Special thanks to @Slamper for a series of bug reports in our [bug bounty
program](https://hackerone.com/tendermint) which are fixed in this release.
This release is primarily about adding Version fields to various data structures,
optimizing consensus messages for signing and verification in
restricted environments (like HSMs and the Ethereum Virtual Machine), and
aligning the consensus code with the [specification](https://arxiv.org/abs/1807.04938).
It also includes our first take at a generalized merkle proof system, and
changes the length of hashes used for hashing data structures from 20 to 32
bytes.
See the [UPGRADING.md](UPGRADING.md#v0.26.0) for details on upgrading to the new
version.
Please note that we are still making breaking changes to the protocols.
While the new Version fields should help us to keep the software backwards compatible
even while upgrading the protocols, we cannot guarantee that new releases will
be compatible with old chains just yet. We expect there will be another breaking
release or two before the Cosmos Hub launch, but we will otherwise be paying
increasing attention to backwards compatibility. Thanks for bearing with us!
### BREAKING CHANGES:
* CLI/RPC/Config
* [config] [\#2232](https://github.com/tendermint/tendermint/issues/2232) Timeouts are now strings like "3s" and "100ms", not ints
* [config] [\#2505](https://github.com/tendermint/tendermint/issues/2505) Remove Mempool.RecheckEmpty (it was effectively useless anyways)
* [config] [\#2490](https://github.com/tendermint/tendermint/issues/2490) `mempool.wal` is disabled by default
* [privval] [\#2459](https://github.com/tendermint/tendermint/issues/2459) Split `SocketPVMsg`s implementations into Request and Response, where the Response may contain a error message (returned by the remote signer)
* [state] [\#2644](https://github.com/tendermint/tendermint/issues/2644) Add Version field to State, breaking the format of State as
encoded on disk.
* [rpc] [\#2298](https://github.com/tendermint/tendermint/issues/2298) `/abci_query` takes `prove` argument instead of `trusted` and switches the default
behaviour to `prove=false`
* [rpc] [\#2654](https://github.com/tendermint/tendermint/issues/2654) Remove all `node_info.other.*_version` fields in `/status` and
`VoteTypeXxx` are now of type `SignedMsgType byte` and named `XxxType`, eg.
`PrevoteType`, `PrecommitType`.
* [types] [\#2636](https://github.com/tendermint/tendermint/issues/2636) Rename fields in ConsensusParams to remove `Params` suffixes
* [types] [\#2735](https://github.com/tendermint/tendermint/issues/2735) Simplify Proposal message to align with spec
* Blockchain Protocol
* [crypto/tmhash] [\#2732](https://github.com/tendermint/tendermint/issues/2732) TMHASH is now full 32-byte SHA256
* All hashes in the block header and Merkle trees are now 32-bytes
* PubKey Addresses are still only 20-bytes
* [state] [\#2587](https://github.com/tendermint/tendermint/issues/2587) Require block.Time of the fist block to be genesis time
* [state] [\#2644](https://github.com/tendermint/tendermint/issues/2644) Require block.Version to match state.Version
* [types] Update SignBytes for `Vote`/`Proposal`/`Heartbeat`:
* [\#2459](https://github.com/tendermint/tendermint/issues/2459) Use amino encoding instead of JSON in `SignBytes`.
* [\#2598](https://github.com/tendermint/tendermint/issues/2598) Reorder fields and use fixed sized encoding.
* [\#2598](https://github.com/tendermint/tendermint/issues/2598) Change `Type` field from `string` to `byte` and use new
`SignedMsgType` to enumerate.
* [types] [\#2730](https://github.com/tendermint/tendermint/issues/2730) Use
same order for fields in `Vote` as in the SignBytes
* [types] [\#2732](https://github.com/tendermint/tendermint/issues/2732) Remove the address field from the validator hash
* [types] [\#2644](https://github.com/tendermint/tendermint/issues/2644) Add Version struct to Header
* [types] [\#2609](https://github.com/tendermint/tendermint/issues/2609) ConsensusParams.Hash() is the hash of the amino encoded
struct instead of the Merkle tree of the fields
* [types] [\#2670](https://github.com/tendermint/tendermint/issues/2670) Header.Hash() builds Merkle tree out of fields in the same
order they appear in the header, instead of sorting by field name
* [types] [\#2682](https://github.com/tendermint/tendermint/issues/2682) Use proto3 `varint` encoding for ints that are usually unsigned (instead of zigzag encoding).
* [types] [\#2636](https://github.com/tendermint/tendermint/issues/2636) Add Validator field to ConsensusParams
(Used to control which pubkey types validators can use, by abci type).
Add `Type` field to `Proposal` and use same order of fields as in the
SignBytes for both `Proposal` and `Vote`
* [p2p] [\#2654](https://github.com/tendermint/tendermint/issues/2654) Add `ProtocolVersion` struct with protocol versions to top of
DefaultNodeInfo and require `ProtocolVersion.Block` to match during peer handshake
### FEATURES:
- [abci] [\#2557](https://github.com/tendermint/tendermint/issues/2557) Add `Codespace` field to `Response{CheckTx, DeliverTx, Query}`
- [abci] [\#2662](https://github.com/tendermint/tendermint/issues/2662) Add `BlockVersion` and `P2PVersion` to `RequestInfo`
- [crypto/merkle] [\#2298](https://github.com/tendermint/tendermint/issues/2298) General Merkle Proof scheme for chaining various types of Merkle trees together
This release is primarily about adding Version fields to various data structures,
optimizing consensus messages for signing and verification in
restricted environments (like HSMs and the Ethereum Virtual Machine), and
aligning the consensus code with the [specification](https://arxiv.org/abs/1807.04938).
It also includes our first take at a generalized merkle proof system.
See the [UPGRADING.md](UPGRADING.md#v0.26.0) for details on upgrading to the new
version.
Please note that we are still making breaking changes to the protocols.
While the new Version fields should help us to keep the software backwards compatible
even while upgrading the protocols, we cannot guarantee that new releases will
be compatible with old chains just yet. Thanks for bearing with us!
Friendly reminder, we have a [bug bounty program](https://hackerone.com/tendermint).
### BREAKING CHANGES:
* CLI/RPC/Config
* [config] [\#2232](https://github.com/tendermint/tendermint/issues/2232) timeouts as time.Duration, not ints
* [config] [\#2505](https://github.com/tendermint/tendermint/issues/2505) Remove Mempool.RecheckEmpty (it was effectively useless anyways)
* [config] [\#2490](https://github.com/tendermint/tendermint/issues/2490) `mempool.wal` is disabled by default
* [privval] [\#2459](https://github.com/tendermint/tendermint/issues/2459) Split `SocketPVMsg`s implementations into Request and Response, where the Response may contain a error message (returned by the remote signer)
* [state] [\#2644](https://github.com/tendermint/tendermint/issues/2644) Add Version field to State, breaking the format of State as
encoded on disk.
* [rpc] [\#2298](https://github.com/tendermint/tendermint/issues/2298) `/abci_query` takes `prove` argument instead of `trusted` and switches the default
behaviour to `prove=false`
* [rpc] [\#2654](https://github.com/tendermint/tendermint/issues/2654) Remove all `node_info.other.*_version` fields in `/status` and
`/net_info`
* Apps
* [abci] [\#2298](https://github.com/tendermint/tendermint/issues/2298) ResponseQuery.Proof is now a structured merkle.Proof, not just
arbitrary bytes
* [abci] [\#2644](https://github.com/tendermint/tendermint/issues/2644) Add Version to Header and shift all fields by one
* [abci] [\#2662](https://github.com/tendermint/tendermint/issues/2662) Bump the field numbers for some `ResponseInfo` fields to make room for
`AppVersion`
* Go API
* [config] [\#2232](https://github.com/tendermint/tendermint/issues/2232) timeouts as time.Duration, not ints
* [crypto/merkle & lite] [\#2298](https://github.com/tendermint/tendermint/issues/2298) Various changes to accomodate General Merkle trees
* [crypto/merkle] [\#2595](https://github.com/tendermint/tendermint/issues/2595) Remove all Hasher objects in favor of byte slices
* [crypto/merkle] [\#2635](https://github.com/tendermint/tendermint/issues/2635) merkle.SimpleHashFromTwoHashes is no longer exported
* [types] [\#2298](https://github.com/tendermint/tendermint/issues/2298) Remove `Index` and `Total` fields from `TxProof`.
* [types] [\#2598](https://github.com/tendermint/tendermint/issues/2598) `VoteTypeXxx` are now of type `SignedMsgType byte` and named `XxxType`, eg. `PrevoteType`,
`PrecommitType`.
* Blockchain Protocol
* [abci] [\#2636](https://github.com/tendermint/tendermint/issues/2636) Add ValidatorParams field to ConsensusParams.
(Used to control which pubkey types validators can use, by abci type)
* [types] Update SignBytes for `Vote`/`Proposal`/`Heartbeat`:
* [\#2459](https://github.com/tendermint/tendermint/issues/2459) Use amino encoding instead of JSON in `SignBytes`.
* [\#2598](https://github.com/tendermint/tendermint/issues/2598) Reorder fields and use fixed sized encoding.
* [\#2598](https://github.com/tendermint/tendermint/issues/2598) Change `Type` field fromt `string` to `byte` and use new
`SignedMsgType` to enumerate.
* [types] [\#2512](https://github.com/tendermint/tendermint/issues/2512) Remove the pubkey field from the validator hash
* [types] [\#2644](https://github.com/tendermint/tendermint/issues/2644) Add Version struct to Header
* [types] [\#2609](https://github.com/tendermint/tendermint/issues/2609) ConsensusParams.Hash() is the hash of the amino encoded
struct instead of the Merkle tree of the fields
* [state] [\#2587](https://github.com/tendermint/tendermint/issues/2587) Require block.Time of the fist block to be genesis time
* [state] [\#2644](https://github.com/tendermint/tendermint/issues/2644) Require block.Version to match state.Version
* [types] [\#2670](https://github.com/tendermint/tendermint/issues/2670) Header.Hash() builds Merkle tree out of fields in the same
order they appear in the header, instead of sorting by field name
* [types] [\#2682](https://github.com/tendermint/tendermint/issues/2682) Use proto3 `varint` encoding for ints that are usually unsigned (instead of zigzag encoding).
* P2P Protocol
* [p2p] [\#2654](https://github.com/tendermint/tendermint/issues/2654) Add `ProtocolVersion` struct with protocol versions to top of
DefaultNodeInfo and require `ProtocolVersion.Block` to match during peer handshake
### FEATURES:
- [abci] [\#2557](https://github.com/tendermint/tendermint/issues/2557) Add `Codespace` field to `Response{CheckTx, DeliverTx, Query}`
- [abci] [\#2662](https://github.com/tendermint/tendermint/issues/2662) Add `BlockVersion` and `P2PVersion` to `RequestInfo`
- [crypto/merkle] [\#2298](https://github.com/tendermint/tendermint/issues/2298) General Merkle Proof scheme for chaining various types of Merkle trees together