This document is an extension of the [Sharding -- Validator](../sharding/validator.md). All behaviors and definitions defined in the Sharding doc carry over unless explicitly noted or overridden.
Becoming a validator in Custody Game is unchanged from Phase 0. See the [Phase 0 validator guide](../../phase0/validator.md#becoming-a-validator) for details.
Beacon chain validator assignments to beacon committees and beacon block proposal are unchanged from Phase 0. See the [Phase 0 validator guide](../../phase0/validator.md#validator-assignments) for details.
Up to `MAX_CUSTODY_SLASHINGS`, [`CustodySlashing`](./beacon-chain.md#custodyslashing) objects can be included in the `block`. The custody slashings must satisfy the verification conditions found in [custody slashings processing](beacon-chain.md#custody-slashings). The validator receives a small "whistleblower" reward for each custody slashing included (THIS IS NOT CURRENTLY THE CASE BUT PROBABLY SHOULD BE).
Up to `MAX_CUSTODY_KEY_REVEALS`, [`CustodyKeyReveal`](./beacon-chain.md#custodykeyreveal) objects can be included in the `block`. The custody key reveals must satisfy the verification conditions found in [custody key reveal processing](beacon-chain.md#custody-key-reveals). The validator receives a small reward for each custody key reveal included.
Up to `MAX_EARLY_DERIVED_SECRET_REVEALS`, [`EarlyDerivedSecretReveal`](./beacon-chain.md#earlyderivedsecretreveal) objects can be included in the `block`. The early derived secret reveals must satisfy the verification conditions found in [early derived secret reveal processing](beacon-chain.md#custody-key-reveals). The validator receives a small "whistleblower" reward for each early derived secret reveal included.
`attestation.data`, `attestation.aggregation_bits`, and `attestation.signature` are unchanged from Phase 0. But safety/validity in signing the message is premised upon calculation of the "custody bit" [TODO].
To avoid custody slashings, the attester must never sign any shard transition for which the custody bit is one. The custody bit is computed using the custody secret:
Note that the valid custody secret is always the one for the **attestation target epoch**, not to be confused with the epoch in which the shard block was generated.
While they are the same most of the time, getting this wrong at custody epoch boundaries would result in a custody slashing.