However, before Bitcoin and its imitators came along, "crypto" referred to something else: cryptography, the study of secure digital communication that uses mathematics to hide secrets. And while cryptocurrencies have been grabbing all the attention for the past few years, blockchain technology under the hood was quietly fueling a crypto renaissance.
The most intriguing of these cryptographic breakthroughs involves a mind-boggling tool called a zero-knowledge proof. Zero-knowledge proof-based systems can help address some of the technical limitations of blockchains. But they could also be valuable in ways that have nothing to do with blockchain or cryptocurrency. They could even help us deal with the rising tide of misinformation online by verifying the original sources of content.
Where is Waldo?
A zero-knowledge proof system allows you to prove to someone that you know a secret without revealing the secret itself. Imagine being able to prove that you were old enough to enter a nightclub without revealing your date of birth or any other information on a typical ID card.
Sara Meiklejohn, professor of cryptography and security at University College London, uses a "Where's Waldo?" analogy to explain how a zero knowledge system works. He supposes that he wants to show his friend that he knows Waldo's location on a given page without revealing where he is.
The way crypto works is complicated, but in essence, it's like you both have a copy of the same page in a "Where's Waldo?" book. You cover your copy with a piece of cardboard that is twice as long and twice as wide as the page. He then cuts a hole in the cardboard large enough to reveal enough of Waldo to be unmistakably him. Your friend can't tell exactly where the page behind the cardboard is, but he knows you know the location without learning it himself.
cryptographers Shafi Goldwasser and Silvio Micali introduced the theory behind zero-knowledge proofs in 1985 while at MIT. In 2013, Goldwasser and Micali won the Turing Award, the prestigious award of the Association of Computing Machinery, for contributions to the field of modern cryptography. But it wasn't until a few years later, and three decades after they first came up with the idea, that his most famous invention became more than a theory.
The catalyst was the rise of cryptocurrencies and the underlying blockchain technology. Blockchain developers were looking for something that could do exactly what a zero-knowledge proof can do.
The Bitcoin blockchain is essentially a ledger that uses cryptography and a distributed network of computers to validate and track each transaction. The system's mysterious inventor, Satoshi Nakamoto, called it an alternative payment system "based on cryptographic proofs rather than trust." However, there was a problem with this vision.
In short, blockchains are not private. Users are represented on the blockchain by alphanumeric strings called addresses. To validate a transaction, computers on the network need to know the sender's and recipient's addresses, as well as the amount being transferred, so all of that information needs to be published on the blockchain.
This level of transparency would prevent blockchains from becoming what their enthusiasts dream of creating: a true replacement for the traditional financial system, says Zac Williamson, chief technology officer at Aztec, a startup focused on creating tools for developers that build zero-knowledge proof applications. โPeople won't accept a world where everyone can see how they spend their money, how much they get paid and what their mortgages are,โ he says.
Early blockchain developers were in luck: By the time Bitcoin and its early imitators began to gain traction, academic cryptographers were finally figuring out how to make Goldwasser and Micali's ideas practical. The system they devised is called a zero-knowledge noninteractive succinct knowledge argument, or zk-SNARK. In 2016, a team of cryptocurrency-focused cryptographers implemented zk-SNARK on a blockchain and launched a Bitcoin-like cryptocurrency called Zcash, which allows users to transact privately. Network nodes can verify transactions without revealing any information used to perform the calculation. Since Waldo is on the page, the valid transaction is on the blockchain.
Beyond blockchain
Zcash doesn't have as many users as Bitcoin or some other digital currencies, but it started a "cambrian explosion" of technologies based on zero-knowledge proofs, it says Pratyush Mishrawho recently received his Ph.D. in computer science from the University of California, Berkeley, where he studied with Alexander Church, one of the co-inventors of Zcash. Mishra's PhD research formed the basis of a startup called Come onwho built their own blockchain that uses zero-knowledge proofs.
Another zk-SNARK app powers Tornado Cash, a privacy-focused open-source project that allows users to deposit cryptocurrency and then withdraw it to a different digital address. Zk-SNARKs hide the links between addresses. Last year, the US Treasury placed sanctions on Tornado Cash, alleging that it facilitated money laundering by North Korea. Since Tornado Cash is made up of publicly accessible programs that no one owns or controls, however, the government cannot remove it unless it can somehow shut down the larger Ethereum blockchain that Tornado Cash runs on. The situation illustrates why blockchain applications are far from dead.
It also helps show the versatility of zero-knowledge proofs, even in applications far beyond blockchain and digital currencies. For example, a company could use zero-knowledge proofs to show that its machine learning model meets certain criteria for accuracy or fairness without sharing the actual model, he says. dawn song, professor of computer science at UC Berkeley. A startup he founded, oasis laboratoriesaims to commercialize this idea.
Stanford researchers recently described a system that is designed to combat misinformation by adding zero-knowledge proof to digital images in the media. It is based on a standard proposed by a group called the Coalition for Content Provenance and Authenticity (C2PA), which includes Adobe, Microsoft, The New York Times, the BBC, and other media organizations.
The original idea of โโC2PA is based on a camera, like one released by Sony last year, which uses a different type of cryptography to "digitally sign" an image. Once signed, attempts to manipulate or alter the image will be detectable by a viewer running the appropriate software.
The problem with that idea itself is that if the media edits the original photo before publishing the image, the public will no longer be able to validate the digital signature. So Stanford graduate student Trisha Datta and Dan Bonehprofessor of computer science and electrical engineering, suggests that a zero-knowledge proof might be the answer.
Incredibly, the cryptography involved was able to verify that the original raw photo was signed by a C2PA camera and that certain edits occurred. Software running in your browser could check the proof and make sure that the metadata of the photo you see matches the metadata of the raw photo.
As AI-generated content continues to flood our digital spaces and many of those spaces become more hostile, it will become more difficult to determine what is true and who or what to trust. Regardless of what you think about cryptocurrencies, you have given us a powerful tool to decipher such things.
Mike Orcutt is a freelance technology journalist focused on the future of the Internet. He was previously an editor at MIT Technology Review and The Block, a cryptocurrency news publication.
