State

Signing Info (Liveness)

Every block includes a set of precommits by the validators for the previous block, known as the LastCommitInfo provided by Tendermint. A LastCommitInfo is valid so long as it contains precommits from +2/3 of total voting power.

Proposers are incentivized to include precommits from all validators in the Tendermint LastCommitInfo by receiving additional fees proportional to the difference between the voting power included in the LastCommitInfo and +2/3 (see fee distribution).

type LastCommitInfo struct {
	Round int32
	Votes []VoteInfo
}

Validators are penalized for failing to be included in the LastCommitInfo for some number of blocks by being automatically jailed, potentially slashed, and unbonded.

Information about validator's liveness activity is tracked through ValidatorSigningInfo. It is indexed in the store as follows:

• ValidatorSigningInfo: 0x01 | ConsAddrLen (1 byte) | ConsAddress -> ProtocolBuffer(ValSigningInfo)

• MissedBlocksBitArray: 0x02 | ConsAddrLen (1 byte) | ConsAddress | LittleEndianUint64(signArrayIndex) -> VarInt(didMiss) (varint is a number encoding format)

The first mapping allows us to easily lookup the recent signing info for a validator based on the validator's consensus address.

The second mapping (MissedBlocksBitArray) acts as a bit-array of size SignedBlocksWindow that tells us if the validator missed the block for a given index in the bit-array. The index in the bit-array is given as little endian uint64.

The result is a varint that takes on 0 or 1, where 0 indicates the validator did not miss (did sign) the corresponding block, and 1 indicates they missed the block (did not sign).

Note that the MissedBlocksBitArray is not explicitly initialized up-front. Keys are added as we progress through the first SignedBlocksWindow blocks for a newly bonded validator. The SignedBlocksWindow parameter defines the size (number of blocks) of the sliding window used to track validator liveness.

The information stored for tracking validator liveness is as follows:

// ValidatorSigningInfo defines a validator's signing info for monitoring their
// liveness activity.
message ValidatorSigningInfo {
  option (gogoproto.equal)            = true;
  option (gogoproto.goproto_stringer) = false;

  string address = 1 [(cosmos_proto.scalar) = "cosmos.AddressString"];
  // Height at which validator was first a candidate OR was unjailed
  int64 start_height = 2;
  // Index which is incremented each time the validator was a bonded
  // in a block and may have signed a precommit or not. This in conjunction with the
  // `SignedBlocksWindow` param determines the index in the `MissedBlocksBitArray`.
  int64 index_offset = 3;
  // Timestamp until which the validator is jailed due to liveness downtime.
  google.protobuf.Timestamp jailed_until = 4 [(gogoproto.stdtime) = true, (gogoproto.nullable) = false];
  // Whether or not a validator has been tombstoned (killed out of validator set). It is set
  // once the validator commits an equivocation or for any other configured misbehiavor.
  bool tombstoned = 5;
  // A counter kept to avoid unnecessary array reads.
  // Note that `Sum(MissedBlocksBitArray)` always equals `MissedBlocksCounter`.
  int64 missed_blocks_counter = 6;
}

Params

The slashing module stores it's params in state with the prefix of 0x00, it can be updated with governance or the address with authority.

• Params: 0x00 | ProtocolBuffer(Params)

// Params represents the parameters used for by the slashing module.
message Params {
  int64 signed_blocks_window  = 1;
  bytes min_signed_per_window = 2
      [(gogoproto.customtype) = "github.com/cosmos/cosmos-sdk/types.Dec", (gogoproto.nullable) = false];
  google.protobuf.Duration downtime_jail_duration = 3 [(gogoproto.nullable) = false, (gogoproto.stdduration) = true];
  bytes                    slash_fraction_double_sign = 4
      [(gogoproto.customtype) = "github.com/cosmos/cosmos-sdk/types.Dec", (gogoproto.nullable) = false];
  bytes slash_fraction_downtime = 5
      [(gogoproto.customtype) = "github.com/cosmos/cosmos-sdk/types.Dec", (gogoproto.nullable) = false];
}