General Concepts

What is a validator?

BlockX is powered by Tendermint Core, which relies on a set of validators to secure the network. Validators run a full node and participate in consensus by broadcasting votes which contain cryptographic signatures signed by their private key. Validators commit new blocks in the blockchain and receive revenue in exchange for their work. They also participate in on-procotol treasury governance by voting on governance proposals. A validator's voting influence is weighted according to their total stake.

What is staking?

BlockX is a public Proof-of-Stake (PoS) blockchain, meaning that validator's weight is determined by the amount of staking tokens (BCX) bonded as collateral. These staking tokens can be staked directly by the validator or delegated to them by BCX holders.

Any user in the system can declare its intention to become a validator by sending a create-validator transaction. From there, they become validators.

The weight (i.e. total stake or voting power) of a validator determines whether or not it is an active validator, and also how frequently this node will have to propose a block and how much revenue it will obtain. Initially, only the top 100 validators with the most weight will be active validators. If validators double-sign, or are frequently offline, they risk their staked tokens (including BCX delegated by users) being "slashed" by the protocol to penalize negligence and misbehavior.

What is a full node?

A full node is a program that fully validates transactions and blocks of a blockchain. It is distinct from a light client node that only processes block headers and a small subset of transactions. Running a full node requires more resources than a light client but is necessary in order to be a validator. In practice, running a full-node only implies running a non-compromised and up-to-date version of the software with low network latency and without downtime.

Of course, it is possible and encouraged for any user to run full nodes even if they do not plan to be validators.

What is a delegator?

Delegators are BCX holders who cannot, or do not want to run validator operations themselves. Users can delegate BCX to a validator and obtain a part of its revenue in exchange.

Because they share revenue with their validators, delegators also share responsibility. Should a validator misbehave, each of its delegators will be partially slashed in proportion to their stake. This is why delegators should perform due-diligence on validators before delegating, as well as diversifying by spreading their stake over multiple validators.

Delegators play a critical role in the system, as they are responsible for choosing validators. Be aware that being a delegator is not a passive role. Delegators are obligated to remain vigilant and actively monitor the actions of their validators, switching should they fail to act responsibly.

Becoming a Validator

How to become a validator?

Any participant in the network can signal their intent to become a validator by creating a validator and registering its validator profile. To do so, the candidate broadcasts a create-validator transaction, in which they must submit the following information:

  • Validator's PubKey: Validator operators can have different accounts for validating and holding liquid funds. The PubKey submitted must be associated with the private key with which the validator intends to sign prevotes and precommits.

  • Validator's Address: This is the address used to identify your validator publicly. The private key associated with this address is used to bond, unbond, and claim rewards.

  • Validator's name (also known as the moniker)

  • Validator's website (optional)

  • Validator's description (optional)

  • Initial commission rate: The commission rate on block provisions, block rewards and fees charged to delegators.

  • Maximum commission: The maximum commission rate which this validator will be allowed to charge.

  • Commission change rate: The maximum daily increase of the validator commission.

  • Minimum self-bond amount: Minimum amount of BCX the validator needs to have bonded at all times. If the validator's self-bonded stake falls below this limit, its entire staking pool will be unbonded.

  • Initial self-bond amount: Initial amount of BCX the validator wants to self-bond.

blockxd tx staking create-validator
    --pubkey blockxvalconspub1zcjduepqs5s0vddx5m65h5ntjzwd0x8g3245rgrytpds4ds7vdtlwx06mcesmnkzly
    --amount "100000000000000000000000abcx"
    --from tmp
    --min-self-delegation "1"
    --moniker "validator"
    --chain-id "blockx_12345-1"
    --gas auto
    --node tcp://

Never create your mainnet validator keys using a test keying backend. Doing so might result in a loss of funds by making your funds remotely accessible via the eth_sendTransaction JSON-RPC endpoint.

Ref: Security Advisory: Insecurely configured geth can make funds remotely accessible

Once a validator is created and registered, BCX holders can delegate BCX to it, effectively adding stake to its pool. The total stake of a validator is the sum of the BCX self-bonded by the validator's operator and the BCX bonded by external delegators.

Only the top 100 validators with the most stake are considered the active validators, becoming bonded validators. If ever a validator's total stake dips below the top 100, the validator loses its validator privileges (meaning that it won't generate rewards) and no longer serves as part of the active set (i.e doesn't participate in consensus), entering unbonding mode and eventually becomes unbonded.

Validator keys and states

What are the different types of keys?

In short, there are two types of keys:

  • Tendermint Key: This is a unique key used to sign block hashes. It is associated with a public key blockxvalconspub.

    • Generated when the node is created with blockxd init.

    • Get this value with blockxd tendermint show-validator

  • Application keys: These keys are created from the application and used to sign transactions. As a validator, you will probably use one key to sign staking-related transactions, and another key to sign oracle-related transactions.

What are the different states a validator can be in?

After a validator is created with a create-validator transaction, it can be in three states:

  • bonded: Validator is in the active set and participates in consensus. Validator is earning rewards and can be slashed for misbehavior.

  • unbonding: Validator is not in the active set and does not participate in consensus. Validator is not earning rewards, but can still be slashed for misbehaviour. This is a transition state from bonded to unbonded. If validator does not send a rebond transaction while in unbonding mode, it will take three weeks for the state transition to complete.

  • unbonded: Validator is not in the active set, and therefore not signing blocks. Unbonded validators cannot be slashed, but do not earn any rewards from their operation. It is still possible to delegate BCX to this validator. Un-delegating from an unbonded validator is immediate.

Delegators have the same state as their validator.

Delegations are not necessarily bonded. BCX can be delegated and bonded, delegated and unbonding, delegated and unbonded, or liquid.

What is "self-bond"? How can I increase my "self-bond"?

The validator operator's "self-bond" refers to the amount of BCX stake delegated to itself. You can increase your self-bond by delegating more BCX to your validator account.

Is there a testnet faucet?

If you want to obtain coins for the testnet, you can do so by using the faucet.

Is there a minimum amount of BCX that must be staked to be an active (bonded) validator?

There is no minimum. The top 100 validators with the highest total stake (where total stake = self-bonded stake + delegators stake) are the active validators.

How will delegators choose their validators?

Delegators are free to choose validators according to their own subjective criteria. That said, criteria anticipated to be important include:

  • Amount of self-bonded BCX: Number of BCX a validator self-bonded to its staking pool. A validator with higher amount of self-bonded BCX has more skin in the game, making it more liable for its actions.

  • Amount of delegated BCX: Total number of BCX delegated to a validator. A high stake shows that the community trusts this validator, but it also means that this validator is a bigger target for hackers. Validators are expected to become less and less attractive as their amount of delegated BCX grows. Bigger validators also increase the centralization of the network.

  • Commission rate: Commission applied on revenue by validators before it is distributed to their delegators

  • Track record: Delegators will likely look at the track record of the validators they plan to delegate to. This includes seniority, past votes on proposals, historical average uptime and how often the node was compromised.

Apart from these criteria, there will be a possibility for validators to signal a website address to complete their resume. Validators will need to build reputation one way or another to attract delegators. For example, it would be a good practice for validators to have their setup audited by third parties. Note though, that the BlockX team will not approve or conduct any audit itself.


Do validators need to be publicly identified?

No, they do not. Each delegator will value validators based on their own criteria. Validators will be able(and are advised) to register a website address when they nominate themselves so that they can advertise their operation as they see fit. Some delegators may prefer a website that clearly displays the team running the validator and their resume, while others might prefer anonymous validators with positive track records. Most likely both identified and anonymous validators will coexist in the validator set.

What are the responsiblities of a validator?

Validators have three main responsibilities:

  • Be able to constantly run a correct version of the software: validators need to make sure that their servers are always online and their private keys are not compromised.

  • Provide oversight and feedback on correct deployment of community pool funds: the BlockX protocol includes the a governance system for proposals to the facilitate adoption of its currencies. Validators are expected to hold budget executors to account to provide transparency and efficient use of funds.

Additionally, validators are expected to be active members of the community. They should always be up-to-date with the current state of the ecosystem so that they can easily adapt to any change.

What does staking imply?

Staking BCX can be thought of as a safety deposit on validation activities. When a validator or a delegator wants to retrieve part or all of their deposit, they send an unbonding transaction. Then, BCX undergo a three weeks unbonding period during which they are liable to being slashed for potential misbehaviors committed by the validator before the unbonding process started.

Validators, and by association delegators, receive block provisions, block rewards, and fee rewards. If a validator misbehaves, a certain portion of its total stake is slashed (the severity of the penalty depends on the type of misbehavior). This means that every user that bonded BCX to this validator gets penalized in proportion to its stake. Delegators are therefore incentivized to delegate to validators that they anticipate will function safely.

Can a validator run away with its delegators' BCX?

By delegating to a validator, a user delegates staking power. The more staking power a validator has, the more weight it has in the consensus and processes. This does not mean that the validator has custody of its delegators' BCX. By no means can a validator run away with its delegator's funds.

Even though delegated funds cannot be stolen by their validators, delegators are still liable if their validators misbehave. In such case, each delegators' stake will be partially slashed in proportion to their relative stake.

How often will a validator be chosen to propose the next block? Does it go up with the quantity of BCX staked?

The validator that is selected to mine the next block is called the proposer, the "leader" in the consensus for the round. Each proposer is selected deterministically, and the frequency of being chosen is equal to the relative total stake (where total stake = self-bonded stake + delegators stake) of the validator. For example, if the total bonded stake across all validators is 100 BCX, and a validator's total stake is 10 BCX, then this validator will be chosen 10% of the time as the proposer.

To understand more about the proposer selection process in Tendermint BFT consensus, read more in their official docs.


What is the incentive to stake?

Each member of a validator's staking pool earns different types of revenue:

  • Block rewards: Native tokens of applications run by validators are inflated to produce block provisions. These provisions exist to incentivize BCX holders to bond their stake, as non-bonded BCX will be diluted over time.

  • Transaction fees: BlockX maintains a whitelist of token that are accepted as fee payment. The initial fee token is the bcx.

This total revenue is divided among validators' staking pools according to each validator's weight. Then, within each validator's staking pool the revenue is divided among delegators in proportion to each delegator's stake. A commission on delegators' revenue is applied by the validator before it is distributed.

What is the incentive to run a validator ?

Validators earn proportionally more revenue than their delegators because of commissions.

Validators also play a major role in governance. If a delegator does not vote, they inherit the vote from their validator. This gives validators a major responsibility in the ecosystem.

What is a validator's commission?

Revenue received by a validator's pool is split between the validator and its delegators. The validator can apply a commission on the part of the revenue that goes to its delegators. This commission is set as a percentage. Each validator is free to set its initial commission, maximum daily commission change rate and maximum commission. BlockX enforces the parameter that each validator sets. These parameters can only be defined when initially declaring candidacy, and may only be constrained further after being declared.

How are block provisions distributed?

Block provisions (rewards) are distributed proportionally to all validators relative to their total stake (voting power). This means that even though each validator gains BCX with each provision, all validators will still maintain equal weight.

Let us take an example where we have 10 validators with equal staking power and a commission rate of 1%. Let us also assume that the provision for a block is 1000 BCX and that each validator has 20% of self-bonded BCX.

These tokens do not go directly to the proposer. Instead, they are evenly spread among validators. So now each validator's pool has 100 BCX. These 100 BCX will be distributed according to each participant's stake:

  • Commission: 100*80%*1% = 0.8 BCX

  • Validator gets: 100\*20% + Commission = 20.8 BCX

  • All delegators get: 100\*80% - Commission = 79.2 BCX

Then, each delegator can claim its part of the 79.2 BCX in proportion to their stake in the validator's staking pool. Note that the validator's commission is not applied on block provisions. Note that block rewards (paid in BCX) are distributed according to the same mechanism.

How are fees distributed?

Fees are similarly distributed with the exception that the block proposer can get a bonus on the fees of the block it proposes if it includes more than the strict minimum of required pre-commits.

When a validator is selected to propose the next block, it must include at least ⅔ pre-commits for the previous block in the form of validator signatures. However, there is an incentive to include more than ⅔ precommits in the form of a bonus.

The bonus is linear: it ranges from 1% if the proposer includes ⅔rd pre-commits (minimum for the block to be valid) to 5% if the proposer includes 100% pre-commits. Of course the proposer should not wait too long or other validators may timeout and move on to the next proposer.

As such, validators have to find a balance between wait-time to get the most signatures and risk of losing out on proposing the next block. This mechanism aims to incentivize non-empty block proposals, better networking between validators as well as to mitigate censorship.

Let's take a concrete example to illustrate the aforementioned concept. In this example, there are 10 validators with equal stake. Each of them applies a 1% commission and has 20% of self-bonded BCX. Now comes a successful block that collects a total of 1005 BCX in fees. Let's assume that the proposer included 100% of the signatures in its block. It thus obtains the full bonus of 5%.

We have to solve this simple equation to find the reward RRR for each validator:

9R+R+5%(R)=1005⇔R=1005/10.05=1009R ~ + ~ R ~ + ~ 5\%(R) ~ = ~ 1005 ~ \Leftrightarrow ~ R ~ = ~ 1005 ~/ ~10.05 ~ = ~ 100 9R+R+5%(R)=1005⇔R=1005/10.05=100

  • For the proposer validator:

    • The pool obtains R+5%(R)R ~ + ~ 5\%(R)R+5%(R): 105 BCX

    • Commission: 105∗80%∗1%105 ~ *~ 80\% ~* ~ 1\%105∗80%∗1% = 0.84 BCX

    • Validator's reward: 105∗20%+Commission105 ~ * ~ 20\% ~ + ~ Commission105∗20%+Commission = 21.84 BCX

    • Delegators' rewards: 105∗80%−Commission105 ~ * ~ 80\% ~ - ~ Commission105∗80%−Commission = 83.16 BCX (each delegator will be able to claim its portion of these rewards in proportion to their stake)

    • The pool obtains RRR: 100 BCX

    • Commission: 100∗80%∗1%100 ~ *~ 80\% ~* ~ 1\%100∗80%∗1% = 0.8 BCX

    • Validator's reward: 100∗20%+Commission100 ~ * ~ 20\% ~ + ~ Commission100∗20%+Commission = 20.8 BCX

    • Delegators' rewards: 100∗80%−Commission100 ~ * ~ 80\% ~ - ~ Commission100∗80%−Commission = 79.2 BCX (each delegator will be able to claim its portion of these rewards in proportion to their stake)

What are the slashing conditions?

If a validator misbehaves, its bonded stake along with its delegators' stake and will be slashed. The severity of the punishment depends on the type of fault. There are 3 main faults that can result in slashing of funds for a validator and its delegators:

  • Double-signing: If someone reports on chain A that a validator signed two blocks at the same height on chain A and chain B, and if chain A and chain B share a common ancestor, then this validator will get slashed on chain A.

  • Downtime: If a validator misses more than 95% of the last 10000 blocks, they will get slashed by 0.01%.

  • Unavailability: If a validator's signature has not been included in the last X blocks, the validator will get slashed by a marginal amount proportional to X. If X is above a certain limit Y, then the validator will get unbonded.

Note that even if a validator does not intentionally misbehave, it can still be slashed if its node crashes, looses connectivity, gets DDoS'd, or if its private key is compromised.

Do validators need to self-bond BCX

No, they do not. A validators total stake is equal to the sum of its own self-bonded stake and of its delegated stake. This means that a validator can compensate its low amount of self-bonded stake by attracting more delegators. This is why reputation is very important for validators.

Even though there is no obligation for validators to self-bond BCX, delegators should want their validator to have self-bonded BCX in their staking pool. In other words, validators should have skin-in-the-game.

In order for delegators to have some guarantee about how much skin-in-the-game their validator has, the latter can signal a minimum amount of self-bonded BCX. If a validator's self-bond goes below the limit that it predefined, this validator and all of its delegators will unbond.

How to prevent concentration of stake in the hands of a few top validators?

For now the community is expected to behave in a smart and self-preserving way. When a mining pool in Bitcoin gets too much mining power the community usually stops contributing to that pool. BlockX will rely on the same effect initially. In the future, other mechanisms will be deployed to smoothen this process as much as possible:

  • Penalty-free re-delegation: This is to allow delegators to easily switch from one validator to another, in order to reduce validator stickiness.

  • UI warning: Wallets can implement warnings that will be displayed to users if they want to delegate to a validator that already has a significant amount of staking power.

Technical Requirements

What are hardware requirements?

Validators should expect to provision one or more data center locations with redundant power, networking, firewalls, HSMs and servers.

We expect that a modest level of hardware specifications will be needed initially and that they might rise as network use increases. Participating in the testnet is the best way to learn more.

What are software requirements?

In addition to running an BlockX node, validators should develop monitoring, alerting and management solutions.

What are bandwidth requirements?

BlockX has the capacity for very high throughput compared to chains like Ethereum or Bitcoin.

As such, we recommend that the data center nodes only connect to trusted full nodes in the cloud or other validators that know each other socially. This relieves the data center node from the burden of mitigating denial-of-service attacks.

Ultimately, as the network becomes more used, one can realistically expect daily bandwidth on the order of several gigabytes.

What does running a validator imply in terms of logistics?

A successful validator operation will require the efforts of multiple highly skilled individuals and continuous operational attention. This will be considerably more involved than running a bitcoin miner for instance.

How to handle key management?

Validators should expect to run an HSM that supports ed25519 keys. Here are potential options:

The BlockX team does not recommend one solution above the other. The community is encouraged to bolster the effort to improve HSMs and the security of key management.

What can validators expect in terms of operations?

Running effective operation is the key to avoiding unexpectedly unbonding or being slashed. This includes being able to respond to attacks, outages, as well as to maintain security and isolation in your data center.

What are the maintenance requirements?

Validators should expect to perform regular software updates to accommodate upgrades and bug fixes. There will inevitably be issues with the network early in its bootstrapping phase that will require substantial vigilance.

How can validators protect themselves from Denial-of-Service attacks?

Denial-of-service attacks occur when an attacker sends a flood of internet traffic to an IP address to prevent the server at the IP address from connecting to the internet.

An attacker scans the network, tries to learn the IP address of various validator nodes and disconnect them from communication by flooding them with traffic.

One recommended way to mitigate these risks is for validators to carefully structure their network topology in a so-called sentry node architecture.

Validator nodes should only connect to full-nodes they trust because they operate them themselves or are run by other validators they know socially. A validator node will typically run in a data center. Most data centers provide direct links the networks of major cloud providers.

The validator can use those links to connect to sentry nodes in the cloud. This shifts the burden of denial-of-service from the validator's node directly to its sentry nodes, and may require new sentry nodes be spun up or activated to mitigate attacks on existing ones.

Sentry nodes can be quickly spun up or change their IP addresses. Because the links to the sentry nodes are in private IP space, an internet based attacked cannot disturb them directly. This will ensure validator block proposals and votes always make it to the rest of the network.

It is expected that good operating procedures on that part of validators will completely mitigate these threats.

For more on sentry node architecture, see this.

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