My quest to solve bitcoin’s great mystery

In the end, I found the conclusion of “Money Electric: The Bitcoin Mystery” unconvincing: HBO singled out a Canadian software developer based on what seemed like very thin evidence. But as I watched what was an otherwise entertaining romp through the world of crypto, one scene caught my attention.

Adam Back, a British cryptographer and leading figure in the bitcoin movement, sat on a park bench in Riga, Latvia, his shirt untucked under a brown coat. The filmmaker casually rattled off the names of several Satoshi suspects. At the mention of his own name, Back tensed up, strenuously denied he was Satoshi and asked that the conversation be kept off the record.

Having encountered my share of liars and developed something of an expertise in their tells, Back’s demeanor — his shifty eyes, his awkward chuckle, the jerky movement of his left hand — struck me as fishy. When the credits rolled up, I replayed the sequence several times on my TV.

While I pondered Back’s reaction, another thought occurred to me. An Australian impostor had been sued for falsely claiming he was Satoshi. What if the evidence disclosed in that court case, which had been tried in London a few months earlier, could help me unravel the mystery?

As anyone steeped in bitcoin lore will tell you, Satoshi was a master at the art of maintaining anonymity on the internet, leaving few, if any, digital footprints behind.

But Satoshi did leave behind a corpus of texts, including a nine-page white paper outlining his invention and his many posts on the Bitcointalk forum, an online message board where users gathered to discuss the digital currency’s software, economics and philosophy. And that corpus, it turned out, had expanded significantly during the impostor’s civil trial when Martti Malmi, a Finnish programmer who collaborated with Satoshi in bitcoin’s early days, released a trove of hundreds of emails he had exchanged with him. Emails Satoshi sent to other early Bitcoin adopters had surfaced before, but none came close in volume to the Malmi dump. If Satoshi was ever going to be found, I was convinced the key lay somewhere in these texts.

Then again, others must have gone down this road before me. Journalists, academics and internet sleuths had been trying to identify Satoshi for 16 years. During that span, more than 100 names had been put forward, including those of an Irish cryptography student, an unemployed Japanese American engineer, a South African criminal mastermind and the mathematician portrayed in the movie “A Beautiful Mind.”

The most alluring theories had focused on coincidences that aligned with what little was known about Satoshi: a particular code-writing style, a mysterious work history, an expertise in bitcoin’s key technical concepts, an anti-government worldview. But they had run aground under the weight of an alibi or some other piece of inconsistent or contrary evidence. Each failure had been met with glee by many members of the bitcoin community. As they liked to point out, only Satoshi could definitively prove his identity by moving some of his coins. Any evidence short of that would be circumstantial.

It seemed foolish to think that I could somehow crack a case that had confounded so many others. But I craved the thrill of a big, challenging story. So I decided to try once more to unmask bitcoin’s mysterious creator.

I. A Series of Clues

Two Thin Leads

I started by looking for ways to narrow the field.

One thing that jumped out in Satoshi’s emails to Malmi and in his other writings was that he mixed British spelling and idioms with American expressions. Since many Satoshi suspects are American, some have speculated that he disguised his prose with Britishisms. But I never bought that theory because of a clue Satoshi left us.

In bitcoin’s first block of transactions, Satoshi embedded text from a newspaper headline: “The Times 03/Jan/2009 Chancellor on brink of second bailout for banks.” The headline in question appeared in The Times of London’s British print edition. This felt like a sign that Satoshi really was British.

Satoshi was also very likely a member of the Cypherpunks, a group of anarchists formed in the early 1990s who wanted to use cryptography, the art of securing communications through code, to free individuals from government surveillance and censorship. The Cypherpunks interacted mostly through something called an internet mailing list. Ancestors of today’s message boards, mailing lists were large group emails in old typewriter font that subscribers received in their inbox. To communicate, respondents replied-all.

It’s hard to picture in the age of Venmo and Apple Pay, but one of the Cypherpunks’ biggest concerns was the digitization of financial transactions. When you hand someone a $20 bill, no one knows where it came from. But when you pay for something with a check or a credit card, banks keep computer records. Cypherpunks worried that governments would use those records to track people’s lives. On their mailing list, they brainstormed about how to create “electronic cash”: digital money that would preserve the anonymity of physical currency. Some even came up with their own electronic cash systems, but none caught on — until bitcoin.

Besides their shared interest in digital cash, there were other indications Satoshi belonged to the group. He announced his white paper on an offshoot of the Cypherpunks mailing list called the Cryptography list, and he seemed familiar with two of the group’s members.

At its peak in the late 1990s, the Cypherpunks counted some 2,000 followers, so that still left a wide pool of candidates.

Armed with these admittedly thin leads, I pored over Satoshi’s body of writing, especially the emails released by Malmi, and made a list of words and phrases that stood out to me. It felt like trying to decipher a foreign dialect. More than once, I wondered whether I was engaging in a useless exercise.

My list eventually grew to more than a hundred words and phrases, taking up several pages in my notebook. Among those that caught my eye: “dang”; “backup,” used as a verb in one word; “human friendly”; “on principle”; “burning the money”; “abandonware”; “hand tuned”; and “partial pre-image.”

One phrase — “a menace to the network” — sounded like a line from a science fiction movie. The rest hinted at a weird combination of upper-class Brit, American redneck, computer geek and cryptographer.

Using the advanced search function on the social media platform X, I did a cursory search to see if any of the dozen or so people most often suspected of being Satoshi used the terms I had highlighted. Not all Satoshi suspects have X accounts, so this wasn’t meant to be scientific. But, just as I had hoped, one person was a match for nearly all of my words and phrases: Back.

Staring at a long column of check marks I’d jotted in my notebook under his name, I felt a rush of adrenaline. My hunch now seemed at least partially founded. Back’s use of many of the same terms as Satoshi might not prove anything to a community that had been consumed with this topic for many years, but I doubted it was just chance.

As I took a closer look at Back, I realized he had several attributes that were consistent with Satoshi. For starters, he was British and he was a Cypherpunk. More important, Back had invented Hashcash, a statistical puzzle-solving system that Satoshi borrowed for the mining of bitcoins. Satoshi had cited Back and Hashcash in his white paper.

But Back had produced emails during the Australian impostor’s trial showing that Satoshi had contacted him in August 2008 before publishing the bitcoin white paper to check his citation of Back’s Hashcash paper. Those emails seemed like proof that Back couldn’t be Satoshi.

As I thought about it, however, I glimpsed a different possibility: Back could just as well have sent those emails to himself as a cover story.

‘Down the Cryptography Rabbit Hole’

With his wire-rimmed glasses, thinning gray hair and goatee, Back, 55, looks like a disheveled mathematician. Over the past dozen years, he has built a mini-empire of bitcoin-related companies and become one of the community’s most influential members.

Back has long been among the top Satoshi candidates. But, unlike some other leading suspects, he hasn’t been the subject of close journalistic scrutiny, other than in a 2020 video by an anonymous YouTuber who goes by the handle “Barely Sociable.”

A year ago, I flew to Las Vegas to meet him. He was scheduled to speak at the Bitcoin2025 conference at the Venetian Resort. I wasn’t sure I had the right person, so I wasn’t planning on confronting him yet. I just wanted to get to know him and learn more about his background. If my reporting bore out, I envisioned cornering him with all of my evidence later in a final, dramatic showdown, like a police detective trying to extract a confession from a murder suspect. But for now, I wanted to put him at ease and establish a rapport.

I approached Back after watching him confidently predict on a panel that bitcoin, then trading around $108,000, would reach “a million easy” in five to 10 years. (Fittingly, conference organizers had christened the stage he spoke on the “Nakamoto Stage.”) He seemed slightly startled even though I had arranged an interview ahead of time.

I told Back only that I was working on a story about the history of bitcoin, but he may have suspected what I was really up to because I had already contacted six former colleagues from three companies he had been involved with. If he did, he didn’t show it. He was patient and friendly. It was hard to fathom that this soft-spoken, middle-aged nerd who took no visible security precautions might be one of the world’s richest people. According to bitcoin lore, Satoshi had mined 1.1 million coins in the digital currency’s early days, a hoard worth $118 billion at the time of the conference.

I found Back talkative when it came to bitcoin but more reticent when I shifted the conversation to his early life. I eventually elicited the following from him: He was born in London in 1970. His father was an entrepreneur and his mother was a legal secretary. They moved around a lot, and family members had strong opinions and weren’t shy about voicing them.

Back said he taught himself how to code on a Timex Sinclair personal computer at age 11 and took interest in cryptography in high school. That became a passion at the University of Exeter when a fellow student turned Back, who was pursuing a doctorate in computer science, onto PGP, a free encryption program used by anti-nuclear activists and human rights groups to shield their files and emails from government surveillance.

Back was so taken with the many potential applications of PGP, which stands for Pretty Good Privacy, that he said he spent most of his Ph.D. “diving down the cryptography rabbit hole.” He got so sidetracked, he recalled, that he had to cram his thesis into his last six months at the university, comparing himself to a pilot crash-landing a plane.

I’d learned enough by then to know that PGP relies on public-key cryptography.

So does bitcoin. A bitcoin user has two keys: a public key, from which an address is derived that acts as a digital safe deposit box; and a private key, which is the secret combination used to unlock that box and spend the coins it contains.

How interesting, I thought, that Back’s grad-school hobby involved the same cryptographic technique that Satoshi had repurposed.

The topic of Back’s doctoral thesis, he told me, was distributed computer systems: Programs that rely on a web of independent computers known in computer parlance as “nodes” to work together to run their software. This was another technological pillar of bitcoin.

And Back’s thesis project focused on C++ — the same programming language Satoshi used to code the first version of the bitcoin software.

After nearly two hours, Back politely signaled that he had other commitments that evening, so we cordially parted ways. I told him I would be in touch if I had other questions.

Becoming a Cypherpunk

Before my trip to Las Vegas, I had begun to immerse myself in the archives of the Cypherpunks mailing list to learn more about the strange underground world that had produced Satoshi. When I returned to New York, I plunged back in.

Unlike a social-media platform like Facebook, the Cypherpunks list was a decentralized communication forum. Privacy-minded cryptography geeks gathered there to bat around subversive ideas without fear of being censored. In the process, they planted the seeds for innovations that would change the course of financial history.

Their messages were preserved for posterity on several obscure websites. One of them greeted me with a skull-and-crossbones logo and the slogan, “Arise, you have nothing to lose but your barbed wire fences!” I found myself staring at thousands of emails dense with cryptospeak I barely grasped.

Back joined the list in the summer of 1995, toward the end of his graduate studies. He quickly became a vocal participant, churning out posts on topics ranging from digital privacy to his miserly spending habits.

In one of his first posts, he solved a cryptographic challenge, a sort of mathematical riddle, posted by Hal Finney, a Cypherpunk from California who had worked on PGP. It marked the beginning of an online friendship: Decades later, Back tweeted that he and Finney had interacted numerous times on and off the list and he admired Finney’s focus and coding chops.

Satoshi, too, was friendly with Finney. When Satoshi unveiled his white paper, Finney complimented it. Later, Finney volunteered to receive some bitcoins in what became the world’s first bitcoin transaction. There was no evidence that Finney knew who Satoshi was, but one of their interactions suggested Satoshi was familiar with Finney.

In December 2010, Finney wrote a post on Bitcointalk praising the bitcoin code. Two hours later, Satoshi responded, “That means a lot coming from you, Hal.”

There was something else that made me think Satoshi and Finney shared a history. In one of his emails to Malmi, Satoshi made a reference to an electronic cash system Finney had invented called Reusable Proofs of Work.

Like bitcoin, RPOW incorporated Hashcash into its design but, unlike bitcoin, it had attracted virtually no interest from the cryptographic community. Only a handful of people had commented on it on the Cypherpunks and Cryptography lists.

One of the few who had was Back.

A Gold Nugget

In the Cypherpunks, Back had found his ideological soulmates. I pictured him in his home in London logging onto the internet with a dial-up modem after work and whiling the nights away in philosophical arguments with other group members half a world away.

Like many of his new pen pals, Back embraced “crypto anarchy,” an ideology that essentially meant using cryptography to shield individuals’ lives from state encroachment.

As a Libertarian, Back was incensed when the Clinton administration opened a criminal investigation into PGPs founder. At the time, the U.S. government considered encryption programs vital to national security and believed that the release of PGP’s source code online was tantamount to exporting banned munitions.

In protest, Back made T-shirts with a strong encryption algorithm printed on them and mailed them to Cypherpunks in other countries. His point was that the U.S. ban on the export of sensitive cryptography violated free-speech principles and couldn’t be enforced.

As I delighted in the cleverness of Back’s prank, it dawned on me that Satoshi, too, had used code to send political messages. Satoshi had likely embedded that Times of London headline in the first block of transactions in part to decry the British government’s bank bailouts during the financial crisis, which was raging at the time.

Satoshi had planted another political message on a website popular with fans of decentralized technologies. He claimed that his date of birth was April 5, 1975. April 5 was the day in 1933 when President Franklin D. Roosevelt had banned the private ownership of gold to allow the government to devalue the dollar during the Great Depression, and 1975 was the year the ban had ended.

Financial commentator Dominic Frisby had spotted this Easter egg more than a decade ago and recognized its meaning: Bitcoin was a digital version of gold that the state could neither outlaw nor devalue.

But no one seemed to have noticed this short post from Back in 2002:

“Just curious, but what was the rationale under which private possession of gold was made illegal in the US? It boggles the mind …”

Spam on the Brain

As I chewed on this odd coincidence, I noticed something else Satoshi and Back had in common: a weird preoccupation with spam.

Among his various Cypherpunk hobbies, Back ran a remailer, a service that enabled its users to communicate anonymously by stripping identifying data from their emails before forwarding them on. To his great annoyance, spammers took advantage of it to bombard people with garbage.

Back invented Hashcash in March 1997 as a way to fight back. The idea was to impose a postage fee on every email sent through his remailer. The postage fees were paid in Hashcash, which users generated by solving little mathematical problems requiring lots of calculations. The math problems took a computer only a few seconds to solve, but they imposed a costly computer-resource burden on spammers who were sending hundreds of thousands of emails at a time.

While reading through the Satoshi corpus a second and then a third time, I began seeing the word “spam” everywhere. By my count, Satoshi mentioned it 24 times, and he often expressed ideas identical to Back’s.

Five months after unveiling Hashcash, Back suggested on the Cypherpunks list that his invention could be useful to celebrities as a way to filter their emails. In a January 2009 post to the Cryptography list, Satoshi proposed a similar use for bitcoin.

It wasn’t an obvious use case for Satoshi’s new electronic money unless filtering junk email was on your brain, as it had been on Back’s for more than a decade.

Satoshi also believed that bitcoin could lead to an overall reduction in spam. Days after releasing his white paper, he argued that his creation might give the armies of zombie computers commandeered by hackers to flood email inboxes a new purpose: “generating bitcoins instead.”

His argument didn’t gain any traction and spam continued to proliferate. Yet Back would make the very same point on Bitcointalk four years later: “Maybe spam would even fall if Hashcash CPU/GPU mining is a more profitable market than spamming. It seems to me highly likely that it would be,” he wrote.

Mr. Average

I was having less luck finding cracks in Satoshi’s deep cover that might lead to a true smoking gun. Conventional wisdom was that he had made two mistakes. The first one involved a leaked IP address that appeared to place him in Southern California when he launched the bitcoin software. The other involved a hack of one of his email addresses. After weeks pursuing both leads, I concluded that not only were they dead ends, they probably weren’t mistakes in the first place. How was I going to find someone so good at hiding his tracks?

As I wrestled with this question, it occurred to me that Back, too, was adept at operating anonymously on the internet. Deeply paranoid about government monitoring, he constantly gamed out ways to elude it. In fact, like Satoshi, Back was a big fan of using pseudonyms.

“You must be below the radar belt, you must be essentially invisible to the government, the spooks dossier on you must read Mr Average and be entirely wholesome. Then you must have one or more alter-egos, for your real interests,” he wrote in January 1998.

Satoshi’s chosen alter ego was from Japan. As it happened, Back had expressed interest in the country in 1997, when a Japanese Cypherpunk posted to the list about the creation of Japan’s first remailer.

“Congrats on starting a remailer in a new jurisdiction!” Back responded. “Jurisdiction shopping is good, too — wonder what Japan offers as a jurisdiction opportunity — are there things legal in Japan which are not legal in Europe, or US?”

The Japanese Cypherpunk didn’t answer. But that wouldn’t have prevented Back from later conducting a little research on his own. If he did, he might have come across a company with a Tokyo address called Anonymousspeech LLC that offered anonymous email and web hosting. Satoshi used its services to register the bitcoin.org website and to create two untraceable email accounts.

In 1999, Back moved to Montreal to take a job with a startup that specialized in privacy software. There, he helped build a privacy system called the Freedom Network that allowed its users to browse the internet anonymously. It was a precursor to the Onion Router, a network better known by its acronym, Tor, that anonymizes internet traffic. There is widespread consensus in the bitcoin community that Satoshi used Tor to hide his footprints.

Like bitcoin, the Freedom Network was a distributed computer system. Back and his colleagues tried to make it impervious to government and corporate monitoring.

That was another trait he shared with Satoshi, whose Bitcointalk posts displayed a deep knowledge of network security and how to guard against vulnerabilities. The bitcoin network is widely admired for how well it has withstood hacking attempts.

Napster vs. Gnutella

After several months in the depths of the Cypherpunks list archives, I sometimes lost track of where I was in my research and followed false leads down bizarre cul-de-sacs. While responding to one of the first criticisms of his white paper on the Cryptography list, Satoshi had written: “I didn’t really make that statement as strong as I could have.” I thought I had seen that phrase before and spent several evenings wading through hundreds of 1990s mailing-list posts I’d already read. It soon became clear I had imagined it.

But my rereading wasn’t all in vain. Other parallels between Back and Satoshi started to become apparent. For instance, Back and Satoshi shared a dislike for copyright.

“Scrap patents and copyright,” Back wrote in September 1997.

In keeping with this belief, Back made his Hashcash spam-throttling software open source.

Satoshi did a similar thing. He released the bitcoin software under the Massachusetts Institute of Technology’s open-source license, which allowed anyone to use, modify and distribute it without restrictions.

In the spirit of building something in the public domain, Back and Satoshi also both created internet mailing lists dedicated to their creations — the Hashcash list and the bitcoin-dev list — where they posted software updates listing new features and bug fixes in a format and style that looked strikingly similar.

Satoshi’s Back-like bias against copyright surfaced in other ways. He expressly waived copyright when he shared images of a bitcoin logo he had designed on Bitcointalk, and he encouraged people who wanted to improve upon it to “make their graphics public domain.”

In the early 2000s, copyright enforcement became mainstream news when the popular file-sharing service Napster shut down after being sued by the big music companies. Napster was what’s known as peer-to-peer software, where users share content with one another directly, eliminating the need for a corporate middleman.

Back was appalled. He shared with the Cypherpunks list a paper written by an intellectual property lawyer that detailed all the legal threats that makers of peer-to-peer software now faced.

“My conclusion after reading this,” Back wrote, “is that the safest and simplest thing to do is to just publish such software anonymously.”

Bitcoin, like Napster, was peer-to-peer software. Substitute the government for the music industry and a similar scenario could unfold. If its creator’s identity became known, government lawyers would know whom to go after. If it stayed concealed, there would be no one to sue. If Back and Satoshi were the same person, that would help explain why Satoshi chose to hide.

The music companies were protecting their business interests. The government would have had a different agenda — protecting its monopoly over money.

Like Back, Satoshi considered Napster’s demise a cautionary tale.

Satoshi Nakamoto: Governments are good at cutting off the heads of a centrally controlled networks like Napster, but pure P2P networks like Gnutella and Tor seem to be holding their own.

He was alluding to the fact that, even though its users exchanged songs directly, Napster still used a central server to keep a list of who had what songs. By contrast, Gnutella, another file-sharing service, ran on a network of independent computers spread out all over the world, just like bitcoin.

This made for yet another fascinating coincidence. In a May 2000 post, Back had drawn the exact same comparison between Napster and Gnutella:

Adam Back: Gnutella stands a much better chance of success because Napster servers being central can be closed down. Gnutella basically can’t be shutdown.

Back hadn’t made this comparison just once. He had made it three separate times on the Cypherpunks list.

II. Buried Road Map

Outlining Bitcoin a Decade Before Bitcoin

All these similarities were intriguing, but I didn’t have anything that tied Back directly to the creation of bitcoin. That changed when I discovered a cluster of Cypherpunks posts Back had written between 1997 and 1999, a decade before bitcoin was launched.

On April 30, 1997, he suggested creating an electronic cash system “entirely disconnected” from modern banking that would have four key attributes: It would preserve the privacy of both payer and payee; it would be distributed across a network of computers to make it hard to shut down; it would have some built-in scarcity to prevent excessive inflation; and it wouldn’t require trust in any individual or bank. To achieve the latter, he suggested a fifth component two days later: a publicly verifiable protocol.

All five of these elements later became core to bitcoin.

Four months later, Back returned to the topic of electronic cash, introducing a new feature rooted in game theory.

“An application I have put a bit of thought into is the idea of creating a distributed banking system,” he wrote. “Ideally it is a system where all nodes are equivalent, and k of n of those nodes have to collude before they can compromise the operation of the bank.”

Back was alluding to the Byzantine Generals Problem, a computer science problem that bedevils decentralized systems. In the analogy, “n” number of generals surround an enemy city at war with Byzantium. To invade successfully, they must all agree to attack at the same time, but a subset of “k” generals may be traitors and sabotage the plan. This is also true of distributed computer networks: They can be sabotaged by malicious participants, or nodes, in the network.

Back wanted to create an electronic cash network with so many nodes in so many different places that no one in the mood to sabotage it would be able to find enough conspirators.

That sounded a lot like the system Satoshi described in his white paper 11 years later: Bitcoin would work, Satoshi wrote, “as long as a majority of CPU power is controlled by nodes that are not cooperating to attack the network.”

In his 1997 Cypherpunks list post, Back wrote of nodes that could “come and go” without affecting the network’s operations. In his white paper, Satoshi wrote that nodes could “leave and rejoin the network at will.”

The phrasing was slightly different, but it didn’t require a crack cryptographer to see that Back and Satoshi had proposed the exact same concepts.

On Dec. 6, 1998, Back returned once more to the topic of electronic cash after another Cypherpunk, Wei Dai, floated his own idea, called b-money. As the YouTuber Barely Sociable pointed out in his 2020 video, Back seized on Dai’s proposal.

B-money used public-key cryptography to anonymize users’ accounts, preserving the privacy of payer and payee as Back had envisioned. And it had another feature Back liked.

One problem that confronts anyone trying to create a digital currency is how to mint coins. Dai proposed a system in which users who solved a computational problem would be rewarded with newly minted b-money coins.

Back’s Hashcash invention did something very similar: It rewarded users who solved computational problems with permission to send emails. He suggested repurposing Hashcash and making it the mechanism to mint Dai’s electronic coins.

This was significant because Satoshi had cited Dai in his white paper and later described bitcoin as “an implementation of Wei Dai’s b-money proposal.”

When I stopped to think about it, it was uncanny: Just like Back proposed to do in 1998, Satoshi combined the Hashcash and b-money concepts to create bitcoin. What were the chances of that?

That wasn’t all. In the comments he made about b-money in December 1998, Back anticipated Satoshi’s inflation solution.

Any electronic coin minted by solving computational problems was bound to suffer from runaway inflation because, as computer chips got more powerful, it would become easier for computers to solve the problems and mint new coins. To get around this issue, Back suggested that minting a b-money coin should “require more computational effort over time.”

That’s exactly how Satoshi designed the bitcoin software. He programmed it so that each new block of bitcoin transactions would take an average of 10 minutes to mine and created an algorithm that increased the problem-solving difficulty when faster computer chips began to shrink that time interval.

As if all these prescient insights were not enough, Back proposed another crucial concept in April 1999. For distributed electronic cash to work, there needed to be a public, immutable time stamp of every transaction. Otherwise, a user could spend one coin twice, sending the whole system into chaos.

Back’s solution involved using hash trees — which condense large amounts of data into a single digital fingerprint — and publishing those fingerprints in New York Times classified ads.

Satoshi used the same idea for bitcoin but replaced the classified ads component with Back’s Hashcash, which time-stamped transactions by making the intensive computations used to package them into blocks too expensive and time-consuming to forge.

Back even foreshadowed Satoshi’s response to one of the main criticisms later levied against bitcoin: its heavy electricity use.

He argued in 1998 and 1999 that the energy burned by a combination of Hashcash and b-money would probably be less than what the banking system consumed. When an early reader of the bitcoin white paper raised the issue a decade later, Satoshi made a similar argument.

In short, Back envisioned nearly every facet of bitcoin — and used the same rationalization as Satoshi to excuse its main flaw — a decade before bitcoin was created.

Radio Silence

A month after our meeting in Vegas, I emailed Back some questions about his work history, and about why he had moved to Malta in 2009. I didn’t say why I was asking, but some members of the bitcoin community had pointed out that the European tax haven would make an ideal home for Satoshi and his trove of bitcoins.

Back replied the next day — politely, but seemingly with a firm grasp of the implication of my question. He moved to Malta for several reasons, including cost of living, weather and, yes, taxes, he wrote. “Bitcoiners love sleuthing but coincidences do happen and don’t necessarily mean anything.”

He clearly knew what I was up to. It was time to test the waters further by broaching something that had been bothering me.

Satoshi had cited both Hashcash and b-money in his white paper. But the emails Back produced for the trial of Craig Wright, the Australian impostor, made it seem like Satoshi wasn’t yet aware of b-money as of August 2008, when he reached out to Back to check whether he was citing his Hashcash paper correctly. It was only after Back referred him to Dai’s website that Satoshi added the b-money citation to his white paper, the emails suggested.

But it didn’t add up to me. Back’s Hashcash paper specifically discussed b-money as an application for Hashcash. Presuming Satoshi read the paper he was planning to cite, he would have had to know about b-money.

Back acknowledged this contradiction in 2020. After he suggested on X that Satoshi might be an anonymous Cypherpunk who had posted about electronic cash, another user questioned his theory, noting that the anonymous Cypherpunk had mentioned b-money and that Satoshi had only learned about b-money many years later, from Back.

Yes, Back responded, but Satoshi could have lied to him and pretended not to know about b-money. “if Satoshi knew some very obscure citation (web page posted on cypherpunks as part of ecash discussion) maybe he would not cite it to avoid triangulation?” he wrote.

Someone like Back, who was one of only six named users to have discussed b-money on the Cypherpunks and Cryptography lists and who had mentioned it no fewer than 60 times, might especially want to avoid this sort of triangulation.

The more I had mulled it over, the more suspicious I had become that Back had written the Satoshi emails to himself in an elaborate ruse to divert suspicion away from himself.

So I decided to ask Back for the emails’ metadata. Metadata is to an email what an envelope, postmark and seal are to a physical letter: It shows where the email came from, when it was sent and whether it was altered. The copies of Back’s email exchanges with Satoshi made public during Wright’s London trial hadn’t included this information.

I didn’t have high hopes the metadata would tell me anything useful because Satoshi had used the Tokyo-registered anonymous email service, which would have masked his IP address. Not only that, Satoshi had probably used Tor to connect to the service to further insulate himself. I still wanted to see it, though, on the off chance I could glean some clue.

But when I emailed Back my request, he did not reply. I wasn’t sure if he was ghosting me or just busy and I didn’t want to spook him by immediately following up, so I waited eight days to send him another email. Again, radio silence.

I had clearly touched a nerve. But why? With the precautions Satoshi had taken, what was there to even hide? Unless Satoshi had made some sort of mistake?

Satoshi Appears, Back Disappears

After unveiling bitcoin on Halloween 2008, Satoshi spent the next 2 1/2 years improving it with the help of a clutch of early enthusiasts who lent their software engineering expertise to the project. Satoshi frequently coordinated with the group, which later became known as the Bitcoin Core developers, on Bitcointalk and by email. Then, famously, he disappeared on April 26, 2011.

Back, it turned out, followed that same pattern — but in reverse.

For more than a decade, whenever electronic money was discussed on the Cypherpunks or the Cryptography list, Back had almost always chimed in, often with long, detailed posts. But when bitcoin, the closest manifestation of the vision he had laid out, arrived, Back was nowhere to be found.

Years later, in December 2013, he gave a very different version of events on the “Let’s Talk Bitcoin” podcast. Back told its host that he had been “very interested technically” in Satoshi’s invention when it came out and had “participated” in the discussion it sparked on the Cryptography list.

I combed through the list for any trace of such participation in the fall of 2008 and the winter of 2009 and found no evidence of it. In fact, Back continued to ignore bitcoin entirely until June 2011, when he made his first public comment about it. That was six weeks after Satoshi vanished.

This vocal advocate of electronic cash who had floated ideas nearly identical to bitcoin showed little to no interest in it for years.

But when he finally did get fully involved, it coincided with a new development that was sure to get Satoshi’s attention. On April 17, 2013, an Argentine cryptographer named Sergio Demian Lerner published a blog item revealing Satoshi’s fortune. That very day, Back joined Bitcointalk.

After Lerner published a follow-up blog post a week later, Back wrote in the comments section: “I suppose if it seems to you that you’re getting too close you might want to stop in Nakamoto’s interests…”

Suddenly All In

Suddenly, Back was all in. Within hours of introducing himself on Bitcointalk, he was proposing complicated system improvements. Within two weeks, he was demanding that Wikipedia restore its stand-alone Satoshi Nakamoto page, which had been deleted and merged into the bitcoin page. And within 18 months, he had founded a startup called Blockstream to build tools that would make the bitcoin network easier to use, faster and more private.

It was the beginning of an era in which Back quickly amassed influence and became a ring leader in the still-small bitcoin community. To staff Blockstream, he poached the top Bitcoin Core developers from their day jobs at companies like Google and Mozilla, giving him tremendous sway over the digital currency. He also became very wealthy: Over the next dozen years, Blockstream and its affiliates would raise $1 billion in funding and Blockstream would reach a valuation of $3.2 billion.

It all seemed consistent with what Satoshi might do if he decided to reappear under the cover of his real name and take back the reins of his creation.

In the fall of 2014, Back and his Blockstream colleagues published a white paper about an innovation Back had conceived called “pegged sidechains.”

The paper, on which Back was the lead author, mentioned DigiCash. Founded by cryptographer David Chaum in the late 1980s, DigiCash created a pioneering electronic currency that, unlike bitcoin, relied on a central server it owned and operated. When DigiCash went bust in 1998, the currency went down with it.

“The requirement for a central server became the Achilles’ heel of” DigiCash, the paper’s introduction said.

That was exactly how Satoshi had described DigiCash’s failings five years earlier: “Of course, the biggest difference is the lack of a central server. That was the Achilles heel of Chaumian systems,” Satoshi wrote.

The following year, in 2015, the bitcoin community fractured over a proposal to increase bitcoin’s block size. A faction led by two bitcoin developers, Gavin Andresen and Mike Hearn, wanted to make the blocks much bigger to accommodate more transactions. But this was controversial because bigger blocks would require users who ran bitcoin nodes to have more powerful hardware and faster internet connections. If the cost of running a node became too high, users would be forced to shut them down, leaving the network in the hands of a few large data centers. That, in turn, would threaten the network’s security because the data centers could collude to take it over.

Back fiercely opposed increasing the block size. In a series of posts on the bitcoin-dev list, he warned against Andresen and Hearn’s proposal in increasingly strident tones.

Then, out of the blue, Satoshi appeared on the list with an email that neatly dovetailed with Back’s position. It was the first time Satoshi had been heard from in more than four years, other than a five-word post the previous year denying a Newsweek article’s claim to have unmasked him.

Many in the bitcoin community questioned the new email’s authenticity since another of Satoshi’s email accounts had been hacked. But Back argued that the email sounded real. In a series of tweets, he called Satoshi’s observations “spot on” and “consistent with Satoshi views IMO” and took to quoting from the email.

Back was likely correct: To this day, there is no evidence to indicate the email was a forgery, and no other emails from that account have surfaced.

The Satoshi email sounded a lot like Back had in his posts during the preceding weeks, although no one took notice. Like Back, Satoshi argued that the bitcoin network’s increasing centralization jeopardized its security. He called the big block proposal very “dangerous” — the same term Back had used repeatedly. He also used other words and phrases Back had used: “widespread consensus,” “consensus rules,” “technical,” “trivial” and “robust.”

At the end of the email, Satoshi denounced Andresen and Hearn as two reckless developers trying to hijack bitcoin with populist tactics and added: “This present situation has been very disappointing to watch unfold.”

Four days later, in the middle of a post to the same thread, Back wrote: “Very disappointing Gavin and Mike.”

III. Closing In

Alternative Theories

I needed to stress test my theory. Late at night in bed or in the shower first thing in the morning, I tried to think of reasons I might be wrong. One argument I’d read in the book “The Mysterious Mr. Nakamoto,” about journalist Benjamin Wallace’s long, inconclusive search for Satoshi, was that Back was a privacy absolutist and bitcoin’s privacy features were weak.

That seemed compelling at first blush. But rather than write bitcoin off like other pro-privacy Cypherpunks, Back had spent the past decade at Blockstream pioneering innovations to strengthen bitcoin’s privacy, which I felt weakened that argument considerably.

On X, Back has cited another argument for why he can’t be Satoshi: He asked too many dumb questions on the #bitcoin-wizards Internet Relay Chat channel when he first joined the community.

The #bitcoin-wizards IRC channel is an internet chat room where the Bitcoin Core developers, or “wizards,” brainstormed about fixing bugs and improving the software.

I read through the channel’s logs and saw little evidence of a clueless beginner. If anything, I was struck by how attuned Back was to bitcoin’s vulnerabilities and how focused he was on shoring them up within weeks of getting involved. Some of his ideas to improve the system were so sophisticated that they flew over the heads of the other wizards.

I also noticed that he was cuttingly dismissive of other cryptocurrencies, writing at one point that he wanted to kill them all.

What about other leading Satoshi suspects, I wondered? Were there any who fit the Satoshi profile better than Back? A 2015 article in this newspaper put forward the thesis that Satoshi was Nick Szabo, an American computer scientist of Hungarian descent who proposed a bitcoin-like idea called “bit gold” in 1998. Szabo remained at the top of many people’s lists until recently, but a heated debate that played out on X about a proposed update to the Bitcoin Core software exposed his ignorance of basic technical aspects of bitcoin.

Finney and Len Sassaman, a software engineer and privacy advocate, were two other oft-cited suspects.

One problem with the Finney hypothesis, however, was that he was photographed running a 10-mile race in April 2009 at the same time as Satoshi was sending emails and bitcoins to someone else. A bigger problem was that Finney and Sassaman were both dead when Satoshi made his final appearance in August 2015. Finney died of ALS in 2014 and Sassaman died by suicide in 2011.

As for HBO’s pick, Peter Todd, the crux of the documentary’s evidence was a 2010 Bitcointalk thread in which Todd corrected Satoshi on a technical point. The film speculated that Todd’s post was actually Satoshi finishing his own thought. This required us to believe that Satoshi, the master of internet operational security, had made the most basic blunder imaginable: accidentally logging in under his real name.

There was also the fact that Todd would have been just 23 when the bitcoin white paper was published, which is very young to solve a challenge that had eluded many older and more experienced cryptographers. Moreover, after the documentary aired, Todd showed Wired magazine photos of himself skiing or spelunking on days and at times when Satoshi was writing on Bitcointalk.

Some have speculated that bitcoin wasn’t created by one person but by a group of individuals. I didn’t buy that theory, either. The more people you let in on a secret, the likelier it is to leak. Satoshi’s secret had remained airtight for 17 years.

‘Better With Code Than With Words’

Back still stood out to me as the likeliest candidate. But by now, that didn’t feel good enough. I went searching for more forensic evidence.

Browsing the Cypherpunks archive one day, I noticed a resemblance that made me nearly jump out of my chair.

When Satoshi had suggested to Finney that Libertarians would embrace bitcoin if they could explain it properly, he had added: I’m better with code than with words though.

Back had expressed the same sentiment in similar language while debating another Cypherpunk about anonymity and free speech: Personally I think I’m better at coding, than constructing convincing arguments.

The closer I looked, the more writing similarities I spotted.

Like Satoshi, Back used two spaces between sentences, an outdated practice that suggests Satoshi is older than 50. Back is 55.

Satoshi had famously used the British expletive “bloody” on Bitcointalk while complaining of how hard it was to explain his invention to a general audience. In several posts on X in October 2023, Back insisted that he had never used that term: “try google and see for yourself not a word i use.”

But I found a 1998 Cypherpunks list post in which Back used “bloody” to express his growing irritation with internet banner ads: “it is getting ridiculus (sic) most of the bandwidth through my trusty 28.8k modem is bloody banners these days!”

Why deny using a word he had in fact used so adamantly if he had nothing to hide?

The most reliable way to identify writers is stylometry, which measures the frequency of, and distance between, function words like “the,” “and,” “of” and “to” to establish an author’s stylistic fingerprint.

In 2022, Florian Cafiero, a computational linguist at France’s École nationale des chartes, used the technique to help The New York Times identify the two people behind the QAnon movement. But Cafiero had tried and failed to identify Satoshi for Wallace’s book.

Thinking he might have missed something, I asked Cafiero to try again and he agreed.

Back was among the suspects Cafiero had considered the first time. But his analysis had been hampered by the fact that most of Back’s papers were coauthored with other cryptographers, which made it difficult to know who really wrote them. This time, Cafiero discarded the joint papers and selected only Back’s Hashcash paper and his Ph.D. thesis. He then added them to a pool of academic papers written by 11 other Satoshi suspects, including Finney, Szabo, Sassaman and Todd.

Cafiero was busy with his teaching job and other projects, so it took about six weeks before he had an answer for me. Every few days, I would ping him over the Signal app to check if he’d made any progress. I tried to temper my expectations but my excitement was mounting.

The verdict arrived by text one morning in late July: After comparing papers from the 12 suspects to the bitcoin white paper, Cafiero’s stylometry program showed Back as the closest match. But he said it wasn’t a snug fit and that Finney was a very close second. In fact, the difference between them was barely distinguishable, he said, and he considered the overall result inconclusive.

I stared at my phone screen in disbelief. It was as though someone had placed a chocolate mousse in front of me and then yanked it away before I could even taste it.

Sensing my frustration, Cafiero changed the way he computed the distance between the 12 suspects’ texts and Satoshi’s white paper. The result was the opposite of what I’d hoped: Other candidates pulled ahead of Back. Cafiero said he considered these results inconclusive too.

After eight months of reporting and countless hours obsessing over Satoshi’s identity, I had thought I was close to solving the mystery. But now it seemed out of reach again.

Spelling and Grammar

For all my disappointment, I had a pretty good idea what the problem was. Cafiero had told me several times that if Satoshi knew how stylometry worked, it would have been easy for him to alter his writing style to guard against it.

It didn’t escape my attention that in a 2020 tweet, Back had described Satoshi’s writing as “concise and focussed” and speculated that he had minimized “emotive flourishes, extraneous adjectives and off topic chit-chat to reduce stylometry risk.” Satoshi and Back both clearly knew a thing or two about stylometry.

In fact, Back had spent a lot of time pondering how to defeat writing analysis.

“I have been thinking about this problem on and off,” he wrote in the fall of 1998, noting that writers using pseudonyms were particularly vulnerable to being identified if they had written prolifically under their real names. He proposed building a multiple-choice sentence constructor with a drop-down menu of nouns, verbs and adjectives that would make it harder to spot a writer’s idiosyncrasies.

With that in mind, I tried a different approach focused on spelling and grammar. Back made a lot of typos and had a rambling style when he posted to mailing lists, while Satoshi’s writing was crisp and mostly typo-free. But, after reading Satoshi’s entire known corpus several times and slogging through more than a thousand of Back’s mailing-list posts, I had detected some writing tics they nonetheless shared.

Back often confused “it’s” and “its,” and he had a habit of putting “also” at the end of sentences. There were five instances of each in Satoshi’s own writing.

Both also seemed pathologically incapable of using hyphens correctly. Like Back, Satoshi tended to add hyphens when they were unnecessary and to omit them when they were needed. For example, he wrote the compound noun “double-spending” with a hyphen but the compound adjectives “hand tuned,” “full blown,” “would be” and “file sharing” without hyphens — just like Back.

Satoshi and Back both tended not to hyphenate compound adjectives that combined a noun with “based,” such as in this Satoshi quote: “In the mint based model, the mint was aware of all transactions and decided which arrived first.”

They both sometimes hyphenated certain words and phrases and sometimes not. For instance, they both alternated between “e-mail” and “email,” “built-in” and “built in,” “off-line” and “offline,” “pre-compiled” and “precompiled” and “to-do list” and “to do list.” Both sometimes spelled out “electronic cash” and sometimes shortened it to “e-cash.”

Like Back, Satoshi alternated between the British “cheque” and the American “check” and the British and American forms of the word “optimize.” And they both sometimes wrote “backup” and “bugfix” as one word instead of two (while using the former as a verb) and “half way” and “down side” as two words instead of one.

When I ran these quirks by Robert Leonard, a forensic linguistics expert at Hofstra University, he said they were exactly the sort of thing he homed in on when trying to identify an author. He called them “markers of sociolinguistic variation” — linguistic fingerprints that could help pinpoint an author’s social background, geographical origin or occupational training. The most revealing were the ones that were common to only a small number of individuals or unique to a particular author, he said. I found at least three in the Satoshi corpus that fit that description.

The first two were cryptographic concepts that Satoshi spelled a particular way. One of them was “proof of work,” which was coined by two cryptographers in a 1999 paper to describe puzzle-solving protocols like Hashcash. Hewing to correct grammar, the authors did not hyphenate the term since it was a compound noun.

But Satoshi did. In his bitcoin white paper, he repeatedly wrote “proof-of-work” with hyphens. Until that point, only eight people had hyphenated it on the Cypherpunks or Cryptography lists when using it as a compound noun.

Looking for ways to narrow down that list of eight names, I remembered that Satoshi had mentioned an obscure Russian online currency called WebMoney in one of his emails to Malmi. After some digging, I had determined that only four people had ever mentioned WebMoney on the Cypherpunks or Cryptography lists.

I now compared those four names with the eight who had hyphenated “proof-of-work.” Only one overlapped: Back.

Even fewer people had used the phrase “partial pre-image” before Satoshi employed it on the Cryptography list to explain how bitcoin’s Hashcash-like mining function worked. The only two people I could find were Finney and Back, also in relation to Hashcash, with one crucial difference: Finney wrote “preimage” in one word whereas Back tended to hyphenate it — just like Satoshi.

The third linguistic marker I zeroed in on was the phrase “burning the money,” which Satoshi employed while discussing an escrow feature. He used it to mean destroying bitcoins. Before Satoshi, only one person had discussed “burning” an electronic coin on the Cypherpunks or Cryptography lists: Back, in April 1999.

From 34,000 Down to One

I wanted to find a more systematic way to analyze Satoshi’s writing, so I enlisted the help of Dylan Freedman, a journalist on The New York Times’ artificial-intelligence team who had experience with computational text analysis.

My strong belief was that Satoshi was a member of the cryptographic community that congregated on the Cypherpunks, Cryptography and Hashcash mailing lists because he knew several Cypherpunks, presented his white paper on the Cryptography list and incorporated Hashcash into bitcoin. We decided to collect archives of all three lists from the internet and merge them into one huge database to make them searchable.

Between 1992 and Oct. 30, 2008 — the day before Satoshi’s appearance — more than 34,000 users had posted to the three lists. Since many were spammers or users who posted just a few times, we eliminated anyone with fewer than 10 posts. That reduced our candidate pool to 1,615.

We also excluded users who had never discussed digital money. That left us with a smaller pool of 620 candidates. Together, those 620 people had written a total of 134,308 posts.

In a perfect world, we would analyze this trove without any risk of bias infecting the results. The field of stylometry prided itself on this, as Cafiero often reminded me. But stylometry had failed.

An alternate method was to identify all the words in the Satoshi corpus that didn’t have synonyms, and measure which of our 620 suspects used the most of those words. Words without synonyms tended to be technical terms, so this would weed out common ones. And it would have the added benefit of foiling any multiple-choice sentence constructor like the one Back had suggested, since words without synonyms couldn’t be substituted easily.

We gave this method a try. Back came out at the top of the list, with 521 synonym-less words shared with Satoshi. A few other Cypherpunks were not far behind, but they had all written many more posts than Back, which made him stand out even more.

Looking for more definitive evidence, we devised two additional approaches grounded in my reporting.

First, we drilled down on Satoshi’s grammatical hyphenation errors.

For the sake of our analysis, we made The New York Times stylebook the arbiter of correct hyphenation and fed its hyphens section into an artificial-intelligence model. Then we instructed the model to scan the Satoshi corpus: With its help, we identified 325 distinct errors in Satoshi’s use of hyphens.

When we compared those errors with the writings of our hundreds of suspects, Back was a clear outlier. He shared 67 of Satoshi’s exact hyphenation errors. The person with the second-most matches had 38.

Returning to our 620 suspects, I wanted to know how many of them shared the other writing tics I’d identified in Satoshi’s prose.

First, we screened for the posters who sometimes put two spaces between sentences like Satoshi did. That eliminated 58 people and left us with 562 suspects.

IV. Confrontation

El Salvador

I still did not have definitive proof of Satoshi’s identity. Only Satoshi himself could provide that, if he used a private key associated with one of bitcoin’s first blocks. But I now had a wealth of evidence.

In mid-November, I wrote to Back to request another interview. This time, I didn’t beat around the bush. I wrote that I had concluded that he was Satoshi and I wanted to show him everything I had uncovered and give him a chance to address it. I even offered to fly to Malta. Once again, he didn’t reply.

So I decided to approach him in person at a bitcoin conference where he was scheduled to speak in El Salvador two months later.

I landed in balmy San Salvador in late January with a plan. Back’s panel was on the conference’s second day. I would approach him then. But late on the afternoon of the first day, I noticed that he had posted photos of himself onstage at the conference on his X feed. Confused and worried I had missed my opportunity, I rushed to the speakers lounge, thinking I might find him there. But security guards denied me access, so I planted myself near the lounge entrance and kept my gaze fixed on the door.

Thirty minutes later, Back came out. I walked up to him, reintroduced myself and explained why I had come. He was slightly flustered but, to my pleasant surprise, he agreed to meet with me the next morning in the lobby of his hotel, which was doubling as the conference venue.

When I arrived at the appointed hour, Back was flanked by two executives from a new bitcoin treasury company he had co-founded. He explained that the company was in the process of going public, forcing him to be more careful about how he interacted with the press.

I had completely missed this new development. Bitcoin treasury companies borrow money and use it to amass bitcoins, providing investors with a more aggressive way to bet on the cryptocurrency. Back had started his last summer and was merging it with a publicly traded shell created by Cantor Fitzgerald, the Wall Street firm formerly led by Commerce Secretary Howard Lutnick. As chief executive of the merged company, Back was required under U.S. securities law to disclose any information that was material to its investors. A secret stash of 1.1 million coins that could crash the bitcoin market if it were suddenly sold, for example, would probably be considered material.

As I absorbed this new wrinkle, the four of us headed up to Back’s hotel room. Back looked tan and relaxed in a black T-shirt and black slacks.

Over the next two hours, I presented my evidence piece by piece. In his soft British lilt, Back insisted he wasn’t Satoshi and chalked it all up to a series of coincidences. But at times, his body language told a different story. His face reddened and he shifted uncomfortably in his seat when confronted with things that were harder to explain away.

For instance, Back didn’t have a good answer for why he disappeared from the Cryptography list during the period Satoshi was active, other than to say he was busy with work. Nor did he have a good answer for why he claimed on the “Let’s Talk Bitcoin” podcast that he had participated in the late 2008 list discussion sparked by Satoshi’s white paper, when he clearly hadn’t. When I pushed Back on both points, he turned defensive.

“Ultimately, it doesn’t prove anything. And I will reassure you, it’s really not me,” he said in a sharp tone.

When I brought up the results of our writing analyses, Back fumbled for an explanation but couldn’t find one.

“I don’t know,” he said. “It’s not me, but I take what you’re saying that this is what the AI said with the data. But it’s still not me.”

Back argued that it was hard to prove a negative. But he offered up one proof that he wasn’t Satoshi: the fact that he was so ignorant about bitcoin when he first joined the #bitcoin-wizards IRC channel that he mistakenly thought a bitcoin address functioned like a fluctuating bank balance. (A bitcoin address is more like a physical wallet containing dollar bills; the change you get back from a transaction is made up of entirely new digital coins.)

The rub was that there was no trace of this misunderstanding in the channel’s logs. When I pointed this out to Back, he made light of it: “It would be hilarious if I hallucinated it.” (In a subsequent email, he said it might have happened in another IRC channel that wasn’t logged.)

Back denied being Satoshi more than a half-dozen times, but I found the phrasing of one of those denials — after I pointed out that he had outlined virtually every aspect of bitcoin years before it was invented — revealing: “Clearly I’m not Satoshi, that’s my position.”

That sounded more like a rhetorical stance than a statement grounded in fact. But Back quickly caught himself and added: “And it’s true as well, for what it’s worth.”

Back did agree with me about some things. He acknowledged that he had the right background and skill set to be Satoshi. And he agreed that Satoshi was British, older than 50 and likely a member of the Cypherpunks. He also agreed with me about the inconsistency I’d noticed in the emails Satoshi had sent him: Satoshi would had to have known about b-money if he had read. Back’s Hashcash paper, Back conceded.

But he denied that the emails were a ruse to divert suspicion from himself. This might have been more convincing if he had agreed to produce the emails’ metadata. However, he continued to ignore my request for it.

I still had a few things I wanted to confront Back with, but his aides said he had other meetings to attend. We took the elevator back down to the lobby and shook hands like two chess players after a hard-fought match.

As I watched Back disappear into the crowd of jovial conferencegoers, something nagged at me. For a fleeting moment, I thought I had heard him slip and say something as though he was Satoshi himself. But I couldn’t remember what it was.

When I got home to New York, I found it in the recording I’d made of the interview. It was when I was walking him through the similarities between things he and Satoshi had written. I brought up one of Satoshi’s quotes, but before I had a chance to explain why I was mentioning it, Back interrupted.

Me: There’s a quote that I mentioned earlier where Satoshi says, “I’m better with code than with words.”

Back: I did a lot of talking though for somebody, I mean … I mean, I’m not saying I’m good with words but I sure did a lot of yakking on these lists actually.

To my ears, it sounded like he was saying that for someone who preferred code over words, he sure had written a lot of words. Implicit in that was an acknowledgment that he had been the one who wrote the quote. In other words, for a few seconds, Back had let the mask fall and turned into Satoshi.

I emailed him to confront him about it a few days later. He denied that it was a slip. “I was just responding conversationally to a general observation about technical people often feeling more comfortable expressing ideas in code than in prose,” he wrote.

But I had been crystal clear: I had asked about a specific Satoshi quote, and I suspected Back knew that.

I recalled how 10 years before, Satoshi had come out of hiding to help Back win the war over block size. And here Satoshi was, back again in a luxury hotel in El Salvador. Only this time, he had served Back less well because he’d removed any lingering doubt in my mind that I had the right man.