A plasma chain is a separate blockchain that is anchored to the main Ethereum chain, and uses fraud proofs (like optimistic rollups) to arbitrate disputes. These chains are sometimes referred to as "child" chains as they are essentially smaller copies of the Ethereum Mainnet. Merkle trees enable creation of a limitless stack of these chains that can work to offload bandwidth from the parent chains (including Mainnet). These derive their security through fraud proofs, and each child chain has its own mechanism for block validation.
You should have a good understanding of all the foundational topics and a high-level understanding of Ethereum scaling. Implementing scaling solutions such as Plasma is an advanced topic as the technology is less battle-tested, and continues to be researched and developed.
|High throughput, low cost per transaction.||Does not support general computation. Only basic token transfers, swaps, and a few other transaction types are supported via predicate logic.|
|Good for transactions between arbitrary users (no overhead per user pair if both are established on the plasma chain)||Need to periodically watch the network (liveness requirement) or delegate this responsibility to someone else to ensure the security of your funds.|
|Plasma chains can be adapted to specific use-cases that are unrelated to the main chain. Anyone, including businesses, can customize Plasma smart contracts to provide scalable infrastructure that works in different contexts.||Relies on one or more operators to store data and serve it upon request.|
|Withdrawals are delayed by several days to allow for challenges. For fungible assets this can be mitigated by liquidity providers, but there is an associated capital cost.|
|If too many users try to exit simultaneously, Ethereum Mainnet could get congested.|
Plasma, sidechains, and sharding are fairly similar because they all connect to Ethereum Mainnet in some way. However, the level and strength of these connections vary, which affects the security properties of each scaling solution.
A sidechain is an independently operated blockchain connected to Ethereum Mainnet via a two-way bridge. Bridges allow users to exchange tokens between the two blockchains to transact on the sidechain, reducing congestion on Ethereum Mainnet and improving scalability. Sidechains use a separate consensus mechanism and are typically much smaller than Ethereum Mainnet. As a result, bridging assets to these chains involves increased risk; given the lack of security guarantees inherited from Ethereum Mainnet in the sidechain model, users risk the loss of funds in an attack on the sidechain.
Conversely, plasma chains derive their security from Mainnet. This makes them measurably more secure than sidechains. Both sidechains and plasma chains can have different consensus protocols, but the difference is that plasma chains publish Merkle roots for each block on Ethereum Mainnet. Block roots are small pieces of information we can use to verify information about transactions that happen on a plasma chain. If an attack happens on a plasma chain, users can safely withdraw their funds back to Mainnet using the appropriate proofs.
Both plasma chains and shard chains periodically publish cryptographic proofs to Ethereum Mainnet. However, both have different security properties.
Shard chains commit "collation headers" to Mainnet containing detailed information about each data shard. Nodes on Mainnet verify and enforce the validity of data shards, reducing the possibility of invalid shard transitions and protecting the network against malicious activity.
Plasma is different because Mainnet only receives minimal information about the state of child chains. This means Mainnet cannot effectively verify transactions conducted on child chains, making them less secure.
Multiple projects provide implementations of Plasma that you can integrate into your dapps:
- EthHub on Plasma
- Learn Plasma
- A quick reminder of what "shared security" means and why it's so important
- Sidechains vs Plasma vs Sharding
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