time, for ordinary people to encrypt, or scramble, messages in a way that could be decrypted only by the intended recipient and not cracked even by the most powerful supercomputers.
Every user of the new technology, known as public-key cryptography, would receive a public keyâa unique jumble of letters and numbers that serves as a sort of address that could be distributed freelyâand a corresponding private key, which is supposed to be known only by the user. The two keys are related, mathematically, in a way that ensures that only the userâletâs call her Alice, as cryptographers often didâwith her private key, can unlock messages sent to her public key, and only she can sign off on messages associated with her public key. The unique relationship between each public and private key was determined by complicated math equations that were constructed so cleverly that no one with a particular public key would ever be able to work backward to figureout the corresponding private keyânot even the most powerful supercomputer. This whole setup would later play a central role in the Bitcoin software.
Hal was introduced to the potential of public-key cryptography in 1991 by the pathbreaking cryptographer David Chaum, who had been experimenting with ways to use public-key cryptography to protect individual privacy.
âIt seemed so obvious to me,â Hal told the other Cypherpunks of his first encounter with Chaumâs writing. âHere we are faced with the problems of loss of privacy, creeping computerization, massive databases, more centralizationâand Chaum offers a completely different direction to go in, one which puts power into the hands of individuals rather than governments and corporations.â
As usual, when Hal found something exciting, he didnât just passively read up on it. On nights and weekends, after his job as a software developer, he began helping with a volunteer project, referred to as Pretty Good Privacy, or PGP, which allowed people to send each other messages that could be encrypted using public-key cryptography. The founder of the project, Phil Zimmerman, was an antinuclear activist who wanted to give dissidents a way to communicate outside the purview of governments. Before long, Zimmerman brought Hal on as the first employee at PGP.
Idealistic projects like PGP generally had a small audience. But the potential import of the technology became apparent when federal prosecutors launched a criminal investigation into PGP and Zimmerman. The government categorized encryption technology, such as PGP, as weapon-grade munitions, and this designation made it illegal to export. While the case was eventually dropped, Hal had to lie low with his own involvement in PGP for years and could never take credit for some of his important contributions to the project.
T HE E XTROPIANS AND Cypherpunks were working on several different experiments that could help empower individuals against traditional sources of authority. But money was, from the beginning, at the center of their efforts to reimagine the future.
Money is to any market economy what water, fire, or blood is to the human ecosystemâa basic substance needed for everything else to work. For programmers, existing currencies, which were valid only within particular national borders and subject to technologically incompetent banks, seemed unnecessarily constrained. The science fiction that Hal and others had grown up on almost always featured some kind of universal money that could span galaxiesâin Star Wars it was the galactic credit standard; in the Nightâs Dawn trilogy it was Jovian credit.
Beyond these more fanciful ambitions, the existing financial system was viewed by the Cypherpunks as one of the biggest threats to individual privacy. Few types of information reveal as much about a person like Alice, the cryptographersâ favorite, as her financial transactions. If snoopers get access to her