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- # Overview
-
- This is a markdown specification of the Tendermint blockchain.
- It defines the base data structures, how they are validated,
- and how they are communicated over the network.
-
- If you find discrepancies between the spec and the code that
- do not have an associated issue or pull request on github,
- please submit them to our [bug bounty](https://tendermint.com/security)!
-
- ## Contents
-
- - [Overview](#overview)
-
- ### Data Structures
-
- - [Encoding and Digests](https://github.com/tendermint/tendermint/blob/master/docs/spec/blockchain/encoding.md)
- - [Blockchain](https://github.com/tendermint/tendermint/blob/master/docs/spec/blockchain/blockchain.md)
- - [State](https://github.com/tendermint/tendermint/blob/master/docs/spec/blockchain/state.md)
-
- ### Consensus Protocol
-
- - [Consensus Algorithm](/docs/spec/consensus/consensus.md)
- - [Creating a proposal](/docs/spec/consensus/creating-proposal.md)
- - [Time](/docs/spec/consensus/bft-time.md)
- - [Light-Client](/docs/spec/consensus/light-client.md)
-
- ### P2P and Network Protocols
-
- - [The Base P2P Layer](https://github.com/tendermint/tendermint/tree/master/docs/spec/p2p): multiplex the protocols ("reactors") on authenticated and encrypted TCP connections
- - [Peer Exchange (PEX)](https://github.com/tendermint/tendermint/tree/master/docs/spec/reactors/pex): gossip known peer addresses so peers can find each other
- - [Block Sync](https://github.com/tendermint/tendermint/tree/master/docs/spec/reactors/block_sync): gossip blocks so peers can catch up quickly
- - [Consensus](https://github.com/tendermint/tendermint/tree/master/docs/spec/reactors/consensus): gossip votes and block parts so new blocks can be committed
- - [Mempool](https://github.com/tendermint/tendermint/tree/master/docs/spec/reactors/mempool): gossip transactions so they get included in blocks
- - Evidence: Forthcoming, see [this issue](https://github.com/tendermint/tendermint/issues/2329).
-
- ### Software
-
- - [ABCI](/docs/spec/software/abci.md): Details about interactions between the
- application and consensus engine over ABCI
- - [Write-Ahead Log](/docs/spec/software/wal.md): Details about how the consensus
- engine preserves data and recovers from crash failures
-
- ## Overview
-
- Tendermint provides Byzantine Fault Tolerant State Machine Replication using
- hash-linked batches of transactions. Such transaction batches are called "blocks".
- Hence, Tendermint defines a "blockchain".
-
- Each block in Tendermint has a unique index - its Height.
- Height's in the blockchain are monotonic.
- Each block is committed by a known set of weighted Validators.
- Membership and weighting within this validator set may change over time.
- Tendermint guarantees the safety and liveness of the blockchain
- so long as less than 1/3 of the total weight of the Validator set
- is malicious or faulty.
-
- A commit in Tendermint is a set of signed messages from more than 2/3 of
- the total weight of the current Validator set. Validators take turns proposing
- blocks and voting on them. Once enough votes are received, the block is considered
- committed. These votes are included in the _next_ block as proof that the previous block
- was committed - they cannot be included in the current block, as that block has already been
- created.
-
- Once a block is committed, it can be executed against an application.
- The application returns results for each of the transactions in the block.
- The application can also return changes to be made to the validator set,
- as well as a cryptographic digest of its latest state.
-
- Tendermint is designed to enable efficient verification and authentication
- of the latest state of the blockchain. To achieve this, it embeds
- cryptographic commitments to certain information in the block "header".
- This information includes the contents of the block (eg. the transactions),
- the validator set committing the block, as well as the various results returned by the application.
- Note, however, that block execution only occurs _after_ a block is committed.
- Thus, application results can only be included in the _next_ block.
-
- Also note that information like the transaction results and the validator set are never
- directly included in the block - only their cryptographic digests (Merkle roots) are.
- Hence, verification of a block requires a separate data structure to store this information.
- We call this the `State`. Block verification also requires access to the previous block.
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