In 1987 James H. Ellis wrote a short, classified history of how the RSA cipher was secretly invented inside GCHQ three years before it was re-invented at MIT by Rivest, Shamir, and Adleman.

In his note, Ellis described how he first came to suspect that asymmetric cryptography might be possible, and how, after he had failed repeatedly to develop an asymmetric cipher, he came up with a formal proof, in 1970, that such a cipher definitely was possible. This resulted in a feverish and highly classified effort within GCHQ to invent one, a hunt which ended some years later when Clifford Cocks discovered what we now know as the RSA cipher. RSA was re-discovered some three years after that at MIT by its three eponymous (re-)inventors, changing cryptography for ever.

Ellis’ note was declassified by GCHQ in 1994 and posted online.

When read today in 2014, the proof makes no sense at all.

I’m...

How Bitcoin Works: A Guide for the Digitally Perplexed¹

This article was highlighted in the Boston Globe in 2014.

Suddenly in 2013, the word was everywhere: sometimes as “Bitcoin”, sometimes belittled as merely “bitcoin”. Bitcoin was used to buy a $130,000 luxury car, praised in solemn US Congressional committee hearings, but banned in China even as ATMs for it spread around the world. Its price on unregulated exchanges soared and plummeted wildly, from almost nothing to over $1,000 a coin.

The number of businesses and institutions that accepted Bitcoin surged, but nobody seemed to know whether the new currency was headed for an ignominious crash and oblivion, or whether instead it would be remembered as one of the defining inventions of the twenty-first century.

Here is how it works.