A parachain(parallelizable chain) is a simpler form of blockchain.Blockchains today come in a pretty standard form consisting of two parts. The first part is the consensus algorithm, which provides security. The second part is the state machine, which provides the aspects of the chain that are worth obtaining security over. Ethereum, Bitcoin, Zcash, and others are all secured by variants of Proof-of-Work consensus, but the kinds of transactions and accounts they handle — the things that make up their unique state machine — are all different.


  • Connect chains with distinct state machines and consensus.
  • Support past,present and future.
  • Public and private running in the same network.

Polkadot lets chains pool security resources .
Competition turns into rules based co-operation.

Building Blocks-Technology


-web assembly

-lib p2p

Validity Function: Web Assembly stored on chain in the parachain registry.

Collator nodes: Creates candidate blocks that satisfies the validity function.

Message queues: Candidates must also process incoming and produce outgoing messages.

Relay chain mechanisms

1.Validators – The ones who author a chain of blocks

2.Nominators – They put up stake on behalf of good validators

  1. Collators – Create parachain candidates to give it to validator.

4.Fishermen– Final line of defence watch for misbehaviour of validators.

Ensuring validity

  • Only a basic threshold of validators check each parachain candidate
  • In our security model,bad validators may include bad things
  • Fishermen can issue an on-chain dispute to slash the offending validators.


  • Low barrier to entry:Cheap to become validator
  • Separate Block Production from Finality
  • Make use of blockchain structure

Consensus:Block Production

  • Round-based probabilistically safe system.
  • Large pool of validators with randomly chosen.
  • Authors are aware shortly before their turn.

The workflow of a transaction from one parachain to another would look like this :

1. A user creates a transaction on parachain A to send information to the parachain B.

2.The transaction is sent to one  of parachain A’s collators.

3.The collator makes sure that the transaction is valid and includes it into a block.

4.The collator presents this block, along with a state transition proof to a validator of parachain A.

5.The validator verifies that the received block only contains valid transactions and stakes DOTs on it.

6.When enough nominators have staked their DOTs on the validator, broadcasting its blocks to the relay chain will be authorized.

7.The transaction is executed and the data from A is sent to B.

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