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Fundamentals: What's the Deal With Blockchain Bridges?

Alex Bączkowski

Content Writer

Apr 5, 2023

7 min read

Blockchains are isolated systems by nature, so we need to build special constructions called bridges to get them to communicate with each other. Aleph Zero will be bridging to several ecosystems as we expand our functionality into the multichain world, but first, let’s look at how this process works. 

The future of the blockchain sphere is in creating a cooperative ecosystem in which different projects specializing in their own niche work together to provide a wide range of services as we move to the Web3 model. Gone are the days of blockchain developers dreaming of creating a single system that will cater to all of its users’ needs, instead opting for a multichain scenario powered by structures called bridges. This worldview is also close to the Aleph Zero team as we aim to connect Aleph Zero to other blockchains allowing our users to reap the unique benefits provided by the solutions offered by other chains. So let’s dive in and explore:

  • Why are bridges required? 
  • How do they work? 
  • And where is Aleph Zero bridging to? 

Why do we need bridges? 

By definition, blockchains are built to be standalone systems that are governed by their respective consensus protocol, that is, the code that determines how blocks are created and how transaction validity is ensured. Each blockchain can support its native token, NFTs, and other assets. Additionally, those blockchains that offer smart contracts (for example, Ethereum and Aleph Zero) provide developers and users the possibility to build complex applications related to gaming, DeFi, and other Web3 services. This is all well and good as long as we remain in the confines of one ecosystem, as these apps can communicate with each other without delay and provide users with a complex system of interoperable tools from which they can benefit. However, we run into one of the fundamental challenges facing the Web3 space in that blockchains are, by design, isolated systems that cannot communicate with the outside world. 

This may seem counterintuitive, seeing that blockchains are hosted on the Internet, and we’ve become accustomed to Web2 systems seamlessly working together. To illustrate how blockchains work, let’s try to imagine the following: 

Picture a blockchain as an incredibly reliable computer with heaps of storage space that is virtually indestructible by design. So where’s the catch? This computer has NO INTERNET ACCESS! This means that whatever programs it runs cannot interact with other computers (blockchains) and their respective programs. 

Fortunately, there are solutions to this challenge! Interoperability between blockchains is incredibly important for the future of the space, as we want users to be free to use whatever element of the Web3 world they need at the moment. So what are we up against, and why is bridging blockchain ecosystems such a research and work-intensive process? 

The Challenge of Getting Blockchains to Communicate with Each Other 

Blockchains, by design, are decentralized systems, and it is this most characteristic feature that is at the heart of the problem we are describing. Because of their decentralized nature, decisions on a blockchain are made not by one central authority but by a number of parties who cooperate and reach a consensus on every decision made by the chain. This makes it inherently hard to pass information from one chain to another because there is no single entity that could relay information between two chains and be trusted to do it correctly. 

Let’s assume we want to pass some data from chain A to B. For this data to be accepted as valid, chain B would somehow need to validate the data that is being passed from chain A. This would require making sure that chain A accepted the data according to the consensus rules governing chain B. This would be a complicated task by itself, but it becomes even more headache-inducing when we take into account that almost every chain uses a different consensus protocol. This would mean that each “connection” between two chains would require them to adopt a completely different set of rules.

How Bridges Make Interoperability Possible 

A blockchain bridge is a special protocol that allows us to connect two blockchains together, enabling us to take advantage of the unique apps and features that define each ecosystem. At its most basic level, a bridge between chains A and B consists of two parts: 

  • A -> B message passing
  • B -> A message passing

Both of these channels allow us only to send messages one way. This system allows users in both ecosystems to know what’s going on in each network. 

At this point, a natural question to pose is how does this system deal with tokens, namely, is it possible to send tokens through a bridge? The short answer to this question is “no,” BUT we do have a workaround that, for all intents and purposes, works through a process called token wrapping. 

What is Token Wrapping? 

From a technical standpoint sending tokens from one blockchain to another is impossible simply because each blockchain is responsible for tracking the ownership of its native token—

period. This is where token wrapping comes into play. To have wrapped tokens, we need smart contracts on both chains and a bridge allowing message passing between two contracts on these chains.

Let’s imagine that Alice has an account on Ethereum and Aleph Zero and that she would like to move 1 ETH to the Aleph Zero chain. To do so, she would have to: 

  1. Send 1 ETH to a special contract on Ethereum. 
  2. This contract freezes the 1 ETH and sends a message via the Ethereum ->Aleph Zero bridge that states that “Alice just froze 1 ETH. Please create an equal amount of wrapped ETH for her.”
  3. Once the Aleph Zero ecosystem receives the message, Alice will be able to withdraw 1 wrapped ETH on Aleph Zero. At this point, Alice can use this wrapped asset to explore the Aleph Zero ecosystem and its use cases. 

At this point, Alice, in a sense, holds 1ETH on Aleph Zero. While technically, this is slightly incorrect, this is still a good description of what occurred. This process of wrapping and unwrapping works both ways, of course, so it is absolutely possible for Alice to send a message to the Ethereum network to redeem her original 1 ETH. 

It’s Hard to Get Bridges Right 

Due to their incredibly complex nature, years of research went into designing blockchain bridges, and as with most technological developments, mistakes were made and hard lessons learned. Unfortunately, weak points in bridges make them prone to hacks. Most commonly, thee are bugs in the smart contracts that black hat hackers became aware of and keenly took advantage of. The year 2022 alone saw approximately $2.1 billion being stolen in bridge hacks. These setbacks have resulted, though, in better designs that have greater security guarantees to keep users safe. However, we don’t want to paint a completely gloomy picture of these solutions because: 

  1. Bridges are key to Web3 interoperability. 
  2. Most errors leading to hacks are rooted in human error, and with time both bugs in the code will be eliminated and protocols enforced to eliminate these obstacles. 

Crucial elements to achieve these goals are trustless security systems and smart contract audits to prevent exploitable bugs from creeping into the system. 

All Bridges Lead to Aleph Zero 

The team of Cardinal Cryptography has already identified the first batch of ecosystems to which we will want to connect the Aleph Zero network in our drive to increase interoperability and allow for liquidity and users to migrate freely.

A milestone event in this regard was winning an auction for a parachain slot in the Polkadot ecosystem in January 2023, providing an invaluable gateway to this burgeoning network of users and applications. Future plans include bridging to Cosmos and Ethereum. As we slowly expand into the world of interconnected blockchains, we will take the utmost care and exercise every precaution to ensure the safety of our bridges and the users who will use them on a daily basis. 

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