2017-12-26 18:43:03 -05:00
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# Tendermint Specification
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This is a markdown specification of the Tendermint blockchain.
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2018-01-21 18:19:38 -05:00
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It defines the base data structures, how they are validated,
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and how they are communicated over the network.
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2017-12-26 18:43:03 -05:00
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2018-01-19 17:51:09 -05:00
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XXX: this spec is a work in progress and not yet complete - see github
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[isses](https://github.com/tendermint/tendermint/issues) and
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[pull requests](https://github.com/tendermint/tendermint/pulls)
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for more details.
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If you find discrepancies between the spec and the code that
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do not have an associated issue or pull request on github,
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please submit them to our [bug bounty](https://tendermint.com/security)!
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2017-12-26 18:43:03 -05:00
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2018-01-19 17:51:09 -05:00
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## Contents
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2018-01-21 18:19:38 -05:00
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### Data Structures
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2018-01-19 17:51:09 -05:00
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- [Overview](#overview)
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2017-12-26 18:43:03 -05:00
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- [Encoding and Digests](encoding.md)
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- [Blockchain](blockchain.md)
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- [State](state.md)
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2018-01-21 18:19:38 -05:00
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### P2P and Network Protocols
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- [The Base P2P Layer](p2p/README.md): multiplex the protocols ("reactors") on authenticated and encrypted TCP conns
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- [Peer Exchange (PEX)](pex/README.md): gossip known peer addresses so peers can find eachother
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- [Block Sync](block_sync/README.md): gossip blocks so peers can catch up quickly
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- [Consensus](consensus/README.md): gossip votes and block parts so new blocks can be committed
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- [Mempool](mempool/README.md): gossip transactions so they get included in blocks
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- [Evidence](evidence/README.md): TODO
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### More
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- [Light Client](light_client/README.md): TODO
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- [Persistence](persistence/README.md): TODO
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2017-12-26 18:43:03 -05:00
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2017-12-27 15:14:49 -05:00
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## Overview
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Tendermint provides Byzantine Fault Tolerant State Machine Replication using
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hash-linked batches of transactions. Such transaction batches are called "blocks".
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Hence Tendermint defines a "blockchain".
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Each block in Tendermint has a unique index - its Height.
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A block at `Height == H` can only be committed *after* the
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block at `Height == H-1`.
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Each block is committed by a known set of weighted Validators.
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Membership and weighting within this set may change over time.
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Tendermint guarantees the safety and liveness of the blockchain
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so long as less than 1/3 of the total weight of the Validator set
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is malicious.
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A commit in Tendermint is a set of signed messages from more than 2/3 of
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the total weight of the current Validator set. Validators take turns proposing
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blocks and voting on them. Once enough votes are received, the block is considered
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committed. These votes are included in the *next* block as proof that the previous block
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was committed - they cannot be included in the current block, as that block has already been
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created.
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Once a block is committed, it can be executed against an application.
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The application returns results for each of the transactions in the block.
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The application can also return changes to be made to the validator set,
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as well as a cryptographic digest of its latest state.
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Tendermint is designed to enable efficient verification and authentication
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of the latest state of the blockchain. To achieve this, it embeds
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cryptographic commitments to certain information in the block "header".
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This information includes the contents of the block (eg. the transactions),
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the validator set committing the block, as well as the various results returned by the application.
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Note, however, that block execution only occurs *after* a block is committed.
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Thus, application results can only be included in the *next* block.
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Also note that information like the transaction results and the validator set are never
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directly included in the block - only their cryptographic digests (Merkle roots) are.
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Hence, verification of a block requires a separate data structure to store this information.
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We call this the `State`. Block verification also requires access to the previous block.
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