15 KiB
Data Structures
Here we describe the data structures in the Tendermint blockchain and the rules for validating them.
The Tendermint blockchains consists of a short list of basic data types:
BlockHeaderVersionBlockIDTimeData(for transactions)CommitandVoteEvidenceDataandEvidence
Block
A block consists of a header, transactions, votes (the commit), and a list of evidence of malfeasance (ie. signing conflicting votes).
type Block struct {
Header Header
Txs Data
Evidence EvidenceData
LastCommit Commit
}
Note the LastCommit is the set of signatures of validators that committed the last block.
Header
A block header contains metadata about the block and about the consensus, as well as commitments to the data in the current block, the previous block, and the results returned by the application:
type Header struct {
// basic block info
Version Version
ChainID string
Height int64
Time Time
// prev block info
LastBlockID BlockID
// hashes of block data
LastCommitHash []byte // commit from validators from the last block
DataHash []byte // MerkleRoot of transaction hashes
// hashes from the app output from the prev block
ValidatorsHash []byte // validators for the current block
NextValidatorsHash []byte // validators for the next block
ConsensusHash []byte // consensus params for current block
AppHash []byte // state after txs from the previous block
LastResultsHash []byte // root hash of all results from the txs from the previous block
// consensus info
EvidenceHash []byte // evidence included in the block
ProposerAddress []byte // original proposer of the block
Further details on each of these fields is described below.
Version
type Version struct {
Block uint64
App uint64
}
The Version contains the protocol version for the blockchain and the
application as two uint64 values.
BlockID
The BlockID contains two distinct Merkle roots of the block.
The first, used as the block's main hash, is the MerkleRoot
of all the fields in the header (ie. MerkleRoot(header).
The second, used for secure gossipping of the block during consensus,
is the MerkleRoot of the complete serialized block
cut into parts (ie. MerkleRoot(MakeParts(block))).
The BlockID includes these two hashes, as well as the number of
parts (ie. len(MakeParts(block)))
type BlockID struct {
Hash []byte
PartsHeader PartSetHeader
}
type PartSetHeader struct {
Total int32
Hash []byte
}
See MerkleRoot for details.
Time
Tendermint uses the Google.Protobuf.WellKnownTypes.Timestamp format, which uses two integers, one for Seconds and for Nanoseconds.
Data
Data is just a wrapper for a list of transactions, where transactions are arbitrary byte arrays:
type Data struct {
Txs [][]byte
}
Commit
Commit is a simple wrapper for a list of signatures, with one for each validator. It also contains the relevant BlockID, height and round:
type Commit struct {
Height int64
Round int
BlockID BlockID
Signatures []CommitSig
}
CommitSig
CommitSig represents a signature of a validator, who has voted either for nil,
a particular BlockID or was absent. It's a part of the Commit and can be used
to reconstruct the vote set given the validator set.
type BlockIDFlag byte
const (
// BlockIDFlagAbsent - no vote was received from a validator.
BlockIDFlagAbsent BlockIDFlag = 0x01
// BlockIDFlagCommit - voted for the Commit.BlockID.
BlockIDFlagCommit = 0x02
// BlockIDFlagNil - voted for nil.
BlockIDFlagNil = 0x03
)
type CommitSig struct {
BlockIDFlag BlockIDFlag
ValidatorAddress Address
Timestamp time.Time
Signature []byte
}
NOTE: ValidatorAddress and Timestamp fields may be removed in the future
(see
ADR-25).
Vote
A vote is a signed message from a validator for a particular block. The vote includes information about the validator signing it.
type Vote struct {
Type byte
Height int64
Round int
BlockID BlockID
Timestamp Time
ValidatorAddress []byte
ValidatorIndex int
Signature []byte
}
There are two types of votes:
a prevote has vote.Type == 1 and
a precommit has vote.Type == 2.
Signature
Signatures in Tendermint are raw bytes representing the underlying signature.
See the signature spec for more.
EvidenceData
EvidenceData is a simple wrapper for a list of evidence:
type EvidenceData struct {
Evidence []Evidence
}
Evidence
Evidence in Tendermint is used to indicate breaches in the consensus by a validator. It is implemented as the following interface.
type Evidence interface {
Height() int64 // height of the equivocation
Time() time.Time // time of the equivocation
Address() []byte // address of the equivocating validator
Bytes() []byte // bytes which comprise the evidence
Hash() []byte // hash of the evidence
Verify(chainID string, pubKey crypto.PubKey) error // verify the evidence
Equal(Evidence) bool // check equality of evidence
ValidateBasic() error
String() string
}
All evidence can be encoded and decoded to and from Protobuf with the EvidenceToProto()
and EvidenceFromProto() functions. The Fork Accountability
document provides a good overview for the types of evidence and how they occur. Each evidence uses
the timestamp of the block that the evidence occured at to indicate the age of the evidence.
DuplicateVoteEvidence represents a validator that has voted for two different blocks
in the same round of the same height. Votes are lexicographically sorted on BlockID.
type DuplicateVoteEvidence struct {
VoteA *Vote
VoteB *Vote
Timestamp time.Time
}
AmnesiaEvidence represents a validator that has incorrectly voted for another block in a
different round to the the block that the validator was previously locked on. This form
of evidence is generated differently from the rest. See this
ADR for more information.
type AmnesiaEvidence struct {
*PotentialAmnesiaEvidence
Polc *ProofOfLockChange
}
LunaticValidatorEvidence represents a validator that has signed for an arbitrary application state.
This attack only applies to Light clients.
type LunaticValidatorEvidence struct {
Header *Header
Vote *Vote
InvalidHeaderField string
Timestamp time.Time
}
Validation
Here we describe the validation rules for every element in a block. Blocks which do not satisfy these rules are considered invalid.
We abuse notation by using something that looks like Go, supplemented with English.
A statement such as x == y is an assertion - if it fails, the item is invalid.
We refer to certain globally available objects:
block is the block under consideration,
prevBlock is the block at the previous height,
and state keeps track of the validator set, the consensus parameters
and other results from the application. At the point when block is the block under consideration,
the current version of the state corresponds to the state
after executing transactions from the prevBlock.
Elements of an object are accessed as expected,
ie. block.Header.
See the definition of State.
Header
A Header is valid if its corresponding fields are valid.
Version
block.Version.Block == state.Version.Consensus.Block
block.Version.App == state.Version.Consensus.App
The block version must match consensus version from the state.
ChainID
len(block.ChainID) < 50
ChainID must be less than 50 bytes.
Height
block.Header.Height > 0
block.Header.Height == prevBlock.Header.Height + 1
The height is an incrementing integer. The first block has block.Header.Height == 1.
Time
block.Header.Timestamp >= prevBlock.Header.Timestamp + state.consensusParams.Block.TimeIotaMs
block.Header.Timestamp == MedianTime(block.LastCommit, state.LastValidators)
The block timestamp must be monotonic. It must equal the weighted median of the timestamps of the valid signatures in the block.LastCommit.
Note: the timestamp of a vote must be greater by at least one millisecond than that of the block being voted on.
The timestamp of the first block must be equal to the genesis time (since there's no votes to compute the median).
if block.Header.Height == 1 {
block.Header.Timestamp == genesisTime
}
See the section on BFT time for more details.
LastBlockID
LastBlockID is the previous block's BlockID:
prevBlockParts := MakeParts(prevBlock)
block.Header.LastBlockID == BlockID {
Hash: MerkleRoot(prevBlock.Header),
PartsHeader{
Hash: MerkleRoot(prevBlockParts),
Total: len(prevBlockParts),
},
}
The first block has block.Header.LastBlockID == BlockID{}.
LastCommitHash
block.Header.LastCommitHash == MerkleRoot(block.LastCommit.Signatures)
MerkleRoot of the signatures included in the block. These are the commit signatures of the validators that committed the previous block.
The first block has block.Header.LastCommitHash == []byte{}
DataHash
block.Header.DataHash == MerkleRoot(Hashes(block.Txs.Txs))
MerkleRoot of the hashes of transactions included in the block.
Note the transactions are hashed before being included in the Merkle tree, so the leaves of the Merkle tree are the hashes, not the transactions themselves. This is because transaction hashes are regularly used as identifiers for transactions.
ValidatorsHash
block.ValidatorsHash == MerkleRoot(state.Validators)
MerkleRoot of the current validator set that is committing the block.
This can be used to validate the LastCommit included in the next block.
Note the validators are sorted by their voting power before computing the MerkleRoot.
NextValidatorsHash
block.NextValidatorsHash == MerkleRoot(state.NextValidators)
MerkleRoot of the next validator set that will be the validator set that commits the next block. This is included so that the current validator set gets a chance to sign the next validator sets Merkle root. Note the validators are sorted by their voting power before computing the MerkleRoot.
ConsensusHash
block.ConsensusHash == state.ConsensusParams.Hash()
Hash of the amino-encoding of a subset of the consensus parameters.
AppHash
block.AppHash == state.AppHash
Arbitrary byte array returned by the application after executing and commiting the previous block. It serves as the basis for validating any merkle proofs that comes from the ABCI application and represents the state of the actual application rather than the state of the blockchain itself.
The first block has block.Header.AppHash == []byte{}.
LastResultsHash
block.LastResultsHash == MerkleRoot([]ResponseDeliverTx)
LastResultsHash is the root hash of a Merkle tree built from ResponseDeliverTx responses (Log,Info, Codespace and Events fields are ignored).
The first block has block.Header.ResultsHash == []byte{}.
EvidenceHash
block.EvidenceHash == MerkleRoot(block.Evidence)
MerkleRoot of the evidence of Byzantine behaviour included in this block.
ProposerAddress
block.Header.ProposerAddress in state.Validators
Address of the original proposer of the block. Must be a current validator.
Txs
Arbitrary length array of arbitrary length byte-arrays.
LastCommit
The first height is an exception - it requires the LastCommit to be empty:
if block.Header.Height == 1 {
len(b.LastCommit) == 0
}
Otherwise, we require:
len(block.LastCommit) == len(state.LastValidators)
talliedVotingPower := 0
for i, commitSig := range block.LastCommit.Signatures {
if commitSig.Absent() {
continue
}
vote.BlockID == block.LastBlockID
val := state.LastValidators[i]
vote.Verify(block.ChainID, val.PubKey) == true
talliedVotingPower += val.VotingPower
}
talliedVotingPower > (2/3)*TotalVotingPower(state.LastValidators)
Includes one vote for every current validator. All votes must either be for the previous block, nil or absent. All votes must have a valid signature from the corresponding validator. The sum total of the voting power of the validators that voted must be greater than 2/3 of the total voting power of the complete validator set.
The number of votes in a commit is limited to 10000 (see types.MaxVotesCount).
Vote
A vote is a signed message broadcast in the consensus for a particular block at a particular height and round.
When stored in the blockchain or propagated over the network, votes are encoded in Amino.
For signing, votes are represented via CanonicalVote and also encoded using amino (protobuf compatible) via
Vote.SignBytes which includes the ChainID, and uses a different ordering of
the fields.
We define a method Verify that returns true if the signature verifies against the pubkey for the SignBytes
using the given ChainID:
func (vote *Vote) Verify(chainID string, pubKey crypto.PubKey) error {
if !bytes.Equal(pubKey.Address(), vote.ValidatorAddress) {
return ErrVoteInvalidValidatorAddress
}
if !pubKey.VerifyBytes(vote.SignBytes(chainID), vote.Signature) {
return ErrVoteInvalidSignature
}
return nil
}
where pubKey.Verify performs the appropriate digital signature verification of the pubKey
against the given signature and message bytes.
Execution
Once a block is validated, it can be executed against the state.
The state follows this recursive equation:
state(1) = InitialState
state(h+1) <- Execute(state(h), ABCIApp, block(h))
where InitialState includes the initial consensus parameters and validator set,
and ABCIApp is an ABCI application that can return results and changes to the validator
set (TODO). Execute is defined as:
func Execute(s State, app ABCIApp, block Block) State {
// Fuction ApplyBlock executes block of transactions against the app and returns the new root hash of the app state,
// modifications to the validator set and the changes of the consensus parameters.
AppHash, ValidatorChanges, ConsensusParamChanges := app.ApplyBlock(block)
nextConsensusParams := UpdateConsensusParams(state.ConsensusParams, ConsensusParamChanges)
return State{
LastResults: abciResponses.DeliverTxResults,
AppHash: AppHash,
LastValidators: state.Validators,
Validators: state.NextValidators,
NextValidators: UpdateValidators(state.NextValidators, ValidatorChanges),
ConsensusParams: nextConsensusParams,
Version: {
Consensus: {
AppVersion: nextConsensusParams.Version.AppVersion,
},
},
}
}