Introducing the New Validator System

Summary

Kroma introduces a new validator system with a KRO-based incentive structure, improving the current system. This allows $KRO token and Kroma Guardian House (KGH) NFT holders to contribute to network security through delegation, making the Kroma network more secure and robust, while lowering the barrier for non-technical users to participate in the network validation.

Recap of Kroma’s Validator System

On September 5, 2023, with the launch of the Kroma mainnet, we introduced the permissionless validator system. Since the launch, more than 360 accounts have registered as validators, and over 7,500 checkpoint outputs have been submitted by various validators. Through this, Kroma has supported state settlement and withdrawals in a decentralized manner.

Limitations on the Current System

However, the current validator system has the following limitations:

Multiple Accounts on a Single Validator

Since the probability of being selected as a priority validator was not proportional to the amount of ETH deposited, some users exploited this by spreading their ETH across multiple accounts to increase their chances of being selected as priority validators.

Barriers to Participate in the Network

To participate in network validation, users had to deposit ETH and run a validator node, creating a high entry barrier for non-technical users.

To overcome these limitations and enable more users to contribute to enhancing the security of the Kroma network, we have designed a new validator system. This new validator system adopts a KRO-based incentive system, where even non-technical users can contribute to network security and receive $KRO token rewards by delegating $KRO tokens and KGH NFTs.

A New Validator System

Participants

• Validators: Validators become eligible by depositing $KRO tokens on L1. They can submit outputs and validate the outputs submitted by other validators. If a validator detects an invalid output, they can create a challenge. Validators ensure the finalization of valid outputs for the Kroma network, thus protecting assets on the network.
• KRO Delegators: $KRO token holders can delegate their $KRO tokens to validators, increasing the probability of the validator being selected as a priority validator for output submission. Delegators receive a portion of the submission rewards. Delegated $KRO tokens can be undelegated anytime after a 7-day elapsed from delegation.
• KGH Delegators: KGH NFT holders can also delegate the NFTs to validators. Delegating KGH NFTs has the effect of boosting the rewards for output submission, and the delegators receive the rewards. Likewise, delegated KGH NFTs can be undelegated anytime after a 7-day delegation period.

Output Submission

The new validator system retains the priority and public rounds for output submission. Validators are selected as priority validators in proportion to the amount of their delegated $KRO tokens. Only selected priority validators can submit an output during the priority round. If a priority validator does not submit an output within the priority round, the public round opens, allowing any eligible validator to submit an output. Upon submission, a portion of the deposited $KRO tokens is bonded. If the submitted output passes the challenge period and is finalized, the bonded $KRO token is released and the validator receives rewards for output submission. However, if an invalid output is challenged and the validator loses, the bonded $KRO tokens are slashed.

Reward Distribution

Rewards for output submission consist of two parts: base reward and boost reward. The base reward is a fixed amount given for output submission, while the boost reward is additional compensation based on KGH NFT delegation (KGH boosting details ). Validators take a commission from both the base and boost rewards, with the remaining base reward distributed to $KRO token delegators in proportion to the amount of their delegated $KRO tokens. Boost rewards are distributed among KGH NFT delegators based on the amount of delegated KGH NFTs.

Jail

In the new validator system, we have introduced a jail system to disincentivize entities that do not properly fulfill their roles as validators. The roles of validators for Kroma’s security are as below:

• Submitting checkpoint outputs to L1.
• Preventing the finalization of invalid checkpoint outputs through the challenge process.

Validators who fail to perform these critical roles will be jailed and cannot act as validators for a certain period (jail period). Validators who fail to submit outputs in the priority round for a certain number of times are jailed for at least 3 days. Validators who lose in the challenge process are also jailed for at least 7 days. Jailed validators can resume their validator role after the jail period by performing an unjail transaction.

Challenge Process

The new validator system remains compatible with Kroma’s existing ZK fault proof system. If a validator submits an invalid output, an honest validator can challenge it. Similar to output submission, challengers must bond a portion of their deposited $KRO tokens. The winner of a challenge receives a portion of the loser’s bonded $KRO tokens as a reward, with the rest of it paid as a tax to the security council to prevent collusive attacks. The loser of a challenge is also jailed.

Conclusion

Kroma introduces a new validator system that overcomes the limitations of the current validator system of Kroma network and allows $KRO token and KGH NFT holders to contribute to enhancing the security of the Kroma network through delegating their $KRO tokens and KGH NFTs. This will make the Kroma network more secure and strengthen the $KRO token ecosystem. For more details, please refer to the specification document. Upgrade instructions for validators will be provided soon.

About Kroma

As Asia’s leading Layer 2 solution built on the Superchain, Kroma is the first OP Stack rollup with an active fault proof system utilizing zkEVM.
Kroma will transition to a universal ZK Rollup once the generation of ZK proofs becomes more cost-efficient and faster — using its original modular ZK backend library, Tachyon.
Kroma plans to push for gamified web3 experience backed by its strengths in gaming, consumer applications, Asia market, and technical capabilities for true universal web3 adoption.

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