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In Ethereum 2.0 (Sharding Blockchain), a new block requires to be signed by all the validators as members of a committee, where blockchain has been sharded in smaller parts for supporting parallel transaction processing to enhance transaction throughput.

This way, a new block created in a time slot by a proposer, needs to be signed by all the committee's members. All the signatures then will be aggregated using BLS Multi-Signatures With Public-Key Aggregation.

The question is:

What if a malicious validator denies to sign a new block in a shard committee in Ethereum 2.0 ?

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https://ethos.dev/beacon-chain/

Validators are rewarded when they make attestations (LMD GHOST and FFG votes) that the majority of other validators agree with. ...

Validators are penalized for not attesting or if they attest to a block that does not get finalized. ...

If a validator stands to make 10% in a year on rewards, a (honest) validator stands to lose 10% if they do the worst job possible. For example, a validator that is always offline or always votes on blocks that do not get finalized, will be penalized the amount that a validator would be rewarded for making punctual attestations that are finalized.

As long as you don't commit a slashable offense (An LMD GHOST vote is not slashable), the quote above can give you an idea of what you stand to lose.

Slashing is for a different kind of offenses, detailed in the article linked above.

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  • I understand (honest) miners are motivated to attest valid blocks to get more rewards; however, the point is a part of your quot : " Validators are penalized for not attesting ... " Does not it mean that validators are forcing to attest a block?, as otherwise they will be penalized. ** What if an honest validator wants to **forget or ignore that 10% rewards by not signing new blocks?
    – Questioner
    Mar 11, 2020 at 14:44
  • There are micro penalties for this behaviour, you can see them in the phase 0 beacon chain specs: github.com/ethereum/eth2.0-specs/blob/dev/specs/phase0/…
    – Newti
    Mar 11, 2020 at 14:57
  • Additionally, if the chain is not finalizing, there will be quadratic offline penalties to ensure the offline voters will drop out in around 3 weeks (this only happens if a lot of validators don't attest).
    – Newti
    Mar 11, 2020 at 14:59
  • But if penalties for not attesting new block in the committee are micro, cannot it encourage a malicious validator to not signing a block (for censoring that block), as a block in order to be finalized in a shard, requires all validators' signature in a committee. Isn't it?
    – Questioner
    Mar 11, 2020 at 15:13
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    A vote that is made by ⅔ of the total balance of all active validators is valid, so one defector will not change this.
    – Newti
    Mar 11, 2020 at 15:27

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