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Cosmos is the hub to almost 50 blockchains based on the Tendermint consensus engine and Inter-Blockchain Communication (IBC) protocol. It is also one of the earliest proponents for cross-chain communication and defined the first set of communication specificiations24. From a purely technical point of view, the signature scheme for signing blocks, Ed25519, is also often used in many other protocols, such as NEAR.

Cosmos Hub itself has 175 validators25 and is built upon Tendermint, in which validators sign blocks using EdDSA on Curve25519 (i.e., Ed25519)26.

Consensus Mechanism

For a deep dive on Tendemints Consensus, please read The latest gossip on BFT consensus: The paper presents Tendermint, a new protocol for ordering events in a distributed network under adversarial conditions.

Following is an excerpt from What is Tendermint

Tendermint is an easy-to-understand, mostly asynchronous, BFT consensus protocol. The protocol follows a simple state machine that looks like this:


Participants in the protocol are called validators; they take turns proposing blocks of transactions and voting on them. Blocks are committed in a chain, with one block at each height. A block may fail to be committed, in which case the protocol moves to the next round, and a new validator gets to propose a block for that height. Two stages of voting are required to successfully commit a block; we call them pre-vote and pre-commit. A block is committed when more than 2/3 of validators pre-commit for the same block in the same round.

There is a picture of a couple doing the polka because validators are doing something like a polka dance. When more than two-thirds of the validators pre-vote for the same block, we call that a polka. Every pre-commit must be justified by a polka in the same round.

Validators may fail to commit a block for a number of reasons; the current proposer may be offline, or the network may be slow. Tendermint allows them to establish that a validator should be skipped. Validators wait a small amount of time to receive a complete proposal block from the proposer before voting to move to the next round. This reliance on a timeout is what makes Tendermint a weakly synchronous protocol, rather than an asynchronous one. However, the rest of the protocol is asynchronous, and validators only make progress after hearing from more than two-thirds of the validator set. A simplifying element of Tendermint is that it uses the same mechanism to commit a block as it does to skip to the next round.

Assuming less than one-third of the validators are Byzantine, Tendermint guarantees that safety will never be violated - that is, validators will never commit conflicting blocks at the same height. To do this it introduces a few locking rules which modulate which paths can be followed in the flow diagram. Once a validator precommits a block, it is locked on that block. Then,

  1. it must prevote for the block it is locked on
  2. it can only unlock, and precommit for a new block, if there is a polka for that block in a later round

Signing Mechanism

Below is an excerpt from Tendermint Specification

Tendermint uses Protobuf Oneof to distinguish between different types public keys, and signatures. Additionally, for each public key, Tendermint defines an Address function that can be used as a more compact identifier in place of the public key.

Key Types

Each type specifies it’s own pubkey, address, and signature format.


The address is the first 20-bytes of the SHA256 hash of the raw 32-byte public key:

address = SHA256(pubkey)[:20]

The signature is the raw 64-byte ED25519 signature.

Tendermint adopted zip215 for verification of ed25519 signatures.

Note: This change will be released in the next major release of Tendermint-Go (0.35).


The address is the first 20-bytes of the SHA256 hash of the raw 32-byte public key:

address = SHA256(pubkey)[:20]

Following is an excerpt from Tendermint docs: Validator Keys

Currently Tendermint uses Ed25519 (opens new window)keys which are widely supported across the security sector and HSMs.

Code Review



Cryptographic Primitives

general primitives

hash functions


random number generators





Light Client




[24] See Cosmos IBC documentation

[25] See Cosmos Hub overview

[26] See Tendermint Core documentation