Major Differences Between Cosmos and Polkadot; Two Distinct Philosophy of Inter-Blockchain
Cosmos and Polkadot adopt similar strategies to realize blockchain interoperability, but there are subtle differences in protocol and design, respectively.
Individual vs Overall Security
Cosmos and Polkadot work in two completely different security modes. In short, Polkadot works as follows:
Parachains (parallel chains) are blockchains in Polkadot networks. These Parachains have their own state machines, they make their own rules and they are individual block producers (collators, proofreaders).
Each Parachain is actually an independent state machine that can take advantage of any type of unique function, consensus algorithms, transaction cost structures, and so on.
In Polkadot networks, all Parachains are subchains of chain called Relay Chain. Relay chain has its own consensus algorithm, GRANDPA consensus, which can quickly finalize blocks on Parachain.The validator in Relay chain has the final say on any state change made by a parachain. The validator may constantly reject blocks created by collators (proofreader, block producer) from a particular parachain and permanently prevent the parachain process from being included in the global state.
So Polkadot attempts to reduce the occurrence of this problem by disrupting the verifier, so that the verifier can randomly verify the parachain, reducing the possibility that a particular verifier will review a particular parachain. In addition, Polkadot also has another type of verifier called Fishermen, who constantly checks whether the verifier has malicious behavior.
In contrast, the structure of Cosmos networks is totally different:
In Cosmos networks, each blockchain is independent and self-protective, rather than using a local/global mode like Polkadot to ensure security. Each block chain will run its own consensus mechanism, and the verifier of each chain is only responsible for ensuring the security of the chain.
Compared with Polkadot structure, we can find that the biggest difference of Cosmos is that the security of each zone (independent blockchain) is guaranteed only by the verifier of this blockchain. If a zone wants high security, it will need to add more validators, which may be difficult for small applications.
Governance & Membership
The second difference between Polkadot and Cosmos is their governance and membership. In Polkadot networks, there is only one Relay Chain and a certain number of Parachains (supported by the Verifier of Relay Chain). Currently, the Polkadot network is expected to accommodate 100 parachains, but this number may increase or decrease in the future.
The Polkadot network allocates parachain slots through an auction mechanism — the highest bidder will be able to obtain a slot by locking DOT (the original token of the Polkadot network) in a PoS system. On the other hand, there is no fixed membership rule in Cosmos networks – anyone can build a Hub chain or a Zone chain. Hub itself is a sovereign (control) block chain, built to connect with other blockchains. One example is the Cosmos Hub recently built by the Tendermint team, Another example is the Iris Hub that is planned to link those block chains working mainly in China and other parts of Asia.
In Polkadot networks, governance decisions are determined by the number of DOT tokens held by voters. There will be a formal voting mechanism on the chain, but this has not been decided yet.
Cosmos networks do not have a unitary governance process. Each Hub chain and Zone chain has its own governance process, and there is no central rule set applicable to the whole block chain network.
Another difference between Polkadot and Cosmos is their structure and design goals in Inter-blockchain communication protocols.
Polkadot’s goal is to deliver arbitrary messages between Parachains, which means that Parachain A can invoke smart contracts in Parachain B, transfer token between two chains, or any other type of communication. On the other hand, Cosmos focuses on asset transfer among blockchain, which is a simpler protocol.
Polkadot uses the concept of Fishermen, a bounty hunter who monitors malicious activities on the Polkadot network. In a sense, this is the “second line of defense” of the Polkadot network against malicious acts. If the validator of a particular Parachain determines an invalid block, Fishermen can submit a proof to Relay Chain and effectively roll back the entire state of the Polkadot network and related Parachains.
Cosmos, by contrast, takes a completely different approach to inter-blockchain communication. Because each chain has its own verifier in Cosmos network, ther may be some “malicious” Zone chains containing collusion verifiers, which means Zone A needs to trust the verifiers in Cosmos Hub and Zone B when one Zone chain wants to communicate with another Zone chain.
Substrate vs Cosmos SDK
Both Polkadot and Cosmos provide a software development package, namely Substrate and Cosmos SDK. The purpose of these two development packages is to make it easier for developers to start building their own blockchain, including various instant modules (including governance module), staking module, authentication module and so on.
The main difference between the two development packages is that Cosmos SDK supports the Go language, while Substrate is more flexible as it supports any WASM (Web Assembly) compatible language. Both packages are new frameworks for building blockchain and will be equipped with more function in the next few years.
If the problem of data availability in Polkadot can be solved, inter-blockchain messaging under shared security will become easier. But Cosmos has more flexible for specific projects, such as Binance. And Cosmos focuses on providing easier asset transfers.