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Illegal Content and the Blockchain

Security researchers have recently discovered a botnet with a novel defense against takedowns. Normally, authorities can disable a botnet by taking over its command-and-control server. With nowhere to go for instructions, the botnet is rendered useless. But over the years, botnet designers have come up with ways to make this counterattack harder. Now the content-delivery network Akamai has reported on a new method: a botnet that uses the Bitcoin blockchain ledger. Since the blockchain is globally accessible and hard to take down, the botnet’s operators appear to be safe.

It’s best to avoid explaining the mathematics of Bitcoin’s blockchain, but to understand the colossal implications here, you need to understand one concept. Blockchains are a type of “distributed ledger”: a record of all transactions since the beginning, and everyone using the blockchain needs to have access to — and reference — a copy of it. What if someone puts illegal material in the blockchain? Either everyone has a copy of it, or the blockchain’s security fails.

To be fair, not absolutely everyone who uses a blockchain holds a copy of the entire ledger. Many who buy cryptocurrencies like Bitcoin and Ethereum don’t bother using the ledger to verify their purchase. Many don’t actually hold the currency outright, and instead trust an exchange to do the transactions and hold the coins. But people need to continually verify the blockchain’s history on the ledger for the system to be secure. If they stopped, then it would be trivial to forge coins. That’s how the system works.

Some years ago, people started noticing all sorts of things embedded in the Bitcoin blockchain. There are digital images, including one of Nelson Mandela. There’s the Bitcoin logo, and the original paper describing Bitcoin by its alleged founder, the pseudonymous Satoshi Nakamoto. There are advertisements, and several prayers. There’s even illegal pornography and leaked classified documents. All of these were put in by anonymous Bitcoin users. But none of this, so far, appears to seriously threaten those in power in governments and corporations. Once someone adds something to the Bitcoin ledger, it becomes sacrosanct. Removing something requires a fork of the blockchain, in which Bitcoin fragments into multiple parallel cryptocurrencies (and associated blockchains). Forks happen, rarely, but never yet because of legal coercion. And repeated forking would destroy Bitcoin’s stature as a stable(ish) currency.

The botnet’s designers are using this idea to create an unblockable means of coordination, but the implications are much greater. Imagine someone using this idea to evade government censorship. Most Bitcoin mining happens in China. What if someone added a bunch of Chinese-censored Falun Gong texts to the blockchain?<

What if someone added a type of political speech that Singapore routinely censors? Or cartoons that Disney holds the copyright to?

In Bitcoin’s and most other public blockchains there are no central, trusted authorities. Anyone in the world can perform transactions or become a miner. Everyone is equal to the extent that they have the hardware and electricity to perform cryptographic computations.

This openness is also a vulnerability, one that opens the door to asymmetric threats and small-time malicious actors. Anyone can put information in the one and only Bitcoin blockchain. Again, that’s how the system works.

Over the last three decades, the world has witnessed the power of open networks: blockchains, social media, the very web itself. What makes them so powerful is that their value is related not just to the number of users, but the number of potential links between users. This is Metcalfe’s law — value in a network is quadratic, not linear, in the number of users — and every open network since has followed its prophecy.

As Bitcoin has grown, its monetary value has skyrocketed, even if its uses remain unclear. With no barrier to entry, the blockchain space has been a Wild West of innovation and lawlessness. But today, many prominent advocates suggest Bitcoin should become a global, universal currency. In this context, asymmetric threats like embedded illegal data become a major challenge.

The philosophy behind Bitcoin traces to the earliest days of the open internet. Articulated in John Perry Barlow’s 1996 Declaration of the Independence of Cyberspace, it was and is the ethos of tech startups: Code is more trustworthy than institutions. Information is meant to be free, and nobody has the right — and should not have the ability — to control it.

But information must reside somewhere. Code is written by and for people, stored on computers located within countries, and embedded within the institutions and societies we have created. To trust information is to trust its chain of custody and the social context it comes from. Neither code nor information is value-neutral, nor ever free of human context.

Today, Barlow’s vision is a mere shadow; every society controls the information its people can access. Some of this control is through overt censorship, as China controls information about Taiwan, Tiananmen Square, and the Uyghurs. Some of this is through civil laws designed by the powerful for their benefit, as with Disney and US copyright law, or UK libel law.

Bitcoin and blockchains like it are on a collision course with these laws. What happens when the interests of the powerful, with the law on their side, are pitted against an open blockchain? Let’s imagine how our various scenarios might play out.

China first: In response to Falun Gong texts in the blockchain, the People’s Republic decrees that any miners processing blocks with banned content will be taken offline — their IPs will be blacklisted. This causes a hard fork of the blockchain at the point just before the banned content. China might do this under the guise of a “patriotic” messaging campaign, publicly stating that it’s merely maintaining financial sovereignty from Western banks. Then it uses paid influencers and moderators on social media to pump the China Bitcoin fork, through both partisan comments and transactions. Two distinct forks would soon emerge, one behind China’s Great Firewall and one outside. Other countries with similar governmental and media ecosystems — Russia, Singapore, Myanmar — might consider following suit, creating multiple national Bitcoin forks. These would operate independently, under mandates to censor unacceptable transactions from then on.

Disney’s approach would play out differently. Imagine the company announces it will sue any ISP that hosts copyrighted content, starting with networks hosting the biggest miners. (Disney has sued to enforce its intellectual property rights in China before.) After some legal pressure, the networks cut the miners off. The miners reestablish themselves on another network, but Disney keeps the pressure on. Eventually miners get pushed further and further off of mainstream network providers, and resort to tunneling their traffic through an anonymity service like Tor. That causes a major slowdown in the already slow (because of the mathematics) Bitcoin network. Disney might issue takedown requests for Tor exit nodes, causing the network to slow to a crawl. It could persist like this for a long time without a fork. Or the slowdown could cause people to jump ship, either by forking Bitcoin or switching to another cryptocurrency without the copyrighted content.

And then there’s illegal pornographic content and leaked classified data. These have been on the Bitcoin blockchain for over five years, and nothing has been done about it. Just like the botnet example, it may be that these do not threaten existing power structures enough to warrant takedowns. This could easily change if Bitcoin becomes a popular way to share child sexual abuse material. Simply having these illegal images on your hard drive is a felony, which could have significant repercussions for anyone involved in Bitcoin.

Whichever scenario plays out, this may be the Achilles heel of Bitcoin as a global currency.

If an open network such as a blockchain were threatened by a powerful organization — China’s censors, Disney’s lawyers, or the FBI trying to take down a more dangerous botnet — it could fragment into multiple networks. That’s not just a nuisance, but an existential risk to Bitcoin.

Suppose Bitcoin were fragmented into 10 smaller blockchains, perhaps by geography: one in China, another in the US, and so on. These fragments might retain their original users, and by ordinary logic, nothing would have changed. But Metcalfe’s law implies that the overall value of these blockchain fragments combined would be a mere tenth of the original. That is because the value of an open network relates to how many others you can communicate with — and, in a blockchain, transact with. Since the security of bitcoin currency is achieved through expensive computations, fragmented blockchains are also easier to attack in a conventional manner — through a 51 percent attack — by an organized attacker. This is especially the case if the smaller blockchains all use the same hash function, as they would here.

Traditional currencies are generally not vulnerable to these sorts of asymmetric threats. There are no viable small-scale attacks against the US dollar, or almost any other fiat currency. The institutions and beliefs that give money its value are deep-seated, despite instances of currency hyperinflation.

The only notable attacks against fiat currencies are in the form of counterfeiting. Even in the past, when counterfeit bills were common, attacks could be thwarted. Counterfeiters require specialized equipment and are vulnerable to law enforcement discovery and arrest. Furthermore, most money today — even if it’s nominally in a fiat currency — doesn’t exist in paper form.

Bitcoin attracted a following for its openness and immunity from government control. Its goal is to create a world that replaces cultural power with cryptographic power: verification in code, not trust in people. But there is no such world. And today, that feature is a vulnerability. We really don’t know what will happen when the human systems of trust come into conflict with the trustless verification that make blockchain currencies unique. Just last week we saw this exact attack on smaller blockchains — not Bitcoin yet. We are watching a public socio-technical experiment in the making, and we will witness its success or failure in the not-too-distant future.

This essay was written with Barath Raghavan, and previously appeared on Wired.com.

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Voatz Internet Voting App Is Insecure

This paper describes the flaws in the Voatz Internet voting app: “The Ballot is Busted Before the Blockchain: A Security Analysis of Voatz, the First Internet Voting Application Used in U.S. Federal Elections.”

Abstract: In the 2018 midterm elections, West Virginia became the first state in the U.S. to allow select voters to cast their ballot on a mobile phone via a proprietary app called “Voatz.” Although there is no public formal description of Voatz’s security model, the company claims that election security and integrity are maintained through the use of a permissioned blockchain, biometrics, a mixnet, and hardware-backed key storage modules on the user’s device. In this work, we present the first public security analysis of Voatz, based on a reverse engineering of their Android application and the minimal available documentation of the system. We performed a clean-room reimplementation of Voatz’s server and present an analysis of the election process as visible from the app itself.

We find that Voatz has vulnerabilities that allow different kinds of adversaries to alter, stop, or expose a user’s vote,including a sidechannel attack in which a completely passive network adversary can potentially recover a user’s secret ballot. We additionally find that Voatz has a number of privacy issues stemming from their use of third party services for crucial app functionality. Our findings serve as a concrete illustration of the common wisdom against Internet voting,and of the importance of transparency to the legitimacy of elections.

News articles.

The company’s response is a perfect illustration of why non-computer non-security companies have no idea what they’re doing, and should not be trusted with any form of security.

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Chrome Extension Stealing Cryptocurrency Keys and Passwords

A malicious Chrome extension surreptitiously steals Ethereum keys and passwords:

According to Denley, the extension is dangerous to users in two ways. First, any funds (ETH coins and ERC0-based tokens) managed directly inside the extension are at risk.

Denley says that the extension sends the private keys of all wallets created or managed through its interface to a third-party website located at erc20wallet[.]tk.

Second, the extension also actively injects malicious JavaScript code when users navigate to five well-known and popular cryptocurrency management platforms. This code steals login credentials and private keys, data that it’s sent to the same erc20wallet[.]tk third-party website.

Another example of how blockchain requires many single points of trust in order to be secure.

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Presidential Candidate Andrew Yang Has Quantum Encryption Policy

At least one presidential candidate has a policy about quantum computing and encryption.

It has two basic planks. One: fund quantum-resistant encryption standards. (Note: NIST is already doing this.) Two, fund quantum computing. (Unlike many far more pressing computer security problems, the market seems to be doing this on its own quite nicely.)

Okay, so not the greatest policy — but at least one candidate has a policy. Do any of the other candidates have anything else in this area?

Yang has also talked about blockchain: “

“I believe that blockchain needs to be a big part of our future,” Yang told a crowded room at the Consensus conference in New York, where he gave a keynote address Wednesday. “If I’m in the White House, oh boy are we going to have some fun in terms of the crypto currency community.”

Okay, so that’s not so great, either. But again, I don’t think anyone else talks about this.

Note: this is not an invitation to talk more general politics. Not even an invitation to explain how good or bad Andrew Yang’s chances are. Or anyone else’s. Please.

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Blockchain and Trust

In his 2008 white paper that first proposed bitcoin, the anonymous Satoshi Nakamoto concluded with: “We have proposed a system for electronic transactions without relying on trust.” He was referring to blockchain, the system behind bitcoin cryptocurrency. The circumvention of trust is a great promise, but it’s just not true. Yes, bitcoin eliminates certain trusted intermediaries that are inherent in other payment systems like credit cards. But you still have to trust bitcoin — and everything about it.

Much has been written about blockchains and how they displace, reshape, or eliminate trust. But when you analyze both blockchain and trust, you quickly realize that there is much more hype than value. Blockchain solutions are often much worse than what they replace.

First, a caveat. By blockchain, I mean something very specific: the data structures and protocols that make up a public blockchain. These have three essential elements. The first is a distributed (as in multiple copies) but centralized (as in there’s only one) ledger, which is a way of recording what happened and in what order. This ledger is public, meaning that anyone can read it, and immutable, meaning that no one can change what happened in the past.

The second element is the consensus algorithm, which is a way to ensure all the copies of the ledger are the same. This is generally called mining; a critical part of the system is that anyone can participate. It is also distributed, meaning that you don’t have to trust any particular node in the consensus network. It can also be extremely expensive, both in data storage and in the energy required to maintain it. Bitcoin has the most expensive consensus algorithm the world has ever seen, by far.

Finally, the third element is the currency. This is some sort of digital token that has value and is publicly traded. Currency is a necessary element of a blockchain to align the incentives of everyone involved. Transactions involving these tokens are stored on the ledger.

Private blockchains are completely uninteresting. (By this, I mean systems that use the blockchain data structure but don’t have the above three elements.) In general, they have some external limitation on who can interact with the blockchain and its features. These are not anything new; they’re distributed append-only data structures with a list of individuals authorized to add to it. Consensus protocols have been studied in distributed systems for more than 60 years. Append-only data structures have been similarly well covered. They’re blockchains in name only, and — as far as I can tell — the only reason to operate one is to ride on the blockchain hype.

All three elements of a public blockchain fit together as a single network that offers new security properties. The question is: Is it actually good for anything? It’s all a matter of trust.

Trust is essential to society. As a species, humans are wired to trust one another. Society can’t function without trust, and the fact that we mostly don’t even think about it is a measure of how well trust works.

The word “trust” is loaded with many meanings. There’s personal and intimate trust. When we say we trust a friend, we mean that we trust their intentions and know that those intentions will inform their actions. There’s also the less intimate, less personal trust — we might not know someone personally, or know their motivations, but we can trust their future actions. Blockchain enables this sort of trust: We don’t know any bitcoin miners, for example, but we trust that they will follow the mining protocol and make the whole system work.

Most blockchain enthusiasts have a unnaturally narrow definition of trust. They’re fond of catchphrases like “in code we trust,” “in math we trust,” and “in crypto we trust.” This is trust as verification. But verification isn’t the same as trust.

In 2012, I wrote a book about trust and security, Liars and Outliers. In it, I listed four very general systems our species uses to incentivize trustworthy behavior. The first two are morals and reputation. The problem is that they scale only to a certain population size. Primitive systems were good enough for small communities, but larger communities required delegation, and more formalism.

The third is institutions. Institutions have rules and laws that induce people to behave according to the group norm, imposing sanctions on those who do not. In a sense, laws formalize reputation. Finally, the fourth is security systems. These are the wide varieties of security technologies we employ: door locks and tall fences, alarm systems and guards, forensics and audit systems, and so on.

These four elements work together to enable trust. Take banking, for example. Financial institutions, merchants, and individuals are all concerned with their reputations, which prevents theft and fraud. The laws and regulations surrounding every aspect of banking keep everyone in line, including backstops that limit risks in the case of fraud. And there are lots of security systems in place, from anti-counterfeiting technologies to internet-security technologies.

In his 2018 book, Blockchain and the New Architecture of Trust, Kevin Werbach outlines four different “trust architectures.” The first is peer-to-peer trust. This basically corresponds to my morals and reputational systems: pairs of people who come to trust each other. His second is leviathan trust, which corresponds to institutional trust. You can see this working in our system of contracts, which allows parties that don’t trust each other to enter into an agreement because they both trust that a government system will help resolve disputes. His third is intermediary trust. A good example is the credit card system, which allows untrusting buyers and sellers to engage in commerce. His fourth trust architecture is distributed trust. This is emergent trust in the particular security system that is blockchain.

What blockchain does is shift some of the trust in people and institutions to trust in technology. You need to trust the cryptography, the protocols, the software, the computers and the network. And you need to trust them absolutely, because they’re often single points of failure.

When that trust turns out to be misplaced, there is no recourse. If your bitcoin exchange gets hacked, you lose all of your money. If your bitcoin wallet gets hacked, you lose all of your money. If you forget your login credentials, you lose all of your money. If there’s a bug in the code of your smart contract, you lose all of your money. If someone successfully hacks the blockchain security, you lose all of your money. In many ways, trusting technology is harder than trusting people. Would you rather trust a human legal system or the details of some computer code you don’t have the expertise to audit?

Blockchain enthusiasts point to more traditional forms of trust — bank processing fees, for example — as expensive. But blockchain trust is also costly; the cost is just hidden. For bitcoin, that’s the cost of the additional bitcoin mined, the transaction fees, and the enormous environmental waste.

Blockchain doesn’t eliminate the need to trust human institutions. There will always be a big gap that can’t be addressed by technology alone. People still need to be in charge, and there is always a need for governance outside the system. This is obvious in the ongoing debate about changing the bitcoin block size, or in fixing the DAO attack against Ethereum. There’s always a need to override the rules, and there’s always a need for the ability to make permanent rules changes. As long as hard forks are a possibility — that’s when the people in charge of a blockchain step outside the system to change it — people will need to be in charge.

Any blockchain system will have to coexist with other, more conventional systems. Modern banking, for example, is designed to be reversible. Bitcoin is not. That makes it hard to make the two compatible, and the result is often an insecurity. Steve Wozniak was scammed out of $70K in bitcoin because he forgot this.

Blockchain technology is often centralized. Bitcoin might theoretically be based on distributed trust, but in practice, that’s just not true. Just about everyone using bitcoin has to trust one of the few available wallets and use one of the few available exchanges. People have to trust the software and the operating systems and the computers everything is running on. And we’ve seen attacks against wallets and exchanges. We’ve seen Trojans and phishing and password guessing. Criminals have even used flaws in the system that people use to repair their cell phones to steal bitcoin.

Moreover, in any distributed trust system, there are backdoor methods for centralization to creep back in. With bitcoin, there are only a few miners of consequence. There’s one company that provides most of the mining hardware. There are only a few dominant exchanges. To the extent that most people interact with bitcoin, it is through these centralized systems. This also allows for attacks against blockchain-based systems.

These issues are not bugs in current blockchain applications, they’re inherent in how blockchain works. Any evaluation of the security of the system has to take the whole socio-technical system into account. Too many blockchain enthusiasts focus on the technology and ignore the rest.

To the extent that people don’t use bitcoin, it’s because they don’t trust bitcoin. That has nothing to do with the cryptography or the protocols. In fact, a system where you can lose your life savings if you forget your key or download a piece of malware is not particularly trustworthy. No amount of explaining how SHA-256 works to prevent double-spending will fix that.

Similarly, to the extent that people do use blockchains, it is because they trust them. People either own bitcoin or not based on reputation; that’s true even for speculators who own bitcoin simply because they think it will make them rich quickly. People choose a wallet for their cryptocurrency, and an exchange for their transactions, based on reputation. We even evaluate and trust the cryptography that underpins blockchains based on the algorithms’ reputation.

To see how this can fail, look at the various supply-chain security systems that are using blockchain. A blockchain isn’t a necessary feature of any of them. The reasons they’re successful is that everyone has a single software platform to enter their data in. Even though the blockchain systems are built on distributed trust, people don’t necessarily accept that. For example, some companies don’t trust the IBM/Maersk system because it’s not their blockchain.

Irrational? Maybe, but that’s how trust works. It can’t be replaced by algorithms and protocols. It’s much more social than that.

Still, the idea that blockchains can somehow eliminate the need for trust persists. Recently, I received an email from a company that implemented secure messaging using blockchain. It said, in part: “Using the blockchain, as we have done, has eliminated the need for Trust.” This sentiment suggests the writer misunderstands both what blockchain does and how trust works.

Do you need a public blockchain? The answer is almost certainly no. A blockchain probably doesn’t solve the security problems you think it solves. The security problems it solves are probably not the ones you have. (Manipulating audit data is probably not your major security risk.) A false trust in blockchain can itself be a security risk. The inefficiencies, especially in scaling, are probably not worth it. I have looked at many blockchain applications, and all of them could achieve the same security properties without using a blockchain­ — of course, then they wouldn’t have the cool name.

Honestly, cryptocurrencies are useless. They’re only used by speculators looking for quick riches, people who don’t like government-backed currencies, and criminals who want a black-market way to exchange money.

To answer the question of whether the blockchain is needed, ask yourself: Does the blockchain change the system of trust in any meaningful way, or just shift it around? Does it just try to replace trust with verification? Does it strengthen existing trust relationships, or try to go against them? How can trust be abused in the new system, and is this better or worse than the potential abuses in the old system? And lastly: What would your system look like if you didn’t use blockchain at all?

If you ask yourself those questions, it’s likely you’ll choose solutions that don’t use public blockchain. And that’ll be a good thing — especially when the hype dissipates.

This essay previously appeared on Wired.com.

EDITED TO ADD (2/11): Two commentaries on my essay.

I have wanted to write this essay for over a year. The impetus to finally do it came from an invite to speak at the Hyperledger Global Forum in December. This essay is a version of the talk I wrote for that event, made more accessible to a general audience.

It seems to be the season for blockchain takedowns. James Waldo has an excellent essay in Queue. And Nicholas Weaver gave a talk at the Enigma Conference, summarized here. It’s a shortened version of this talk.

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Friday Squid Blogging: Squid Falsely Labeled as Octopus

Two New Yorkers have been charged with importing squid from Peru and then reselling it as octopus.

Yet another problem that a blockchain-enabled supply-chain system won’t solve.

As usual, you can also use this squid post to talk about the security stories in the news that I haven’t covered.

Read my blog posting guidelines here.

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