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How rollups can improve the efficiency of blockchains
• Originally developed for use in finance, blockchains can potentially be used in several applications. But their development for new applications has been hampered by problems of scale. Now, a technique known as rollups may soon enable blockchains to play a key role in the Internet of Things and online marketplaces.
• This technique allows the delocalization of data and applications to make blockchain technology much easier, paving the way for faster, more powerful and more secure transactions.
• This method can also be used to process data from Internet of Things devices that are integrated into a blockchain.
Scandals such as the resounding collapse of FTX in the fall of 2022 or the bankruptcy of the Mt.Gox bitcoin exchange in February 2014 have tarnished the image of blockchains for the general public, while contributing to the perception that the technology is limited to the field of financiers. Although finance still accounts for a majority of blockchain applications, blockchains can also be used to track food products, manage drone fleets, protect intellectual property and diplomas, and trade surplus renewable energy (Brooklyn Microgrid project in New York). In fact, all transfers of data and instructions between connected entities (devices, services, vehicles, industrial machines) can be managed by blockchains. At least that is the case in theory, but the problem of scaling up this decentralized infrastructure, which is automatically regulated by computers and cryptography, has yet to be solved.
The challenge of processing power
The blocks, which are used to record data about transactions validated by blockchain systems, are limited in size and the speed at which they are created can be painfully slow (a block every ten minutes on Bitcoin, every 14 seconds on Ethereum, and every 30 seconds on Tezos) . As a natural consequence of decentralization, each blockchain node stores the history of all transactions in the chain in a registry that can amount to dozens of gigabytes, far beyond the storage capacity of certain IoT devices. At the same time, methods to validate blocks, in particular schemes, require large amounts of computing power that may not be available on regular IoT devices.
It makes no sense to endlessly store drone positions from a small application on thousands of machines
Then there is the question of the financial costs of validating transactions, which for applications that generate huge amounts of data can be prohibitive. “It makes no sense to endlessly store drone positions from a small application on thousands of machines,” adds Jérôme Lacan, Head of the Department of Complex Systems Engineering at ISAE-SupAéro in Toulouse. Together with his colleague Caroline Chanel and doctoral researcher Thomas Lavaur, Lacan has recently published an article in the journal Sensors on rollups, a solution that aims to overcome these limitations.
One can transaction can confirm thousands of others
Systems of this type are currently very much in vogue in the blockchain world. “The idea is to delocalize some of the data and applications to rollups, which can be placed on local networks, enterprise systems or elsewhere, and organize exchanges between them and the blockchain,” explains Jérôme Lacan. “Transactions take place on the digest and user accounts, which are blocked on the blockchain, are regularly updated.“
Abstract makes use of a cryptographic tool known as a , which transforms incoming data into digests (hashes) weighing only a few bytes. “In a single short transaction, this Merkle tree makes it possible to commit and confirm not one, but thousands of transactions with it, which was not possible before,” writes Daniel Augot, director of research at INRIA (the French National Institute for Research in Digital Science and Technology) in a recent article for the Institut Polytechnique de Paris. The technique also frees up a huge amount of bandwidth on the blockchain.
Added privacy with ZK rollups
For the IoT devices, the researchers at the Institut Supérieur de l’Aéronautique et de l’Espace (SupAéro) have adopted an approach that makes use of what are called ZK (zero-knowledge) rollups. “Using a known program, someone will create a proof that everything has worked as it should, and anyone will be able to check it without having to perform the transaction on the blockchain”, explains Thomas Lavaur. This can be done without including data security. In all transparency, the collection members see the input, but only one member generates the proof. Even better, only the proof has to be submitted to the blockchain, without revealing data about the transactions remaining on the digest, thus ensuring greater privacy.
“It would be relatively easy to use this Uber-type mechanism marketplaces”, points out Jérôme Lacan. “Drivers can post transactions indicating availability and location, while passengers can indicate where they want to go, and all this can be managed with smart contracts whose code is freely available, with clear rules for attributing trips, and predetermined prices, but without any centralized agency.” As it stands, companies take responsibility for rollups and proof generation. However, it is now possible to imagine systems where local groups of users can perform these operations themselves.
