The Blockchain Trilemma: Fast, Secure, and Scalable Networks

What Is the Blockchain Trilemma?

While blockchain technology is proving its remarkable utility in industries ranging from finance to art, the underlying structure of decentralized networks comes with unique challenges when compared to centralized networks. As early as the 1980s, computer scientists developed what’s called the CAP theorem to articulate perhaps the most major of these challenges. According to the CAP theorem, decentralized data stores — of which blockchain is an iteration — can only provide two of three guarantees simultaneously: consistency, availability, and partition tolerance (CAP). In the context of modern distributed networks, this theorem has evolved into the Blockchain Trilemma — the popular belief that public blockchains must sacrifice either security, decentralization, or scalability.

Unlike the client-server relationship that dominates central network infrastructures, public blockchain networks utilize decentralized consensus mechanisms. Public blockchains manage a widely distributed network of nodes to achieve data consensus over an infrastructure that is resilient to outside attack while maintaining transparency and equitable, open access. It’s a challenge. For example: while Bitcoin is decentralized and secure, it is only able to process approximately seven transactions per second (TPS). Enterprise blockchains like Hyperledger’s Fabric are secure and can handle high transactional throughput, but are centralized, with a highly limited number of consensus-achieving nodes. Blockchains that are fast and decentralized — but more insecure — are vulnerable to hacks that are untenable in the long-term.

Achieving a network that features watertight security over a widely decentralized network while being able to manage internet-scale transactional throughput is the holy grail of blockchain tech. A global community of businesses, start-ups, and technologists are feverishly developing Layer-1 and Layer-2 solutions that are solving this Blockchain Trilemma. Layer 1 refers to the base layer, or primary layer, of a blockchain network. Layer 2 refers to various tech optimizations and products that can be built on top of existing blockchain networks, usually to increase their scalability. Achieving the right balance between the two layers could act as an explosive catalyst for the adoption of blockchain tech and the growth of decentralized networks.

Before we can begin to decipher potential solutions, it’s important to understand each component of the Blockchain Trilemma.

What Is Decentralization?

Decentralization is the central ethos of blockchain technology and drives projects across the ecosystem. Applying decentralized processes and tech eliminates the role of intermediaries across industries and manifests in many different ways. For example: by removing banking institutions from financial instruments, decentralized finance (DeFi) platforms, rather than intermediaries, are able to distribute profits and governance to users and the wider community. On an even more foundational level, decentralized networks crowdsource consensus, meaning that no one entity can control or censor the data that transacts through it. However, achieving optimal decentralization tends to decrease network throughput. As more miners secure a Proof-of-Work (PoW) network through consensus, transaction speeds may drop — which is considered a hurdle to widespread adoption.

What Is Blockchain Security?

To increase network throughput on a blockchain network, there's an incentive to reduce the distribution of blockchain nodes either geographically, in number, or both. However, this pivot toward greater centralization reduces security on PoW networks. When consensus is achieved on an open network with limited nodal distribution, a 51% attack is more probable as hackers can amass the required hashing power with greater ease. By overwhelming a network, hackers can hijack the network and manipulate transactions for financial gain. For example: In August 2020, the Ethereum Classic (ETC) blockchain — which is a fork of Ethereum (ETH) —  suffered three 51% attacks that reorganized more than 4,000 blocks. This allowed the perpetrators to manipulate data and double spend its ETC currency, resulting in the loss of millions of dollars in value on the network. Blockchain security is a critical network aspect that cannot be compromised.

What Is Scalability?

Scalability with regard to a blockchain protocol refers to the blockchain’s ability to support high transactional throughput and future growth. This means that as use cases and adoption accelerate, the performance of the blockchain won’t suffer. Blockchains that perform poorly as adoption increases are said to lack scalability. The Blockchain Trilemma tells us that greater scalability is possible, but security, decentralization, or both, will suffer as a consequence. Scalability is the only way for blockchain networks to reasonably compete with legacy, centralized platforms whose network settlement times and usability are, at this point, far superior. While many blockchain platforms have established decentralization and security, achieving scalability remains the major challenge for today’s leading decentralized networks.

So how can we solve the Blockchain Trilemma and achieve decentralization, security, and scalability simultaneously? The answer comes in the form of Layer-1 and Layer-2 solutions.

Solving the Blockchain Trilemma: Layer 1

In the decentralized ecosystem, Layer 1 refers to blockchain protocols like Bitcoin, Litecoin, and Ethereum. There are a number of methods currently in development or practice that seek to improve the scalability of blockchain networks directly.

• Consensus Protocol Improvements: Proof of Work is the consensus protocol currently in use on popular blockchain networks like Bitcoin. Although PoW is secure, it can be slow. For instance, Bitcoin only achieves seven TPS. That’s why many blockchain networks — perhaps most notably Ethereum’s upgrade to Ethereum 2.0 — favor the Proof-of-Stake (PoS) consensus mechanism. Instead of requiring miners to solve cryptographic algorithms using substantial computing power, the PoS consensus protocol determines validator status based on a stake in the network. This is expected to dramatically and fundamentally increase the capacity of the Ethereum network, while increasing decentralization and ensuring security.

• Sharding: Sharding is adapted from distributed databases and has become one of the most popular Layer-1 scaling solutions, despite its somewhat experimental nature within the blockchain sector. Sharding breaks transactions into smaller datasets called "shards." These shards are simultaneously processed in parallel by the network, allowing for sequential work on numerous transactions simultaneously. Further, instead of having each network node hold a copy of every block from its genesis block to present, this information could be split and held by different nodes, with each remaining consistent with itself. Shards provide proofs to the mainchain and interact with one another to share addresses, balances, and general states using cross-shard communication protocols. Ethereum 2.0 is one high-profile blockchain protocol that’s exploring the use of shards, along with Zilliqa, Tezos, and Qtum.

Solving the Blockchain Trilemma: Layer 2

In blockchain, Layer 2 refers to a network or technology that operates atop an underlying blockchain protocol to improve its scalability and efficiency. For instance, Bitcoin is a Layer-1 protocol, and the Lightning Network is a Layer-2 solution built to improve transaction speeds on the Bitcoin network. Layer-2 protocols have undergone immense growth in recent years, and could be the most efficient way to overcome scalability challenges for PoW networks in particular.

• Nested Blockchains: A nested blockchain is a decentralized network infrastructure that utilizes a main blockchain to set parameters for the broader network, while executions are undertaken on an interconnected web of secondary chains. Multiple blockchain levels are built on this mainchain, with these levels using a parent-child connection. The parent chain delegates work to child chains, which process and return it to the parent after completion. The underlying base blockchain does not take part in network functions unless dispute resolution is necessary. The OMG Plasma project is an example of Layer-2 nested blockchain infrastructure that is utilized atop Layer-1 Ethereum to facilitate faster and cheaper transactions. The distribution of work under this model reduces the processing burden on the mainchain to exponentially improve scalability.

• State Channels: A state channel facilitates two-way communication between a blockchain and off-chain transactional channels using various mechanisms to improve overall transaction capacity and speed. A state channel does not require immediate miner involvement to validate the transaction. Instead, it is a network-adjacent resource that is sealed off by using a multi-signature or smart contract mechanism. When a transaction or batch of transactions is complete on a state channel, the final “state” of the “channel” and all its inherent transitions are recorded to the underlying blockchain. The Liquid Network, Celer, Bitcoin Lightning, and Ethereum's Raiden Network are examples of state channels. In the trilemma tradeoff, state channels sacrifice some degree of decentralization to achieve greater scalability.

• Sidechains: A sidechain is a blockchain-adjacent transactional chain used for large batch transactions. Sidechains use an independent consensus mechanism to that of the original chain, which can be optimized for speed and scalability. Utility tokens are often used as part of the data transferral mechanism between side and mainchains. The primary role of the mainchain is to maintain overall security and dispute resolution. Sidechains differentiate from state channels in a number of integral ways. First, sidechain transactions aren’t private between participants — they are publicly recorded to the ledger. Further, sidechain security breaches do not affect the mainchain or other sidechains. Establishing a sidechain requires substantial effort as infrastructure is built from the ground up.

Solving the Blockchain Trilemma

Although the Blockchain Trilemma presents significant challenges to adopting blockchain technology, emerging solutions may solve the puzzle. The goal is to find an effective balance between network security, decentralization, and scalability. While the CAP theorem has held true for almost four decades, the implementation of Layer-1 and Layer-2 solutions — alongside the emergence of Proof-of-Stake systems — is shifting the paradigm toward decentralized blockchain networks that are at once distributed, secure, and scalable.