Adam Back: the inventor of Hashcash is cited in the bitcoin white paper and runs Blockstream

Adam Back is the British cryptographer who in 1997 invented Hashcash, the computational method on which bitcoin mining still rests today. Satoshi Nakamoto cites him by name in the 2008 bitcoin white paper. Since 2014 Back has been building infrastructure for bitcoin with the company Blockstream: the Liquid sidechain, a satellite service and the Jade hardware wallet. In April 2026 he also moved to the center of the question of who Satoshi is. He denies it.

For investors, Back is more than a footnote in crypto history. Anyone buying bitcoin today relies on a security model whose core he described almost three decades ago. How to buy bitcoin and what providers charge is shown in our buy bitcoin comparison. This profile sets out what Back invented, what Blockstream does and what there is to the Satoshi theory.

Who is Adam Back? Cryptographer, cypherpunk and Blockstream chief

Adam Back comes from Britain and belongs to the generation of the cypherpunks. That was the name of a loose group of programmers and cryptographers in the 1990s who saw strong encryption as a tool for privacy and digital freedom and debated on a shared mailing list. Many of the ideas that later came together in bitcoin originated in this circle: digital signatures, anonymous electronic cash and, indeed, computational work as proof.

Blockstream lists Back on its company website as co-founder and CEO and describes him as the inventor of Hashcash, the proof-of-work algorithm that bitcoin uses. The company names Adam Back, Erik Svenson, Pieter Wuille and others as its founders, with 2014 as the year it was established.

Hashcash in 1997: proof of work as a tool against spam

Hashcash is a method in which a sender has to perform a measurable amount of computational work before their message is accepted. According to the Hashcash project site, Adam Back invented Hashcash in 1997. The idea: a computer keeps searching for a number until the hash of a message begins with a certain number of zeros. That takes a moment. Verification by the recipient, by contrast, takes only a fraction of that time, because they recompute the hash once.

A hash function is a mathematical function that turns any data into a fixed-length checksum that cannot be reversed. According to the project site, Hashcash works with hash functions such as SHA-1 or SHA-256. For a single sender the effort is tiny. But anyone wanting to send millions of spam emails would have to solve millions of these puzzles. Computational work thus becomes a small postage stamp that spammers cannot afford.

Hashcash never caught on widely as a spam filter. The project site itself notes, however, where the method is used most today: as bitcoin's mining function.

The bitcoin white paper: Satoshi cites Adam Back at a key point

In the bitcoin white paper of October 2008, Satoshi Nakamoto describes how the network agrees on the order of transactions without a central authority. The decisive sentence in the section on proof of work reads: "To implement a distributed timestamp server on a peer-to-peer basis, we will need to use a proof-of-work system similar to Adam Back's Hashcash". In the list of references, Back's 2002 paper is source number six.

This passage is the reason Back appears in almost every history of bitcoin. Satoshi adopted the principle but changed its purpose: in bitcoin, the computational work protects not inboxes but the shared ledger. Anyone wanting to alter a confirmed transaction after the fact would have to redo all the computational work since that block and be faster than all honest miners combined.

Besides Back, the white paper names other forerunners, including Wei Dai with his b-money concept. The role the early pioneers played is also covered in our overview of the Satoshi suspects.

From the Hashcash stamp to bitcoin mining: what proof of work does today

Proof of work means exactly that: a participant proves, by solving a computational puzzle, that they have committed resources. In bitcoin these participants are called miners. Miners bundle new transactions into a block and search for a number that brings the block's double SHA-256 hash below a target value. Whoever finds it first may append the block and receives the block reward plus fees.

The difference from Hashcash lies in the difficulty. For a spam stamp, a puzzle that a laptop solves in seconds is enough. In bitcoin, the network adjusts the difficulty every 2,016 blocks so that a block is produced every ten minutes on average, no matter how much computing power is connected worldwide. This has given rise to an industry of its own, with specialized machines and large data centers.

For you as an investor, this means the security of your bitcoin is determined by the computing power of the entire network, not by any single company. This computational work also ensures that new bitcoin are created only on a fixed schedule. How many there are and how many are considered lost we calculated in our explainer How many bitcoin are there?.

Blockstream since 2014: sidechains, satellite and a hardware wallet

With Blockstream, Back founded a company that develops software and infrastructure around bitcoin. According to the company website, it offers several products that bitcoin users should know:

• Blockstream Satellite (since August 2017): The service broadcasts the bitcoin blockchain via satellite, so that a node can receive new blocks even without internet access. The second version has been running since May 2020.
• Liquid Network (since October 2018): A sidechain is a separate blockchain connected to bitcoin. You swap real bitcoin for so-called L-BTC and can move them there faster and more confidentially. The Tether stablecoin was added to Liquid in July 2019.
• Blockstream App (since March 2019): A software wallet for bitcoin and Liquid on smartphones.
• Jade (since January 2021): A hardware wallet that Blockstream describes as fully open source. Its successor, Jade Plus, came out in January 2025.

Liquid works differently from bitcoin itself. The real bitcoin backing L-BTC are held by a federation: a group of selected companies that jointly decide over the reserves by multisignature. That makes Liquid faster but requires trust in this group. How sensitive that point is became clear in the autumn of 2026.

Liquid Network: the September 6 attack and the return to full backing

On September 6, 2026, around 4,000 bitcoin, then worth about $320 million, flowed out of Liquid's federation wallet. We reported on it on September 7 in our article on the Liquid Network hack. According to Cointelegraph, the reserve had previously held around 4,200 bitcoin. The attackers described themselves as white hats and sent back 3,400 bitcoin on September 7, after Blockstream had secured the affected bridge nodes. They kept around 598 bitcoin.

Blockstream said on September 11 that it would not pay a ransom for the remaining coins, according to The Block. On November 3 the Liquid federation reported that the reserves were fully backed again, one to one for all L-BTC. The federation did not say where the missing roughly 600 bitcoin came from. Samson Mow, a member of the federation's board, named Blockstream as the source, according to The Block and Decrypt, paid in three tranches of 50, 300 and 250 bitcoin.

For sidechain users there is a lesson. Anyone who swaps bitcoin for L-BTC takes on an additional risk: that of the federation, its software and its bridge back to bitcoin. This time no damage was done because the attackers and the operators reached an agreement and Blockstream made up the rest. That is no guarantee for future cases.

The Satoshi theory: The New York Times versus Adam Back's denial

On April 8, 2026, The New York Times published an investigation by two-time Pulitzer Prize winner John Carreyrou. According to Decrypt, Carreyrou concluded after 18 months that Adam Back is Satoshi Nakamoto. He had compared up to 620 suspects on the basis of their writing from years of forum posts and emails. Quirks in spelling, errors and technical vocabulary reportedly pointed to Back. In addition there were conversations with Back himself, including in El Salvador.

Back contradicted it on X the same day. According to Decrypt, he wrote that he is not Satoshi and called the investigation a combination of coincidence and similar phrasing by people with similar experience and similar interests. He spoke of a degree of confirmation bias on the author's part. As early as 2020, Back had denied creating bitcoin in an interview with Bloomberg.

Only one thing is solid to this day: no one has presented cryptographic proof. Such proof would be, for example, a signature with a key from the first bitcoin blocks attributed to Satoshi. Style comparisons can provide clues but do not replace that proof. The question therefore remains open, and Back himself answers it in the negative.

What investors can take from Back's work: mining security, Liquid and self-custody

Back's work yields three practical points for bitcoin investors. First, proof of work secures the network: the more computing power is connected, the more expensive an attack on the blockchain becomes. That is one of the reasons bitcoin is considered particularly robust, and it is an argument that holds regardless of the price.

Second, Liquid shows that additional layers bring convenience and add risks. Anyone holding L-BTC should know that a federation stands behind it. For long-term investment, bitcoin on your own address is the simpler solution.

Third, Blockstream stands for the idea of self-custody: you hold your private keys yourself instead of leaving your coins with an exchange. A hardware wallet stores the key on a separate device that is not connected to the internet. Jade is one of several options. Which devices exist and how they differ is shown in our hardware wallet comparison.

Adam Back: the Hashcash of 1997 is in every bitcoin block

Satoshi or not, Back's contribution to bitcoin is written in the white paper and in every block that is found. If you want to draw something from it for your own investment, there are three steps:

1. Buy bitcoin from a vetted provider: fees, spreads and the licensing of providers are set out in our buy bitcoin comparison.
2. Invest regularly instead of all at once: a savings plan spreads your entry over many prices. Which providers offer one and from what amount is shown in the bitcoin savings plan comparison.
3. Hold your coins yourself: larger holdings belong on a hardware wallet whose keys only you know. You can find an overview of the devices in the hardware wallet comparison.

(As of November 14, 2026. This article is not investment advice. Prices and fee structures change; check the terms with the provider before you buy.)