purposes of slashing, just as they are for staking rewards.

As an example, assume BIG_COMPANY has 50 validators that all go offline at the same time, thus causing a 1% unresponsiveness slash to their nominators. In this example, the nominator has nominated five validators, two of which are with BIG_COMPANY (BC_1 and BC_2) and three are with other validators that do not belong to BIG_COMPANY (OV_1, OV_2, and OV_3). In this era, BC_1 is the active validator for this nominator, BC_2 and OV_1 are inactive, and OV_2 and OV_3 are waiting. The nominator will be slashed 1% of bonded stake, since BC_1 is the active validator. The inactive and waiting validators (BC_2 and OV_1 through 3) don't have any effect on this, since they are not actively validating. Any nominator actively nominating BC_2 also receives a 1% slash, but any nominator actively nominating OV_1 is unaffected.

In rare instances, a nominator may be actively nominating several validators in a single era. In this case, the slash is proportionate to the amount staked to that specific validator. For instance, if another nominator had their stake split 50% to BC_1 and 50% to OV_1, they would receive a slash of 0.5% (50% of 1%). If a nominator were actively nominating BC_1 and BC_2, again with 50% of their stake allocated to each, they would still end up with a 1% slash, since a 1% slash is applied to both halves of their stake. Note that you cannot control the percentage of stake you have allocated to each validator or choose who your active validator will be (except in the trivial case of nominating a single validator). Staking allocations are controlled by the Phragmén algorithm.

Once a validator gets slashed, it goes into the state as an "unapplied slash". You can check this via Polkadot-JS Apps. The UI shows it per validator and then all the affected nominators along with the amounts. While unapplied, a governance proposal can be made to reverse it during this period (7 days on Kusama, 28 days on Polkadot). After the grace period, the slashes are applied.

The following levels of offence are defined (for specific slash amounts, see the equations in the section below):

• Level 1: isolated unresponsiveness, i.e. being offline for an entire epoch. No slashing, only chilling.
• Level 2: concurrent unresponsiveness or isolated equivocation. Slashes a very small amount of the stake and chills.
• Level 3: misconducts unlikely to be accidental, but which do not harm the network's security to any large extent. Examples include concurrent equivocation or isolated cases of unjustified voting in GRANDPA. Slashes a moderately small amount of the stake and chills.
• Level 4: misconduct that poses a serious security or monetary risk to the system, or mass collusion. Slashes all or most of the stake behind the validator and chills.

Let's look at these offences in a bit more detail.

Unresponsiveness

For every session, validators will send an "I'm Online" heartbeat to indicate they are online. If a validator produces no blocks during an epoch and fails to send the heartbeat, it will be reported as unresponsive. Depending on the repeated offences and how many other validators were unresponsive or offline during the epoch, slashing may occur.

Here is the formula for calculation:

Let x = offenders, n = total no. validators

min((3 * (x - (n / 10 + 1))) / n, 1) * 0.07

Note that if less than 10% of all validators are offline, no penalty is enacted.

Validators should have a well-architected network infrastructure to ensure the node is running to reduce the risk of being slashed. A high availability setup is desirable, preferably with backup nodes that kick in only once the original node is verifiably offline (to avoid double-signing and being slashed for equivocation - see below), together with proxy nodes to avoid being DDoSed when your validator node's IP address is exposed. A comprehensive guide on secure validator setup is available here.

GRANDPA Equivocation

A validator signs two or more votes in the same round on different chains.

BABE Equivocation

A validator produces two or more blocks on the Relay Chain in the same time slot.

GRANDPA and BABE equivocation slashing penalty is calculated as below:

设 x = 出错节点, n = 验证人总数

Min( (3 * x / n )^2, 1)

Validators may run their nodes on multiple machines to make sure they can still perform validation work in case one of their nodes goes down. It should be noted that if they do not have good coordination to manage signing machines, then equivocation is possible.

If a validator is reported for any one of the offences they will be removed from the validator set (chilled) and they will not be paid while they are out. They will be considered inactive immediately and will lose their nominators. They need to re-issue intent to validate and gather support from nominators.

If you want to know more details about slashing, please look at our research page.

Chilling

Chilling is the act of removing a validator from the active validator set, also disqualifying them from the set of electable candidates in the next NPoS cycle.

This may be voluntary and validator-initiated, e.g. if there is a planned outage in the validator's surroundings or hosting provider, and the validator wants to exit to protect themselves against slashing. When voluntary, chilling will keep the validator active in the current session, but will move them to the inactive set in the next. The validator will not lose their nominators.

When used as part of a punishment, being chilled carries an implied penalty of being un-nominated. It also disables the validator for the remainder of the current era and removes the offending validator from the next election.

Polkadot allows some validators to be disabled, but if the number of disabled validators gets too large, Polkadot will trigger a new validator election to get a full set. Disabled validators will need to resubmit their intention to validate and regarner support from nominators.

For more on chilling, see the How to Chill page on this wiki.

Slashing Across Eras

There are 3 main difficulties to account for with slashing in NPoS:

• 提名人可以提名多个验证人，然后通过其中任何一个将惩罚。
• 在惩罚之前，抵押在各个时代都可以重复使用。 连续提名 E 个时代的 N 币并不意味着您要惩罚 N*E 币 - 您只有 N 币。
• 惩罚可在事实发生后发现。

To balance this, we only slash for the maximum slash a participant can receive in some time period, rather than the sum. This ensures protection from overslashing. Likewise, the time span over which maximum slashes are computed are finite and the validator is chilled with nominations withdrawn after a slashing event, as stated in the previous section. This prevents rage-quit attacks in which, once caught misbehaving, a participant deliberately misbehaves more because their slashing amount is already maxed out.

奖励分配

Note that Kusama runs approximately 4x as fast as Polkadot, except for block production times. Polkadot will also produce blocks at approximately six second intervals.

Rewards are recorded per session (approximately one hour on Kusama and four hours on Polkadot) and calculated per era (approximately six hours on Kusama and twenty-four hours on Polkadot). Thus, rewards will be calculated four times per day on Kusama and once per day on Polkadot.

Rewards are calculated based on era points, which have a probabilistic component. In other words, there may be slight differences in your rewards from era to era, and even amongst validators in the active set at the same time. These variations should cancel out over a long enough timeline. See the page on Validator Payout Guide for more information on how these are calculated.

In order to be paid your staking rewards, someone must claim them for each validator that you nominate. Staking rewards are kept available for 84 eras, which is approximately 84 days on Polkadot and 21 days on Kusama. For more information on why this is so, see the page on simple payouts.

WARNING: If nobody claims your staking rewards by this time, then you will not be able to claim them and some of your staking rewards will be lost.

领取奖励

If you go to the Staking payouts page on Polkadot-JS, you will see a list of all validators that you have nominated in the past 84 eras and for which you have not yet received a payout. Each one has the option to trigger the payout for all unclaimed eras. Note that this will pay everyone who was nominating that validator during those eras, and anyone can call it. Therefore, you may not see anything in this tab, yet still received a payout if somebody (generally, but not necessarily, another nominator or the validator operator) has triggered the payout for that validator for that era.

If you wish to check if you received a payout, you will have to check via a block explorer. See the relevant Support page for details.

奖励分配例子

    PER_ERA * BLOCK_TIME = **Reward Distribution Time**

    3600 * 6 seconds = 21,600 s = 6 hours

    ***These parameters can be changed by proposing a referendum***

Validators can create a cut of the reward that is not shared with the nominators. This cut is a percentage of the block reward, not an absolute value. After the value gets deducted, the remaining portion is based on their staked value and split between the validator and all of the nominators who have voted for this validator.

For example, assume the block reward for a validator is 10 DOT. A validator may specify validator_payment = 50%, in which case the validator would receive 5 DOT. The remaining 5 DOT would then be split between the validator and their nominators based on the proportion of stake each nominator had. Note that validators can put up their own stake, and for this calculation, their stake acts just as if they were another nominator.

Rewards can be directed to the same account (controller), to the stash account (and either increasing the staked value or not increasing the staked value), or to a completely custom account. It is also possible to top-up / withdraw some bonded DOT without having to un-stake everything.

For specific details about validator payouts, please see this guide.

通胀率

DOT is inflationary; there is no maximum number of DOT as in Bitcoin. Inflation is designed to be 10% in the first year, with validator rewards being a function of amount staked and the remainder going to treasury.

Source: Research - Web3 Foundation

• x-axis: Proportion of DOT staked
• y-轴: 通货膨胀, 年度化百分比
• 蓝线: 参与抵押者的通涨奖励
• 绿线: 抵押参与者的收益率

You can determine the inflation rewards by checking the current staking rate at Polkadot-JS. The above chart shows the inflation model of the network. Depending on the staking participation, the distribution of the inflation to validators/nominators versus the treasury will change dynamically to provide incentives to participate (or not participate) in staking. For instance, all of the inflation would go to the validators/nominators if 50% of all KSM / DOT are staked, but any deviation from the 50% - positive or negative - sends the proportional remainder to the treasury and effectively reduces staking rewards.

For those who are interested in knowing more about the design of inflation model for the network, please see here.

为什么参与抵押?

• 当主网上线，每年 10% 通胀率
• 目标抵押为 50％
• ~20% 年回报

为什么不参与抵押?

• 代币解锁在 Kusama 需要7天，而 Polkadot 则是28天。
• 如果发现验证人行为不当，将执行处罚（请参见 #slashing ）。
• 您将想代币用于平行链插槽。

How many validators does Polkadot have?

Polkadot started with 20 open validator positions and has opened more gradually. The top bound on the number of validators has not been determined yet, but should only be limited by the bandwidth strain of the network due to peer-to-peer message passing. The estimate of the number of validators that Polkadot will have at maturity is around 1000. Kusama, Polkadot's canary network, currently has over 500 validator slots, and the plan is also to slowly grow this number to approximately 1000.

资源

• NPoS 在 Polkadot 怎么运作 - Web3 基金会研究员 Alfonso Cevallos 描述 NPoS 在 Polkadot 的博客文章
• 设置安全验证人